hypothesis of why we dream

Why Do We Dream? A New Theory on How It Protects Our Brains

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W hen he was two years old, Ben stopped seeing out of his left eye. His mother took him to the doctor and soon discovered he had retinal cancer in both eyes. After chemotherapy and radiation failed, surgeons removed both his eyes. For Ben, vision was gone forever.

But by the time he was seven years old, he had devised a technique for decoding the world around him: he clicked with his mouth and listened for the returning echoes. This method enabled Ben to determine the locations of open doorways, people, parked cars, garbage cans, and so on. He was echolocating: bouncing his sound waves off objects in the environment and catching the reflections to build a mental model of his surroundings.

Echolocation may sound like an improbable feat for a human, but thousands of blind people have perfected this skill, just like Ben did. The phenomenon has been written about since at least the 1940s, when the word “echolocation” was first coined in a Science article titled “Echolocation by Blind Men, Bats, and Radar.”

How could blindness give rise to the stunning ability to understand the surroundings with one’s ears? The answer lies in a gift bestowed on the brain by evolution: tremendous adaptability.

Whenever we learn something new, pick up a new skill, or modify our habits, the physical structure of our brain changes. Neurons, the cells responsible for rapidly processing information in the brain, are interconnected by the thousands—but like friendships in a community, the connections between them constantly change: strengthening, weakening, and finding new partners. The field of neuroscience calls this phenomenon “brain plasticity,” referring to the ability of the brain, like plastic, to assume new shapes and hold them. More recent discoveries in neuroscience suggest that the brain’s brand of flexibility is far more nuanced than holding onto a shape, though. To capture this, we refer to the brain’s plasticity as “livewiring” to spotlight how this vast system of 86 billion neurons and 0.2 quadrillion connections rewires itself every moment of your life.

Neuroscience used to think that different parts of the brain were predetermined to perform specific functions. But more recent discoveries have upended the old paradigm. One part of the brain may initially be assigned a specific task; for instance, the back of our brain is called the “visual cortex” because it usually handles sight. But that territory can be reassigned to a different task. There is nothing special about neurons in the visual cortex: they are simply neurons that happen to be involved in processing shapes or colors in people who have functioning eyes. But in the sightless, these same neurons can rewire themselves to process other types of information.

Mother Nature imbued our brains with flexibility to adapt to circumstances. Just as sharp teeth and fast legs are useful for survival, so is the brain’s ability to reconfigure. The brain’s livewiring allows for learning, memory, and the ability to develop new skills.

In Ben’s case, his brain’s flexible wiring repurposed his visual cortex for processing sound. As a result, Ben had more neurons available to deal with auditory information, and this increased processing power allowed Ben to interpret soundwaves in shocking detail. Ben’s super-hearing demonstrates a more general rule: the more brain territory a particular sense has, the better it performs.

Recent decades have yielded several revelations about livewiring, but perhaps the biggest surprise is its rapidity. Brain circuits reorganize not only in the newly blind, but also in the sighted who have temporary blindness. In one study, sighted participants intensively learned how to read Braille. Half the participants were blindfolded throughout the experience. At the end of the five days, the participants who wore blindfolds could distinguish subtle differences between Braille characters much better than the participants who didn’t wear blindfolds. Even more remarkably, the blindfolded participants showed activation in visual brain regions in response to touch and sound. When activity in the visual cortex was temporarily disrupted, the Braille-reading advantage of the blindfolded participants went away. In other words, the blindfolded participants performed better on the touch-related task because their visual cortex had been recruited to help. After the blindfold was removed, the visual cortex returned to normal within a day, no longer responding to touch and sound.

But such changes don’t have to take five days; that just happened to be when the measurement took place. When blindfolded participants are continuously measured, touch-related activity shows up in the visual cortex in about an hour.

What does brain flexibility and rapid cortical takeover have to do with dreaming? Perhaps more than previously thought. Ben clearly benefited from the redistribution of his visual cortex to other senses because he had permanently lost his eyes, but what about the participants in the blindfold experiments? If our loss of a sense is only temporary, then the rapid conquest of brain territory may not be so helpful.

And this, we propose, is why we dream.

In the ceaseless competition for brain territory, the visual system has a unique problem: due to the planet’s rotation, all animals are cast into darkness for an average of 12 out of every 24 hours. (Of course, this refers to the vast majority of evolutionary time, not to our present electrified world.) Our ancestors effectively were unwitting participants in the blindfold experiment, every night of their entire lives.

So how did the visual cortex of our ancestors’ brains defend its territory, in the absence of input from the eyes?

We suggest that the brain preserves the territory of the visual cortex by keeping it active at night. In our “defensive activation theory,” dream sleep exists to keep neurons in the visual cortex active, thereby combating a takeover by the neighboring senses. In this view, dreams are primarily visual precisely because this is the only sense that is disadvantaged by darkness. Thus, only the visual cortex is vulnerable in a way that warrants internally-generated activity to preserve its territory.

In humans, sleep is punctuated by rapid eye movement (REM) sleep every 90 minutes. This is when most dreaming occurs . (Although some forms of dreaming can occur during non-REM sleep, such dreams are abstract and lack the visual vividness of REM dreams.)

REM sleep is triggered by a specialized set of neurons that pump activity straight into the brain’s visual cortex, causing us to experience vision even though our eyes are closed. This activity in the visual cortex is presumably why dreams are pictorial and filmic. (The dream-stoking circuitry also paralyzes your muscles during REM sleep so that your brain can simulate a visual experience without moving the body at the same time.) The anatomical precision of these circuits suggests that dream sleep is biologically important—such precise and universal circuitry rarely evolves without an important function behind it.

The defensive activation theory makes some clear predictions about dreaming. For example, because brain flexibility diminishes with age, the fraction of sleep spent in REM should also decrease across the lifespan. And that’s exactly what happens: in humans, REM accounts for half of an infant’s sleep time, but the percentage decreases steadily to about 18% in the elderly. REM sleep appears to become less necessary as the brain becomes less flexible.

Of course, this relationship is not sufficient to prove the defensive activation theory. To test it on a deeper level, we broadened our investigation to animals other than humans. The defensive activation theory makes a specific prediction: the more flexible an animal’s brain, the more REM sleep it should have to defend its visual system during sleep. To this end, we examined the extent to which the brains of 25 species of primates are “pre-programmed” versus flexible at birth. How might we measure this? We looked at the time it takes animals of each species to develop. How long do they take to wean from their mothers? How quickly do they learn to walk? How many years until they reach adolescence? The more rapid an animal’s development, the more pre-programmed (that is, less flexible) the brain.

As predicted, we found that species with more flexible brains spend more time in REM sleep each night. Although these two measures—brain flexibility and REM sleep—would seem at first to be unrelated, they are in fact linked.

As a side note, two of the primate species we looked at were nocturnal. But this does not change the hypothesis: whenever an animal sleeps, whether at night or during the day, the visual cortex is at risk of takeover by the other senses. Nocturnal primates, equipped with strong night vision, employ their vision throughout the night as they seek food and avoid predation. When they subsequently sleep during the day, their closed eyes allow no visual input, and thus, their visual cortex requires defense.

Dream circuitry is so fundamentally important that it is found even in people who are born blind. However, those who are born blind (or who become blind early in life) don’t experience visual imagery in their dreams; instead, they have other sensory experiences, such as feeling their way around a rearranged living room or hearing strange dogs barking. This is because other senses have taken over their visual cortex. In other words, blind and sighted people alike experience activity in the same region of their brain during dreams; they differ only in the senses that are processed there. Interestingly, people who become blind after the age of seven have more visual content in their dreams than those who become blind at younger ages. This, too, is consistent with the defensive activation theory: brains become less flexible as we age, so if one loses sight at an older age, the non-visual senses cannot fully conquer the visual cortex.

If dreams are visual hallucinations triggered by a lack of visual input, we might expect to find similar visual hallucinations in people who are slowly deprived of visual input while awake. In fact, this is precisely what happens in people with eye degeneration, patients confined to a tank-respirator, and prisoners in solitary confinement. In all of these cases, people see things that are not there.

We developed our defensive activation theory to explain visual hallucinations during extended periods of darkness, but it may represent a more general principle: the brain has evolved specific circuitry to generate activity that compensates for periods of deprivation. This might occur in several scenarios: when deprivation is regular and predictable (e.g., dreams during sleep), when there is damage to the sensory input pathway (e.g., tinnitus or phantom limb syndrome), and when deprivation is unpredictable (e.g., hallucinations induced by sensory deprivation). In this sense, hallucinations during deprivation may in fact be a feature of the system rather than a bug.

We’re now pursuing a systematic comparison between a variety of species across the animal kingdom. So far, the evidence has been encouraging. Some mammals are born immature, unable to regulate their own temperature, acquire food, or defend themselves (think kittens, puppies, and ferrets). Others are born mature, emerging from the womb with teeth, fur, open eyes, and the abilities to regulate their temperature, walk within an hour of birth, and eat solid food (think guinea pigs, sheep, and giraffes). The immature animals have up to 8 times more REM sleep than those born mature. Why? Because when a newborn brain is highly flexible, the system requires more effort to defend the visual system during sleep.

Since the dawn of communication, dreams have perplexed philosophers, priests, and poets. What do dreams mean ? Do they portend the future? In recent decades, dreams have come under the gaze of neuroscientists as one of the field’s central unsolved mysteries. Do they serve a more practical, functional purpose? We suggest that dream sleep exists, at least in part, to prevent the other senses from taking over the brain’s visual cortex when it goes unused. Dreams are the counterbalance against too much flexibility. Thus, although dreams have long been the subject of song and story, they may be better understood as the strange lovechild of brain plasticity and the rotation of the planet.

For more information:

Eagleman DM (2020). Livewired: The Inside Story of the Ever-Changing Brain. New York: Pantheon.
Eagleman DM, Vaughn DA (2020). The defensive activation theory: dreaming as a mechanism to prevent takeover of the visual cortex .

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A New Theory for Why We Dream

Tufts researcher Erik Hoel draws on machine learning and evolutionary science in his hypothesis about our nightly visits to dreamland

What’s the point of dreams? We all have them, for hours each day of our lives, even if we don’t remember. Plenty of mammals and birds dream, too. When you see Fido sound asleep with his eyes rapidly moving, his paws twitching, you know for sure that he’s in dreamland.

Lots of theories have been offered: dreams are used to regulate emotion, like dealing with fears; to consolidate memory, replaying things from your day to help remember them; to solve, or on the other hand to forget, real-world problems. Another theory suggests they help the brain predict its own future states.

None of those theories seem quite right to Erik Hoel, a research assistant professor at Tufts’ Allen Discovery Center who studies consciousness, modeling the relationships between experiences and brain states.

In his research, Hoel works with artificial neural networks—machine learning. Think of Deep Mind, the Google artificial intelligence program that beat the best human players at the almost infinitely complex Japanese strategy game Go.

It turns out that when such machine learning programs do the same task again and again, they can become “overfit”—able to do that one thing really well, but not to learn lessons and create general knowledge that can be applied to different tasks. To prevent that, programmers often introduce random variables, or noise in the data.

In essence, that’s what Hoel thinks our brains are doing when we dream: breaking the cycle of repetitive daily tasks—filling out spreadsheets, delivering mail, tightening pipe fittings—with an infusion of discord, keeping our brains fit.

Have you ever had a problem that just seemed to defy solution? You think and think, but you remain stuck. Then you go to bed, wake up the next morning, and presto, the solution appears. It might well be, Hoel would say, that your thinking was overfitted for the task—just like a machine learning program in need of disruption.

“This fits with anecdotal reports of plateauing in terms of performance on a task, like a video game, only to sleep and have increased performance the next day,” Hoel says. “There is also the long-standing traditional association between dreams and creativity.”

He recently published a paper on what he calls the overfitted brain hypothesis, and it’s been garnering attention in the press—it was the cover story for a recent issue of New Scientist magazine.

The Evolution of a Purpose

How Hoel came to the theory surprisingly begins not with neuroscience, but fiction.

When he was young, he loved reading. His mother ran the bookstore Jabberwocky in Newburyport, Mass., and he spent a lot of time there, like the proverbial kid in a candy store, immersed in fictional worlds. He always wanted to be a writer, but ended up studying cognitive science at Hampshire College, and went on to get a Ph.D. in neuroscience. (He did become a fiction writer, too: his novel The Revelations will be published by the Overlook Press in early April.)

“I don’t think dogs are imbuing their dreams with meaning, but they still dream,” he says. “Humans can imbue their dreams with meaning, but dreams should still have a purpose for all mammals who regularly do it,” says Erik Hoel.

His focus as a student was consciousness, but his love of reading also made him wonder why people are so drawn to reading novels, “which always struck me from a scientific perspective as kind of a very strange activity,” he says. “Fictions are essentially lies—there’s no such thing as Hogwarts. Harry Potter never went there. It’s the opposite of facts.”

Fiction has all sorts of purposes—aesthetic, emotional, even political—but probably also has an evolutionary role, Hoel says. “I think that one could argue that there is a sort of deep biological need for fictions in humans,” he says. Just look at all the TV shows, novels, movies, and video games we consume for an ungodly amount of our waking hours. Those diversions “actually serve deep down some sort of fundamental purpose,” he says.

He soon started seeing links between fiction and dreaming. Take the short stories by Jorge Borges, Hoel says. They are rife with narrative and yet quite otherworldly at the same time—just like dreams. It made him think there must be some evolved purpose of dreaming, a function seen across many species of animals.

He soon started to research sleep and dreaming. But looking closely at the scientific literature about dreaming, he came away with more questions than answers. One prominent recent theory says dreams are created for memory consolidation; but why, Hoel asks, do the dreams so rarely actually mimic those memories? Another says that dreams are for emotion processing, but there’s little empirical evidence for it.

One fact that many dream theories also overlook is that while reptiles and many other animals don’t dream, mammals and birds apparently do. “Dreaming is so ubiquitous across mammals and even birds that there must be a good reason for it,” he says.

It’s widely noted in neuroscience that many traits are highly conserved, meaning that brains seem to operate in much the same way across the animal kingdom, Hoel says. The human brain, while “basically getting more bang for your buck in terms of space and having some more frontal and prefrontal regions, is not significantly different in its neuroanatomy from a canine’s,” he points out.

It’s also true, Erik Hoel says, that “evolution is a great multitasker, so I’d be surprised if there’s just one absolute reason for dreaming and no other reason.”

So what does differentiate mammals from reptiles? “Mothers,” says Hoel. “When an iguana is born, nature’s basically just booting up the iguana program—almost everything is just innate for them.” Reptiles therefore don’t actively learn. On the other hand, young mammals learn from their moms (and dads, too) as they develop and are cared for.

It’s unsurprising, Hoel says, that the creatures that have to learn to survive have the most pronounced dreaming and signs of dreaming. It’s likely a sign of dreaming’s evolutionary importance for learning—and survival.

The Human Secret

While metaphors of brains as computers is a bit overdone, Hoel says, in this case, reversing the metaphor to say that brains are like neural networks is close to the mark. After all, he says, those neural networks were designed by engineers to mimic human circuitry.

The overlap between how humans dream, and how machine learning experts avoid pure memorization and help programs transfer knowledge from one problem to others “lends credence to the idea that the evolved function of dreaming is for precisely these purposes,” he says. “It seems that the most effective way to trigger dreams about something is to have subjects perform repetitively on a novel task like Tetris, likely because the visual system has become overfitted to the task.”

Sleep is widely known to have a restorative effect—just try going without it for a day or two and see how well you function. Precisely how that works is not completely known. Current thinking is that sleep evolved as some sort of metabolic housekeeping activity—at one stage of sleep, the cerebral spinal fluid essentially flushes waste products through the lymphatic system.

But dreaming seems to happen during other parts of sleep, and apparently occurs more than we realize; we tend to remember our dreams only if we wake in their midst. Hoel’s theory is that dreaming is an exaptation, a trait that evolved for one purpose but later takes on others.

In this case, he says, “sleep evolved for molecular housekeeping purposes, and only when brains had to significantly learn during the organism’s lifetime did the goal of avoiding overfitting and increasing generalization become adaptive.”

Another key feature of Hoel’s theory is that it “takes the phenomenology of dreams seriously.” Our nightly hallucinogenic narratives, “containing fabulist and unusual events,” are exactly what dreams would be if they were fulfilling the role Hoel proposes—adding noise to the thinking system.

“The point of dreams is the dreams themselves, since they provide departures away from the statistically-biased input of an animal’s daily life, which can therefore increase performance,” he says. “It may seem paradoxical, but a dream of flying may actually help you keep your balance running.”

And what about dreams that seem to be speaking to us—helping us understand our lives, remember loved ones, or even scare us?

Meaning in dreams, he says, is basically a side effect. “I don’t think dogs are imbuing their dreams with meaning, but they still dream,” he says. “Humans can imbue their dreams with meaning, but dreams should still have a purpose for all mammals who regularly do it,” Hoel says.

It’s also true, he says, that “evolution is a great multitasker, so I’d be surprised if there’s just one absolute reason for dreaming and no other reason.”

Hoel comes back to where he started: fiction. “It is worth considering whether fictions, like novels or films, act as artificial dreams, accomplishing at least some of the same function,” he says.

His theory, he says, “suggests fictions, and perhaps the arts in general, may actually have an underlying cognitive utility in the form of improving generalization and preventing overfitting.”

The tradition of fiction goes back much further than the first novel, he says—maybe to the first storytelling shamans. “Maybe that’s part of the human secret—we export some of our learning finessing outside of the body, so that you don’t have to just do it through dreams,” he says. “You can do it through these artificial dreams that maybe even are more impactful because they’re so well structured.”

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What Is the Activation-Synthesis Model of Dreaming?

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Huma Sheikh, MD, is a board-certified neurologist, specializing in migraine and stroke, and affiliated with Mount Sinai of New York.

Origins of the Theory

The sleeping brain, key things to remember, reaction to the theory, are dreams meaningless, the aim model of dreaming.

The activation-synthesis theory is a neurobiological explanation of why we dream. The question of why people dream has perplexed philosophers and scientists for thousands of years, but it is only fairly recently in history that researchers have been able to take a closer look at exactly what happens in the body and brain during dreaming.

Harvard psychiatrists J. Allan Hobson and Robert McCarley first proposed their theory in 1977, suggesting that dreaming results from the brain's attempt to make sense of neural activity that takes place during sleep.

Even when you are sleeping, your brain is active. Hobson and McCarley suggested that during sleep, activity in some of the lower levels of the brain that are primarily responsible for basic biological processes are then interpreted by the parts of the brain responsible for higher-order functions such as thinking and processing information.

The activation-synthesis model suggests that dreams are caused by the physiological processes of the brain. While people used to believe that sleeping and dreaming was a passive process, researchers now know that the brain is anything but quiet during sleep.

So what sort of things are happening in the sleeping brain? A wide variety of neural activity takes place as we slumber.

Sleep helps the brain perform a number of activities including cleaning up the brain and consolidating memories from the previous day. Activation-synthesis theory suggests that the physiological processes that take place as we sleep are the cause of dreams.

Brain Activity Plays a Role in Dreaming

How does brain activity during sleep lead to dreaming?

According to Hobson and other researchers, circuits in the brain stem are activated during REM sleep.
Once these circuits are activated, areas of the limbic system involved in emotions , sensations, and memories, including the amygdala and hippocampus , become active.
The brain synthesizes and interprets this internal activity and attempts to create meaning from these signals, which results in dreaming.

Common Characteristics of Dreams

Hobson also suggested that there are five key characteristics of dreams. Dreams tend to contain illogical content, intense emotions, acceptance of strange content, strange sensory experiences, and difficulty remembering dream content.

To summarize, the activation-synthesis theory essentially made three key assumptions:

High levels of activity in the brainstem are necessary for dreaming to take place.
Activation in these areas of the brain results in REM sleep and dreaming, and by corollary, all dreaming takes place during REM sleep.
The forebrain attempts to place meaning on the random signals created from the activation of the brainstem, resulting in coherent dreams.

So why does the brain try to make meaning from these random signals that take place during sleep?

"The brain is so inexorably bent upon the quest for meaning that it attributes and even creates meaning when there is little or none in the data it is asked to process," Hobson suggested.

The initial publication of their research stirred up considerable controversy, particularly among Freudian analysts. Because many dream researchers and therapists invest considerable time and effort trying to understand the underlying meaning of dreams , the suggestion that dreams were simply the brain's way of making sense of activity during sleep did not sit well with many.

While the activation-synthesis model of dreaming relies on physiological processes to explain dreaming, it does not imply that dreams are meaningless.

According to Hobson, "Dreaming may be our most creative conscious state, one in which the chaotic, spontaneous recombination of cognitive elements produces novel configurations of information: new ideas. While many or even most of these ideas may be nonsensical, if even a few of its fanciful products are truly useful, our dream time will not have been wasted."

Thanks to modern advances in brain imaging and the ability to monitor brain activity, researchers now understand more about the sleep-wake cycle, the different stages of sleep, and the different states of consciousness .

The more recent version of the activation-synthesis theory is known as the AIM model, standing for activation, input-output gating, and modulation.

This newer model tries to capture what happens in the brain-mind space as consciousness changes through waking, non-REM, and REM sleep states.

A Word From Verywell

The reasons and meanings behind dreaming have fascinated philosophers and researchers for centuries. Activation-synthesis theory added an important dimension to our understanding of why we dream and stressed the importance of neural activity during sleep.

As new technology emerges for studying the brain and sleep processes, researchers will continue to make new advances in our understanding of why we dream, in knowledge regarding states of consciousness, and in comprehending the possible meaning behind our dreams.

Hobson JA, McCarley RW. The brain as a dream-state generator: An activation-synthesis hypothesis of the dream process. Am J Psychiatry. 1977;134(12):1335-1348. doi:10.1176/ajp.134.12.1335

Oniz A, Inanc G, Taslica S, Guducu C, Ozgoren M. Sleep Is a Refreshing Process: An fNIRS Study. Front Hum Neurosci . 2019;13:160. doi:10.3389/fnhum.2019.00160

American Psychological Association. APA Dictionary of Psychology. AIM Model. Washington, DC: American Psychological Association 2020 https://dictionary.apa.org/aim-model

Hobson, JA. REM sleep and dreaming: Towards a theory of protoconsciousness. Nature Reviews Neuroscience . 2010;10(11): 803–813. doi:10.1038/nrn2716

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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Why Do We Dream? A New Theory on How It Protects Our Brains

For our new hypothesis about the function of dreams, see our paper: Eagleman DM, Vaughn DA (2020). The defensive activation theory: dreaming as a mechanism to prevent takeover of the visual cortex . Front Neurosci . 2021 May 21;15:632853. doi: 10.3389/fnins.2021.632853

For a summary of the ideas, see our article in Time Magazine: When he was two years old, Ben stopped seeing out of his left eye. His mother took him to the doctor and soon discovered he had retinal cancer in both eyes. After chemotherapy and radiation failed, surgeons removed both his eyes. For Ben, vision was gone forever.

"David Eagleman offers startling lessons.... His method is to ask us to cast off our lazy commonplace assumptions. - The Guardian

"David Eagleman is the kind of guy who really does make being a neuroscientist look like fun." - New York Times

"What Eagleman seems to be calling for is a new Enlightenment." - Sunday Herald

"A popularizer of impressive gusto...[Eagleman] aims, grandly, to do for the study of the mind what Copernicus did for the study of the stars." - New York Observer

"[A] neuroscientist and polymath." - Wall Street Journal

"Eagleman has a talent for testing the untestable, for taking seemingly sophomoric notions and using them to nail down the slippery stuff of consciousness." - The New Yorker

"David Eagleman may be the best combination of scientist and fiction-writer alive." - Stewart Brand

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The Brain Facts Book

The Science of Dreams

Published 29 Apr 2022
Author Charlotte Stoddart
Source Knowable Magazine

Freud thought that dreams were the gateway to our unconscious mind. Today, many scientists think the opposite: that the dreaming brain is quite similar to our awake, conscious state. But dreaming is a very personal experience and one that we can’t share — making the phenomenon very difficult to study. We still don’t know for sure why we dream, but in season 2, episode 1 of the Knowable Magazine podcast , we'll hear how psychologists, neuroscientists and philosophers have been trying to answer that question.

Hyperlinks to scientists and papers are included in the transcript.

About the Author

Charlotte Stoddart

Charlotte Stoddart is a freelance science filmmaker and podcaster. Charlotte was formerly the Chief Multimedia Editor at Nature.

CONTENT PROVIDED BY

Knowable Magazine

Knowable Magazine is an independent journalistic endeavor from Annual Reviews.

What did you dream about last night while you were sleeping?

When you woke up, did you remember your dream? Can you still remember it? How reliable is that memory?

Dreaming is one of the most impractical things a scientist could choose to study. Dreams are a universal part of human experience. But they are by nature subjective. We can’t share them. How can we understand dreams in general then, beyond the vague, untrustworthy recollections that we have of them when we’re awake? How can we study them scientifically and answer the question: Why do we dream?

This is Knowable . And I’m Charlotte Stoddart.

People have been trying to explain dreams for millennia. For a long time, these explanations were rooted in spiritual beings outside of our bodies; dreams were understood as messages from gods or as communications from our ancestors. The scientific study of dreams as something that happens in the brain began with Freud right at the dawn of the 20th century.

In his book “The Interpretation of Dreams,” Freud famously sets out his theory of dreams as the fulfilment of our unconscious wishes. He expands this theory in a later book called “Dream Psychology,” in which he describes the dreams of his patients and explains how to analyze them:

What is common in all these dreams is obvious. They completely satisfy wishes excited during the day which remain unrealized. They are simply and undisguisedly realizations of wishes.

With these books and his other work, Freud founded the field of psychoanalysis. His psychoanalytic approach is often seen as unscientific. But it’s likely that Freud actually wanted to study the dreaming brain in a scientific way; he just didn’t have the tools to do it. As a young researcher at the University of Vienna, Freud spent years studying the nervous system of sea lamprey and eels, publishing several scientific papers on his findings. Freud also studied human nerve cells, using a microscope to see his tissue samples. But a microscope was no use for studying the dreaming brain of live, sleeping human subjects.

Allan Hobson : “I think Freud understood that to really study dreaming, you had to know what was going on in the brain. He just couldn’t do it. I mean, there were no instruments; the technology wasn’t available to study the brain. So he dropped the brain side of the story and devoted himself solely to the psychological side. And of course, that was bold move, but it’s obviously inadequate.”

Psychedelics open a new window on the mechanisms of perception

That’s Allan Hobson , emeritus professor of psychiatry at Harvard Medical School. Hobson studied sleep and the dreaming brain for six decades, right up until his death at the age of 88 , a few weeks after he spoke to me. He was able to do what Freud couldn’t, thanks to an invention in Germany in the 1920s.

Hans Berger was a psychiatrist with a particular interest in psychic phenomena. He wanted to find correlations between brain activity and psychic events. And this led him to come up with a way to record electrical activity in the brain. He experimented with inserting silver electrodes under the scalp, and with placing the electrodes on the surface of his patients’ heads, as is done today. Berger’s recordings revealed patterns of electrical activity that looked like waves when transcribed on paper. He called them electroencephalograms, now known simply as EEGs .

Scientists and doctors began using EEGs to document differences in brain wave patterns between people and during different activities. The breakthrough for dreaming came in the 1950s, at the University of Chicago, where Eugene Aserinsky was trying to launch his career as a physiologist. At that time, sleep was thought of as a period when the brain switches off and rests. And in keeping with that, EEG recordings showed slow waves indicating low-level activity in the brain’s cortex. Not much going on, not much to study. But Aserinsky’s supervisor — Nathaniel Kleitman — thought differently and told Aserinsky to focus on researching sleep.

One evening, Aserinsky decided to hook his 8-year-old son up to an EEG machine , attaching electrodes to his skull and the skin around his eyes. While his son slept, Aserinsky watched the brain patterns produced by the machine. At first he saw the slow waves that he expected, a telltale sign of sleep. But at one point he noticed that the pens tracking his son’s eye movements — as well as the ones registering brain activity — were swinging back and forth, recording jerky eye movements and faster brain waves.

Aserinsky went to check on his son, expecting to find him wide awake and looking around. But the boy was still asleep. Aserinsky observed the same kind of brain activity in other sleeping subjects. It was characterized by rapid eye movements and became known as — you guessed it — rapid eye movement or REM sleep. Aserinsky realized that sleepers could have multiple periods of REM sleep during the night and, crucially, that when people were woken up during REM sleep they were more likely to recall vivid dreams.

By 1973, when a review on sleep was published in the Annual Review of Psychology , it was clear that there were at least two different stages of sleep: slow wave sleep that became known as non-REM sleep, and REM sleep, during which the brain is more active:

As data develop on the phenomenology of sleep states, it becomes increasingly clear that sleep is not simply a resting state, waxing and waning near the lower pole of a continuum of vigilance. Instead, sleep appears to be an extremely complex, constantly changing, but cyclic succession of psychophysiological patterns, qualita¬tively rather than quantitatively different from those of waking.

Keep this thought in mind, because at the end of this podcast we’ll return to the idea of sleep — and in particular dreaming — as not so different from our conscious awake state.

So, the invention of EEG showed that the sleeping brain is an active organ, not simply a resting one. Now there was a way to go beyond our unreliable recollections of dreams and actually study the phenomenon of dreaming. Now scientists could monitor the sleeping brain and they knew when during sleep a person was likely to be dreaming. This was a game changer, says sleep researcher Erin Wamsley :

Erin Wamsley : “It was the discovery of EEG that launched this kind of modern — second half of the 20th century — field of dreaming. And so the discovery of rapid eye movement sleep really is what kicked off the modern era, the post-Freud era of dream research. And so that was all about looking for what is the biological sign that someone is dreaming.”

We’ll hear more about Erin’s research shortly. But first, let’s step into a sleep lab.

For 40 years, the sleep lab was the prime way to study dreaming. That’s where Allan Hobson began his investigations of the dreaming brain in the 1960s.

Allan Hobson : “We had a patient room, a subject room, in which the subject was attached to electrodes, and the electrodes went through the wall. And we sat in a room next door and recorded the brain waves, and when the subjects entered REM or another stage that interested us, we’d wake them up and try to figure out what was going on.”

When they woke their subjects up, they asked them for a “dream report.” Dream reports were nothing new; psychologists and psychiatrists had been asking patients to recount their dreams since Freud. But these earlier reports might be made days, weeks or months after the actual dream took place, with patients choosing to relate only the most memorable of their dreams or perhaps being steered towards particular recollections by their interrogator. Hobson wanted to make dream reports more scientific.

Allan Hobson : “I was becoming aware that what was really needed was a much more quantitative approach to a subjective activity, and that’s why I developed the scoring system that I developed.”

Hobson’s scoring system was a way to record and quantify the content of people’s dreams, including the people who showed up in them, the places, plot continuity and so on.

Allan Hobson : “I think what you have to realize is that most people, including scientists, just didn’t do that. To do that is to create a science instead of a speculative psychology.”

Content analysis by researchers such as William Domhoff , whose name we’ll hear again later, showed that although dreams can seem bizarre, mostly they feature people who are known to us, places that are familiar to us and everyday activities that we perform in our waking lives, as well as things that are on our mind. So a tennis player is likely to dream about playing tennis, maybe with a friend or a family member. While a skier will probably not be playing tennis in her dream, but might be rehearsing downhill turns. These findings might not sound groundbreaking, but in the 1960s and ’70s, every discovery was important because so little was known about dreaming. Here’s Ursula Voss , a psychologist who collaborated with Hobson on more recent studies of dreaming.

Ursula Voss : “I admire the most about these early studies that they didn’t really have a strong hypothesis in one or the other direction, so their research was mostly exploratory. No matter what they found, it was important. And so in my view it’s very reliable and very objective research.”

By the late 1970s researchers had a good understanding of what people dream about.

The question of why we dream was more difficult to answer.

Nevertheless, a 1978 review of sleep and dreams did attempt to address this question. The second half, on dreaming, was written by Rosalind Cartwright. As one of the first women to work in this area, she was often called the “queen of dreams.” Officially she was a psychologist who ran a sleep lab at the University of Illinois, and then for many years at Rush University. In the 1978 review, Cartwright begins by lamenting our lack of understanding, despite now having the tools to study dreams:

It is the syntax and grammar of dreams as cognitive behavior, their meaning and function in relation to other types of cognitive activity of sleep and waking, and their place in our understanding of human behavior more generally that has lagged behind.

The trouble with theories about the function of dreams is that they are difficult to test. One theory that caught Cartwright’s attention is that dreams help us to “assimilate anxiety.” A couple of studies had been done on this, and...

The results of none of these studies is strong and convincing in and of themselves, but all lend some support to the hypothesis that when dreaming is intact in normal persons, waking situations which were previously emotion-evoking are faced more directly and handled more calmly…

Cartwright was intrigued and designed her own experiment to test the theory. She found 29 women undergoing divorce and studied them in her sleep lab for six nights. The women were divided into two groups: depressed and not depressed — and compared to a group of happily married women. In 1984, she published her findings in the journal Psychiatry :

The dreams of those divorcing without major mood upset were longer and dealt with a wider time frame than those of the other two groups. They also dealt with marital status issues which were absent in the dreams of the depressed group.

Cartwright concluded that dreams can act as overnight therapy, a night shift designed to help us process difficult emotions.

This idea has been brought up to date by recent studies looking at chemical changes in the brain, as well as studies using magnetic resonance imaging, MRI, to see which areas of the brain are most active at different stages of sleep. The findings from these studies were summarized in a 2014 review called “ The Role of Sleep in Emotional Brain Function ”:

Neuroimaging studies reveal significant activity increases during REM sleep in emotion-related regions… These changes in functional brain activity are paralleled (and likely governed by) striking alterations in neurochemistry. Perhaps most remarkable is a substantial reduction in levels of noradrenaline during REM sleep…

Noradrenaline, also known as norepinephrine, is one of the body’s “fight or flight” chemicals. It makes us alert, restless, maybe anxious. It prepares us for action. Irregular levels of noradrenaline are associated with PTSD and major depression.

REM sleep may serve a noradrenergic “housekeeping” function, one that reduces and thus restores concentrations of noradrenaline to baseline each day… allowing for optimal wakeful functioning.

If we don’t get enough REM sleep, as is common among people with PTSD, who fear experiencing flashbacks in their dreams, then our noradrenaline levels aren’t reset properly and we may wake up in a hyper-vigilant, restless state.

These are intriguing findings about REM sleep. But it’s difficult to know exactly what role dreaming plays, because although we can record how much REM sleep someone has, or check their noradrenaline levels, we can’t know for sure how much they are dreaming.

Another theory about why we dream is that dreams help us to consolidate memories. This is what Erin Wamsley studies at Furman University in South Carolina.

Erin Wamsley : “Well, we know that when animals — and apparently humans — fall asleep, patterns of brain activity that were first established when we had a recent experience, are then reactivated or replayed in the sleeping brain. For example, in rodent studies, we see that when a rat is moving through a track — like moving through a maze — you can describe their movement through the maze in terms of a sequence of cells firing: Cell 5, Cell 8, Cell 7. And then when the animal falls asleep, we again see: Cell 5, Cell 8, Cell 7. Cell 5, Cell 8, Cell 7 — but played back in a speeded, time-compressed manner. We haven’t seen exactly that in humans, but still, when humans do a learning task in wakefulness, you can measure patterns of brain activity occurring during that task and see that those patterns of brain activity that occurred during the learning task are again present when the human falls asleep.”

We also know that we dream about our experiences — that’s one of the things that the early content analysis studies told us. Erin Wamsley : “And then our work has actually shown that when you dream of something you learned recently, people who dream about that experience improve their memory more, compared to people who do not report remembering a dream about the experience. So all that put together, I would say the most plausible explanation is that, at least part of the content of dreams is reflecting this memory-related brain activity, right? I can’t say for sure whether dreams are helping your memory, because we don’t know if it’s important that you consciously experience it; it could be just a side effect.”

Even if it’s not just a side effect — and that’s a difficult thing to test — Erin Wamsley doesn’t think that strengthening memories explains the whole function of dreaming. And Hobson agreed that memory processing is probably only part of the explanation.

Besides, the bizarre scenes that can unfold in our dreams, they aren’t like memories, says Antti Revonsuo , a Finnish philosopher and neuroscientist.

Antti Revonsuo : “What we dream about, they are not our memories. It’s always in the present, it’s novel, it’s creative, it’s original experience, rather than a memory.”

So what other theories are there?

How often are you scared in your dreams? Are you running away from something?

Antti Revonsuo thinks that dreams are a way for us to rehearse potentially threatening situations in order to aid our survival. He calls this the threat simulation theory of dreaming.

Antti Revonsuo : “The most universal topics of dreams are like primitive threat simulations, like being chased, being attacked, and also modern types of threats: You lose your wallet, your phone, the elevator doesn’t work, you are late from the plane — and everybody recognizes this. So I started to realize that the data actually points to this direction.”

Content analysis of dreams by Revonsuo’s research group and others backs this up.

Antti Revonsuo : “In the normal population, it’s usually about two-thirds of dream reports that contain at least one threatening event. The number is usually between 65 to 70 percent of dream reports.”

So the threat simulation theory could explain many of our dreams. But what about dreams that aren’t nightmares or even mildly threatening? How does Revonsuo explain those dreams?

Antti Revonsuo : “I ended up proposing together with my colleagues what we call the social simulation theory, and the basic idea there is that the kind of non-threatening dreams, that what we are rehearsing there, is like social perception, social interaction, social bonding. And this is based on what we now know, as well, if we quantify this kind of social content of dreams, there is also a bias for dreams to contain more social events than our waking lives.”

So far we’ve heard that dreams might help us to rehearse social situations or threatening events, that they might be the product of our brain’s memory processing system, and that they might help us to deal with our emotions.

But not all sleep researchers sign up to one of these theories. In fact, some think that dreams have no biological function at all. William Domhoff, who’s been studying dreams for over five decades, proposes that dreaming is just an accidental byproduct of the brain in sleep mode. Could the complex, vivid imaginings that we all experience every night be a mere side effect, an accident of evolution? Some find that hard to buy. As Allan Rechtschaffen , another longtime sleep researcher, put it in a well-known quote: “If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.”

What have we learnt then, from over 60 years of studying dreaming? Is there any agreement on the what, when and why of dreaming?

We’ve learnt that dreams reflect our waking experiences, with the same people, places and concerns popping up in them — even if they’re mixed up.

We now know that we dream a lot more than we once thought, and we dream during non-REM sleep as well as REM sleep. Here’s Erin Wamsley to explain:

Erin Wamsley : “So if you wake people up from rapid eye movement sleep, on average they might remember a dream around 80 percent of trials. And if you wake people up from non-rapid eye movement sleep, like Stage 2, they would maybe remember a dream around 50 percent of trials. It’s a quantitative difference. And the other differences between dreams and the two sleep stages are the same way. Actually, on average, REM dreams are longer and more vivid. And on average, non- REM dreams are shorter and less vivid, but those two distributions are overlapping. So it would be false to say we only have “real” dreams in REM sleep.”

But what progress have we made on the question of why we dream?

Erin Wamsley : “I don’t think there’s a consensus on what dreaming is, why we dream, what we do, what the function of dreaming is, or even if there is a function. But that being said, maybe some hypotheses from the past have now been ruled out by most people, which itself is a form of consensus and progress. So most psychologists and neuroscientists today have abandoned Freudian dream theory. And most neuroscientists and psychologists today view dreaming as having at least some substantial overlap with waking cognition, that some of the brain and mental processes are similar or overlapping between what we see generates thought and imagery and daydreaming in wakefulness, and what we see generates thought, imagery and daydreaming in sleep. Whereas in the past, there had been more a focus on sleep and dreaming are this crazy, mysterious thing that has nothing to do with being awake, and that was very Freud-influenced.”

So to understand dreaming, says Wamsley, we also need to understand how we generate thoughts and images when we’re awake — and that’s a big, complicated task. Undaunted, in his final years, Allan Hobson tried to synthesize everything he’d learnt about dreaming over his long career into a single theory that also accommodated this overlap between dreaming and our waking thoughts.

A dream is an experience of being present in an imaginary world. You might think of it as a virtual-reality world or a simulation of the world created by the brain. Being awake and conscious is also an experience of being a person in the world. Hobson began by proposing that we are all born with a virtual-reality model of the world in our heads. This innate or “genetic” model needs to be fine-tuned to fit the actual world that we live in and experience every day.

Allan Hobson : “I think you remake your model of the world every night in bed. You compare the genetic model with the experiential model, and you make such adjustments as you can. And you do that every single night.”

Hobson thought of this model of the world that we are born with as a prototype of consciousness. In fact, he thought that it’s there even before birth, when REM sleep becomes active in the fetus’s brain. This is the brain’s way of preparing itself for full consciousness. As we gain experience in the world, we refine our model — and that’s what we’re doing when we dream.

Hobson’s theory, which he called the protoconsciousness theory, can incorporate the idea that dreams and memories are linked, and it accommodates Revonsuo’s threat simulation theory of dreaming. So what does Revonsuo make of it?

Antti Revonsuo : “Well, I find the protoconscious theory, I find very, very interesting idea, and I have nothing against it. I think it would be consistent with any other simulation theories, but the problem with that theory is that it’s much harder to test.”

Still, Revonsuo agrees with Hobson that the dreaming brain is a route to understanding consciousness.

Antti Revonsuo : “Dreaming, we can take it as a model system of the basic form of consciousness. So our waking consciousness and dreaming consciousness, they are pretty much the same system, or highly overlapping systems, in the brain. It’s the same system that generates our being in the world experiencing both cases, and therefore to explain dreaming is to explain consciousness and vice versa. But dreaming is a better model system, because it really highlights the subjectivity of the phenomenon. Dreaming is a phenomenon that we cannot share. We can’t invite anybody into our dream world and say, “Yeah, I have these interesting dreams — please come and take a look.” So we can’t share dreams in any kind of empirical way. They are non-transmissible in some very fundamental manner. And that’s the problem with consciousness as well. Consciousness is subjective. And that’s the challenge for science. How can we do science on a phenomenon that is fundamentally experienced only by one person?”

This is a big shift in thinking. For a long time, most people imagined dreams as coming from outside of the dreamer’s own mind — they came from gods or other spiritual beings. Then Freud suggested that dreams are the product of our unconscious mind, writing:

The interpretation of dreams is the royal road to a knowledge of the unconscious activities of the mind.

But for scientists like Hobson and Revonsuo, dreams are the gateway not to our un conscious mind, but to consciousness itself. Revonsuo is happy that we finally seem to have an agreed definition of what dreams are, even if different theories emphasize different functions.

Antti Revonsuo : “We can say that now everybody is happy to say that, yeah, we can define dreaming as a world simulation or a virtual reality, that it takes into account that the idea that being in a dream feels like being in a world, basically. So nobody says that that’s somehow totally wrong. And then, this is just like the form of dreaming, then when we start to discuss the contents of dreaming, then maybe different theories emphasize different contents. And I’m very happy about that development, because this is kind of what I wanted to see — that the field actually moves forward.”

If you enjoyed this show, please share it with your friends, family and colleagues — we’d love to hear your feedback too. Tweet us @KnowableMag , write to us — we’re [email protected] — or leave us a review wherever you listen to podcasts. And don’t forget to subscribe so you don’t miss episodes on the search for extrasolar planets, the development of massive particle accelerators and our quest to treat depression.

In this episode you heard from Allan Hobson, Erin Wamsley, Ursula Voss and Antti Revonsuo. The episode also featured quotes from three articles published by Annual Reviews. They are: Harold Williams et al ., 1973; Wilse Webb and Rosalind Cartwright , 1978; Andrea Goldstein and Matthew Walker , 2014. You can find links to those papers and others mentioned in this podcast in the show notes on our website: knowablemagazine.org/podcast .

This podcast was produced by Knowable Magazine , a nonprofit publication that seeks to make scientific knowledge accessible to all. Knowable Magazine is an editorially independent initiative from Annual Reviews. Explore more sound science and smart stories at knowablemagazine.org .

I’m Charlotte Stoddart and this has been Knowable .

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States of Consciousness

Dreams and Dreaming

Learning objectives.

Describe and differentiate between theories on why we dream

The meaning of dreams varies across different cultures and periods of time. By the late 19th century, German psychiatrist Sigmund Freud had become convinced that dreams represented an opportunity to gain access to the unconscious. By analyzing dreams, Freud thought people could increase self-awareness and gain valuable insight to help them deal with the problems they faced in their lives. Freud made distinctions between the manifest content and the latent content of dreams.

Manifest content is the actual content, or storyline, of a dream. Latent content , on the other hand, refers to the hidden meaning of a dream. For instance, if a woman dreams about being chased by a snake, Freud might have argued that this represents the woman’s fear of sexual intimacy, with the snake serving as a symbol of a man’s penis.

Freud was not the only theorist to focus on the content of dreams. The 20th century Swiss psychiatrist Carl Jung believed that dreams allowed us to tap into the collective unconscious . The collective unconscious, as described by Jung, is a theoretical repository of information he believed to be shared by everyone. According to Jung, certain symbols in dreams reflected universal archetypes with meanings that are similar for all people regardless of culture or location.

The sleep and dreaming researcher Rosalind Cartwright, however, believes that dreams simply reflect life events that are important to the dreamer. Unlike Freud and Jung, Cartwright’s ideas about dreaming have found empirical support. For example, she and her colleagues published a study in which women going through divorce were asked several times over a five month period to report the degree to which their former spouses were on their minds. These same women were awakened during REM sleep in order to provide a detailed account of their dream content. There was a significant positive correlation between the degree to which women thought about their former spouses during waking hours and the number of times their former spouses appeared as characters in their dreams (Cartwright, Agargun, Kirkby, & Friedman, 2006). Recent research (Horikawa, Tamaki, Miyawaki, & Kamitani, 2013) has uncovered new techniques by which researchers may effectively detect and classify the visual images that occur during dreaming by using fMRI for neural measurement of brain activity patterns, opening the way for additional research in this area.

Recently, neuroscientists have also become interested in understanding why we dream. For example, Hobson (2009) suggests that dreaming may represent a state of protoconsciousness. In other words, dreaming involves constructing a virtual reality in our heads that we might use to help us during wakefulness. Among a variety of neurobiological evidence, John Hobson cites research on lucid dreams as an opportunity to better understand dreaming in general. Lucid dreams are dreams in which certain aspects of wakefulness are maintained during a dream state. In a lucid dream, a person becomes aware of the fact that they are dreaming, and as such, they can control the dream’s content (LaBerge, 1990).

Theories on Dreaming

While the Freudian theory of dreaming may be the most well known, and Cartwright’s suggestions on dreaming the most plausible, there are several other theories about the purpose of dreaming. The threat-simulation theory suggests that dreaming should be seen as an ancient biological defense mechanism. Dreams are thought to provide an evolutionary advantage because of their capacity to repeatedly simulate potential threatening events. This process enhances the neurocognitive mechanisms required for efficient threat perception and avoidance.

The expectation-fulfillment theory posits that dreaming serves to discharge emotional arousals (however minor) that haven’t been expressed during the day. This practice frees up space in the brain to deal with the emotional arousals of the next day and allows instinctive urges to stay intact. In effect, the expectation is fulfilled (the action is “completed”) in a metaphorical form so that a false memory is not created. This theory explains why dreams are usually forgotten immediately afterwards.

One prominent neurobiological theory of dreaming is the activation-synthesis theory , which states that dreams don’t actually mean anything. They are merely electrical brain impulses that pull random thoughts and imagery from our memories. The theory posits that humans construct dream stories after they wake up, in a natural attempt to make sense of the nonsensical. However, given the vast documentation of the realistic aspects of human dreaming, as well as indirect experimental evidence that other mammals such as cats also dream, evolutionary psychologists have theorized that dreaming does indeed serve a purpose.

The continual-activation theory proposes that dreaming is a result of brain activation and synthesis. Dreaming and REM sleep are simultaneously controlled by different brain mechanisms. The hypothesis states that the function of sleep is to process, encode, and transfer data from short-term memory to long-term memory through a process called consolidation. However, there is not much evidence to back this up. NREM sleep processes the conscious-related memory (declarative memory), and REM sleep processes the unconscious related memory (procedural memory).

The underlying assumption of continual-activation theory is that, during REM sleep, the unconscious part of the brain is busy processing procedural memory. Meanwhile, the level of activation in the conscious part of the brain descends to a very low level as the inputs from the senses are basically disconnected. This triggers the “continual-activation” mechanism to generate a data stream from the memory stores to flow through to the conscious part of the brain.

Link to Learning

Review the purpose and stages of sleep as well as the reasons why we dream in the following CrashCourse video:

You can view the transcript for “To Sleep, Perchance to Dream: Crash Course Psychology #9” here (opens in new window) .

CC licensed content, Original

Modification, adaptation, and original content. Provided by : Lumen Learning. License : CC BY: Attribution

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Stages of Sleep. Authored by : OpenStax College. Located at : https://openstax.org/books/psychology-2e/pages/4-3-stages-of-sleep . License : CC BY: Attribution . License Terms : Download for free at https://openstax.org/books/psychology-2e/pages/1-introduction
The Nature and Meaning of Dreams. Provided by : Boundless. Located at : https://www.boundless.com/psychology/textbooks/boundless-psychology-textbook/states-of-consciousness-6/sleep-and-dreaming-42/the-nature-and-meaning-of-dreams-184-12719/ . License : CC BY-SA: Attribution-ShareAlike
Sleeping woman. Authored by : Craig Adderley. Provided by : Pexels. Located at : https://www.pexels.com/photo/woman-sleeping-1497855/ . License : CC0: No Rights Reserved

To Sleep, Perchance to Dream – Crash Course Psychology #9. Provided by : CrashCourse. Located at : https://www.youtube.com/watch?v=rMHus-0wFSo . License : Other . License Terms : Standard YouTube License

storyline of events that occur during a dream, per Sigmund Freud’s view of the function of dreams

hidden meaning of a dream, per Sigmund Freud’s view of the function of dreams

common psychological tendencies that have been passed down from one generation to the next

people become aware that they are dreaming and can control the dream’s content

suggests that dreaming should be seen as an ancient biological defense mechanism that provides an evolutionary advantage because of its capacity to repeatedly simulate potential threatening events, thus enhancing the mechanisms required for efficient threat avoidance.

states that dreams don't actually mean anything. Instead, dreams are merely electrical brain impulses that pull random thoughts and imagery from our memories.

proposes that dreaming is a result of brain activation and synthesis; its assumption is that, during REM sleep, the unconscious part of the brain is busy processing procedural memory

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Why Do We Dream? (6 Theories and Psychological Reasons)

Psychologists, scientists, and even spiritual leaders have built theories around why we dream. While not all these theories are accepted anymore, the true nature of why we dream is a mystery. What we do know is that dreams can benefit us in many ways!

Theories about why we have dreams include:

Ancient theories
Freud's Wish-Fulfillment Theory

Activation-Synthesis Theory

Threat- and Social-Simulation Theory
Information-Processing Theory (Self-Organization Model)

Physiological-Functioning Theory

Ancient and freudian theories of dreaming.

"Why do we dream?" is a question that people have been asking since the dawn of time. In the earliest days of the study or contemplation of dreams, dreams had serious meaning. Humans are meaning-making creatures, so it's natural for us to have a dream and ask "what does this mean?"

In the Bible, for example, dreams are often portrayed as messages from God. Mesopotamian kings took advice from their dreams. Ancient Egyptians wrote dream interpretations and what specific dreams meant for the dreamer. Medieval Europeans also wrote down how to interpret certain dreams.

Ancient cultures laid the foundation of this work, but one name is synonymous with dream interpretation: Sigmund Freud .

Wish-Fulfillment

Sigmund Freud, like many people, asked himself, "Why do we dream?" He believed he discovered the answer after, you guessed it, a dream. After dreaming about a patient whom he felt he had failed, Freud created the wish-fulfillment theory.

Freud's wish-fulfillment theory suggests that we dream to fulfill repressed wishes. Often, these wishes are embarrassing. We wish to kill our father or have sex with our mother, for example. (Freud has some interesting theories.) That's why, Freud believed, our dreams were so bizarre. We added unique elements so we could still fulfill our wish but in a more palatable way. In Freud's The Interpretation of Dreams , he interprets these unique elements. For example, he suggests interactions with sticks, trees, and other phallic-shaped items suggest...you can probably guess.

Freud's theories of dream interpretation and wish fulfillment are not accepted anymore. They have since been replaced by a variety of other theories about why we dream and how it benefits the dreamer.

When Do We Dream?

Before diving into more modern theories about why we dream, you should know when we dream. Dreaming takes place in the REM stage of sleep, or "rapid eye movement" stage. This name suggests exactly what happens during this stage. Although the rest of the body is close to paralyzation, our eyes rapidly move back and forth. The heart rate and breathing increase.

Brain activity is also especially high during REM sleep. REM sleep is crucial for the mind to recuperate, while other stages of sleep are vital for the body to do the same.

Knowing this, let's dive into why modern psychologists think we dream.

Remember when I said that humans are "meaning-making creatures?" Well, J. Allan Hobson and Robert McCarley took that into consideration. In 1977, they created the Activation-Synthesis Theory.

The Activation-Synthesis Theory suggests that dreams are the result of our brains attempting to make meaning from the brain activity that takes place during sleep. These dreams aren't meaningless, necessarily, but they do not come from unconscious wishes or messages from the beyond. Just as we daydream to make sense of our social interactions, we dream to make sense of all the neurons firing in our brains during sleep.

Information-Processing Theory and the Self-Organization Model

Similarly, information-processing theory suggests dreams are just a part of our cognitive development. Cognitive psychology looks at how the brain makes decisions, solves problems, and stores memories. Memory storage is key to this study and why we dream.

Dreaming could just be a key part of how we convert our short-term memories into long-term memory. And our minds don't shove all long-term memories into one big storage container. Information-processing theory suggests that we organize our memories as we sleep. Our dreams, which often contain elements from what we experienced that day, are a byproduct of that process.

To illustrate this, psychologists developed the Self-Organization Model . While this model does not address the content of dreams itself, it looks at how dreams are formed.

Threat-Simulation and Social-Simulation Theory

A lot of dream theories explain why we might have nonsensical, yet pleasant, dreams. But what about nightmares? Why do we dream that we're fired from our job, dumped by our partner, or taking a test without any pants on? Threat-simulation theory has a guess.

Finnish neuroscientist Antti Revonsuo suggested that nightmares are actually a biological defense mechanism . We simulate threats in our dreams so that we may be more prepared for them if we actually face them. Revonsuo theorized that the ancient humans that did "practice" facing these threats could fight them off and have children. Those children, too, simulated threats in their dreams and were more prepared to fight them.

The threats we face today are very different than what early humans faced. (We discuss this often when discussing fight-or-flight.) Whereas "threats" used to be carnivorous animals, now our bodies get just as stressed by pop quizzes and asking a cute girl out to the dance.

Social-Simulation Theory

Could it be that all dreams, nightmarish or not, are practice? Some say yes! The social-simulation theory of dreaming suggests that all dreams are a defense mechanism of sorts. When we practice social situations, we are more prepared for them.

How many times do you prepare for a conversation with a friend, partner, or boss? Dreams are just our unconscious way of doing the same thing!

One last theory about why we dream is known as the physiological-functioning theory. This theory suggests that dreams are pretty much meaningless and that we dream to preserve neural pathways. Have you ever been told to run your car for ten minutes once a week to keep it working properly? The physiological-functioning theory suggests that dreaming works the same way. We spend a lot of time sleeping. Brain activity during this time keeps us functioning and ready to process information when we wake up the next morning!

Physiological-functioning theor y was supported in a 2009 paper written by J. Allan Hobson.

Yes, the same J. Allan Hobson who wrote about activation-synthesis theory. Hobson has been a sleep researcher at Harvard for many years now. While he continues to assert that dreams are not some divine message, he has shifted his thoughts on why we dream.

Which Theory is Correct?

The answer to the question "why do we dream" is like the answer to many deep questions in psychology and biology. It's always evolving. The theories on this page are just the more popular theories that exist in psychology today! There are other theories, we dream to forget or to respond to what is happening in the outside world as we sleep. We cannot say for sure why we dream. With the help of modern theories and the creativity of ancient theories, we continue to get closer to the answer.

Why Do We Have Sleep Paralysis?

If you have ever experienced sleep paralysis, you know that it's one of the scariest "dreams" you can have. Sleep paralysis occurs when you think you are awake and conscious but have no control of your body and no ability to move. People in sleep paralysis might even try sleeping with no success. "Sleep paralysis demons" and other people may exist in your room as you experience sleep paralysis, only to disappear when you actually wake up.

This sounds terrifying, and it is. Around 1 in 10 people have experienced this type of "dream," and few claim to have a pleasant experience with it. (If you endure sleep paralysis enough, however, you can determine when it's happening and "ride out" the sensation of not being able to move.)

Why does this happen? Psychologists don't have a theory for this, but neurologists do have an explanation.

REM and Non-REM Sleep

There are two phases of sleep: rapid eye movement (REM) sleep and non-REM sleep. We dream during REM sleep, but something else also happens. Chemicals in the brain essentially "shut down" our bodies, putting us into paralysis. (The only thing that is moving during this time is the eyes, hence the name "rapid eye movement.") This happens so that we don't act out our dreams. Typically, the body moves through various phases of REM and non-REM sleep throughout the night, ending in a non-REM "light" sleep that transitions us back to wakefulness.

Sleep paralysis occurs when the mind is awake, but the body is still in REM sleep. Essentially, you are paralyzed, but just for a short period of time.

What Causes Sleep Paralysis?

There is no one cause of sleep paralysis. Studies have found that young adults are most likely to experience it. Some studies suggest that genetics make people more prone to sleep paralysis, but not enough research has been done to say this definitively. Sleeping on your back is more likely to cause sleep paralysis.

Other factors, like irregular sleep schedules and high stress, may also attribute to sleep paralysis. If you are experiencing sleep paralysis, take a look at your routine before and after sleeping. Are you drinking alcohol? Do you sleep at the same time every night? Practice healthy sleeping habits and you may eliminate sleep paralysis while gaining many other health benefits.

Why Do We Remember Our Dreams?

Dreams don't stick in our memories for a long period of time. We may wake up and write down our dreams, but unless they are recalled early in the day, we are likely to forget them. Sometimes, we don't "have dreams" at all. Why does this occur?

The answer, not surprisingly, goes back to the stages of sleep. On an ideal night, our body cycles through many sleep stages: light, deep, REM sleep, deep, light, and deep again. The cycle continues until we have reached a period of light sleep that transitions us to wakefulness. In this ideal scenario, we are unlikely to forget our dreams. (And our mornings are much more pleasant!)

It's possible to wake up every morning while in a light sleep stage, even if you set an alarm or don't get a full eight hours of sleep. Apps and different software can help you wake up each morning at "the right time." But not everyone wakes up naturally from a light sleep. Alarms, kids, and other disruptions may yank you out of sleep while you were in REM sleep. When this happens, you are most likely to remember your dreams.

If your dreams interest you, keep a notebook nearby! Write down any key details from your dreams and how you felt in the morning. Even though Freud's dream interpretations are not widely accepted anymore, a mental health counselor can help you "interpret" your dreams. Therapists may be able to pick up on patterns that they notice and tie it back to any sources of stress in your waking life.

Activation Synthesis Theory
Sleep Stages (Light, Deep, REM)
Why Do My Dreams Feel Real?
Why Can't You Wake Up A Sleepwalker? (Reasons + Myths)
Insight Learning (Definition+ 4 Stages + Examples)

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Dreams and Dreaming

Dreams and dreaming have been discussed in diverse areas of philosophy ranging from epistemology to ethics, ontology, and more recently philosophy of mind and cognitive science. This entry provides an overview of major themes in the philosophy of sleep and dreaming, with a focus on Western analytic philosophy, and discusses relevant scientific findings.

1.1 Cartesian dream skepticism

1.2 earlier discussions of dream skepticism and why descartes’ version is special, 1.3 dreaming and other skeptical scenarios, 1.4 descartes’ solution to the dream problem and real-world dreams, 2.1 are dreams experiences, 2.2 dreams as instantaneous memory insertions, 2.3 empirical evidence on the question of dream experience, 2.4 dreams and hallucinations, 2.5 dreams and illusions, 2.6 dreams as imaginative experiences, 2.7 dreaming and waking mind wandering, 2.8 the problem of dream belief, 3.1 dreaming as a model system and test case for consciousness research, 3.2 dreams, psychosis, and delusions, 3.3 beyond dreams: dreamless sleep experience and the concepts of sleep, waking, and consciousness, 4. dreaming and the self, 5. immorality and moral responsibility in dreams, 6.1 the meaning of dreams, 6.2 the functions of dreaming, 7. conclusions, other internet resources, related entries, 1. dreams and epistemology.

Dream skepticism has traditionally been the most famous and widely discussed philosophical problem raised by dreaming (see Williams 1978; Stroud 1984). In the Meditations , Descartes uses dreams to motivate skepticism about sensory-based beliefs about the external world and his own bodily existence. He notes that sensory experience can also lead us astray in commonplace sensory illusions such as seeing things as too big or small. But he does not think such cases justify general doubts about the reliability of sensory perception: by taking a closer look at an object seen under suboptimal conditions, we can easily avoid deception. By contrast, dreams suggest that even in a seemingly best-case scenario of sensory perception (Stroud 1984), deception is possible. Even the realistic experience of sitting dressed by the fire and looking at a piece of paper in one’s hands (Descartes 1641: I.5) is something that can, and according to Descartes often does, occur in a dream.

There are different ways of construing the dream argument. A strong reading is that Descartes is trapped in a lifelong dream and none of his experiences have ever been caused by external objects (the Always Dreaming Doubt ; see Newman 2019). A weaker reading is that he is just sometimes dreaming but cannot rule out at any given moment that he is dreaming right now (the Now Dreaming Doubt ; see Newman 2019). This is still epistemologically worrisome: even though some of his sensory-based beliefs might be true, he cannot determine which these are unless he can rule out that he is dreaming. Doubt is thus cast on all of his beliefs, making sensory-based knowledge slip out of reach.

Cartesian-style skeptical arguments have the following form (quoted from Klein 2015):

If I know that p , then there are no genuine grounds for doubting that p .
U is a genuine ground for doubting that p .
Therefore, I do not know that p .

If we apply this to the case of dreaming, we get:

If I know that I am sitting dressed by the fire, then there are no genuine grounds for doubting that I am really sitting dressed by the fire.
If I were now dreaming, this would be a genuine ground for doubting that I am sitting dressed by the fire: in dreams, I have often had the realistic experience of sitting dressed by the fire when I was actually lying undressed in bed!
Therefore, I do not know that I am now sitting dressed by the fire.

Importantly, both strong and weak versions of the dream argument cast doubt only on sensory-based beliefs, but leave other beliefs unscathed. According to Descartes, that 2+3=5 or that a square has no more than 4 sides is knowable even if he is now dreaming:

although, in truth, I should be dreaming, the rule still holds that all which is clearly presented to my intellect is indisputably true. (Descartes 1641: V.15)

By Descartes’ lights, dreams do not undermine our ability to engage in the project of pure, rational enquiry (Frankfurt 1970; but see Broughton 2002).

Dream arguments have been a staple of philosophical skepticism since antiquity and were so well known that in his objections to the Meditations , Hobbes (1641) criticized Descartes for not having come up with a more original argument. Yet, Descartes’ version of the problem, more than any other, has left its mark on the philosophical discussion.

Earlier versions tended to touch upon dreams just briefly and discuss them alongside other examples of sensory deception. For example, in the Theaetetus (157e), Plato has Socrates discuss a defect in perception that is common to

dreams and diseases, including insanity, and everything else that is said to cause illusions of sight and hearing and the other senses.

This leads to the conclusion that knowledge cannot be defined through perception.

Dreams also appear in the canon of standard skeptical arguments used by the Pyrrhonists. Again, dreams and sleep are just one of several conditions (including illness, joy, and sorrow) that cast doubt on the trusthworthiness of sensory perception (Diogenes Laertius, Lives of Eminent Philosophers; Sextus Empiricus, Outlines of Pyrrhonism) .

Augustine ( Against the Academics ; Confessions) thought the dream problem could be contained, arguing that in retrospect, we can distinguish both dreams and illusions from actual perception (Matthew 2005: chapter 8). And Montaigne ( The Apology for Raymond Sebond ) noted that wakefulness itself teems with reveries and illusions, which he thought were even more epistemologically worrisome than nocturnal dreams.

Descartes devoted much more space to the discussion of dreaming and cast it as a unique epistemological threat distinct from both waking illusions and evil genius or brain-in-a-vat-style arguments. His claim that he has often been deceived by his dreams implies he also saw dreaming as a real-world (rather than merely hypothetical) threat.

This is further highlighted by the intimate, first-person style of the Meditations . Their narrator is supposed to exemplify everyone’s epistemic situation, illustrating the typical defects of the human mind. Readers are further drawn in by Descartes’ strategy of moving from commonsense examples towards more sophisticated philosophical claims (Frankfurt 1970). For example, Descartes builds up towards dream skepticism by first considering familiar cases of sensory illusions and then deceptively realistic dreams.

Finally, much attention has been devoted to several dreams Descartes reportedly had as a young man. Some believe these dreams embodied theoretical doubts he developed in the Discourse and Meditations (Baillet 1691; Leibniz 1880: IV; Cole 1992; Keefer 1996). Hacking (2001:252) suggests that for Descartes, dream skepticism was not just a philosophical conundrum but a source of genuine doubt. There is also some discussion about the dream reports’ authenticity (Freud 1940; Cole 1992; Clarke 2006; Browne 1977).

In the Meditations , after discussing the dream argument, Descartes raises the possibility of an omnipotent evil genius determined to deceive us even in our most basic beliefs. Contrary to dream deception, Descartes emphasizes that the evil genius hypothesis is a mere fiction. Still, it radicalizes the dream doubt in two respects. One, where the dream argument left the knowability of certain general truths intact, these are cast in doubt by the evil genius hypothesis . Two, where the dream argument, at least on the weaker reading, involves just temporary deception, the evil genius has us permanently deceived.

One modernized version, the brain-in-a-vat thought experiment, says that if evil scientists placed your brain in a vat and stimulated it just right, your conscious experience would be exactly the same as if you were still an ordinary, embodied human being (Putnam 1981). In the Matrix -trilogy (Chalmers 2005), Matrixers live unbeknownst to themselves in a computer simulation. Unlike the brain-in-a-vat , they have bodies that are kept alive in pods, and flaws in the simulation allow some of them to bend its rules to their advantage.

Unlike dream deception, which is often cast as a regularly recurring actuality (cf. Windt 2011), brain-in-a-vat-style arguments are often thought to be merely logically or nomologically possible. However, there might be good reasons for thinking that we actually live in a computer simulation (Bostrom 2003), and if we lend some credence to radical skeptical scenarios, this may have consequences for how we act (Schwitzgebel 2017).

Even purely hypothetical skeptical scenarios may enhance their psychological force by capitalizing on the analogy with dreams. Clark (2005) argues that the Matrix contains elements of “industrial-strength deception” in which both sensory experience and intellectual functioning are exactly the same as in standard wake-states, whereas other aspects are more similar to the compromised reasoning and bizarre shifts that are the hallmark of dreams.

At the end of the Sixth Meditation , Descartes suggests a solution to the dream problem that is tied to a reassessment of what it is like to dream. Contrary to his remarks in the First Meditation , he notes that dreams are only rarely connected to waking memories and are often discontinuous, as when dream characters suddenly appear or disappear. He then introduces the coherence test:

But when I perceive objects with regard to which I can distinctly determine both the place whence they come, and that in which they are, and the time at which they appear to me, and when, without interruption, I can connect the perception I have of them with the whole of the other parts of my life, I am perfectly sure that what I thus perceive occurs while I am awake and not during sleep. (Meditation VI. 24)

For all practical purposes, he has now found a mark by which dreaming and waking can be distinguished (cf. Meditation I.7), and even if the coherence test is not fail-safe, the threat of dream deception has been averted.

Descartes’ remarks about the discontinuous and ad hoc nature of many dreams are backed up by empirical work on dream bizarreness (see Hobson 1988; Revonsuo & Salmivalli 1995). Still, many of his critics were not convinced this helped his case against the skeptic. Even if Descartes’ revised phenomenological description characterizes most dreams, one might occasionally merely dream of successfully performing the test (Hobbes 1641), and in some dreams, one might seem to have a clear and distinct idea but this impression is false (Bourdin 1641). Both the coherence test and the criterion of clarity and distinctness would then be unreliable.

How considerations of empirical plausibility impact the dream argument continues to be a matter of debate. Grundmann (2002) appeals to scientific dream research to introduce an introspective criterion: when we introspectively notice that we are able to engage in critical reflection, we have good reason to think that we are awake and not dreaming. However, this assumes critical reasoning to be uniformly absent in dreams. If attempts at critical reasoning do occur in dreams and if they generally tend to be corrupted, the introspective criterion might again be problematic (Windt 2011, 2015a). There are also cases in which even after awakening, people mistake what was in fact a dream for reality (Wamsley et al. 2014). At least in certain situations and for some people, dream deception might be a genuine cause of concern (Windt 2015a).

2. The ontology of dreams

In what follows, the term “conscious experience” is used as an umbrella term for the occurrence of sensations, thoughts, impressions, emotions etc. in dreams (cf. Dennett 1976). These are all phenomenal states: there is something it is like to be in these states for the subject of experience (cf. Nagel 1974). To ask about dream experience is to ask whether it is like something to dream while dreaming, and whether what it is like is similar to (or relevantly different from) corresponding waking experiences.

Cartesian dream skepticism depends on a seemingly innocent background assumption: that dreams are conscious experiences. If this is false, then dreams are not deceptive experiences during sleep and we cannot be deceived, while dreaming, about anything at all. Whether dreams are experiences is a major question for the ontology of dreams and closely bound up with dream skepticism.

The most famous argument denying that dreams are experiences was formulated by Norman Malcolm (1956, 1959). Today, his position is commonly rejected as implausible. Still, it set the tone for the analysis of dreaming as a target phenomenon for philosophy of mind.

For Malcolm, the denial of dream experience followed from the conceptual analysis of sleep: “if a person is in any state of consciousness it logically follows that he is not sound asleep” (Malcolm 1956: 21). Following some remarks of Wittgenstein’s (1953: 184; see Chihara 1965 for discussion), Malcolm claimed

the concept of dreaming is derived, not from dreaming, but from descriptions of dreams, i.e., from the familiar phenomenon that we call “telling a dream”. (Malcolm 1959:55)

Malcolm argued that retrospective dream reports are the sole criterion for determining whether a dream occurred and there is no independent way of verifying dream reports. While first-person, past-tense psychological statements (such as “I felt afraid”) can at least in principle be verified by independent observations (but see Canfield 1961; Siegler 1967; Schröder 1997), he argued dream reports (such as “in my dream, I felt afraid”) are governed by different grammars and merely superficially resemble waking reports. In particular, he denied dream reports imply the occurrence of experiences (such as thoughts, feelings, or judgements) in sleep:

If a man had certain thoughts and feelings in a dream it no more follows that he had those thoughts and feelings while asleep, than it follows from his having climbed a mountain in a dream that he climbed a mountain while asleep. (Malcolm 1959/1962: 51–52)

What exactly Malcolm means by “conscious experience” is unclear. Sometimes he seems to be saying that conscious experience is conceptually tied to wakefulness (Malcolm 1956); other times he claims that terms such as mental activity or conscious experience are vague and it is senseless to apply them to sleep and dreams (Malcolm 1959: 52).

Malcolm’s analysis of dreaming has been criticized as assuming an overly strict form of verificationism and a naïve view of language and conceptual change. A particularly counterintuitive consequence of his view is that there can be no observational evidence for the occurrence of dreams in sleep aside from dream reports. This includes behavioral evidence such as sleepwalking or sleeptalking, which he thought showed the person was partially awake; as he also thought dreams occur in sound sleep, such sleep behaviors were largely irrelevant to the investigation of dreaming proper. He also claimed adopting a physiological criterion of dreaming (such as EEG measures of brain activity during sleep) would change the concept of dreaming, which he argued was tied exclusively to dream reporting. This claim was particularly radical as it explicitly targeted the discovery of REM sleep and its association with dreaming (Dement & Kleitman 1957), which is commonly regarded as the beginning of the science of sleep and dreaming. Malcolm’s position was that the very project of a science of dreaming was misguided.

Contra Malcolm, most assume that justification does not depend on strict criteria with the help of which the truth of a statement can be determined with absolute certainty, but “on appeals to the simplicity, plausibility, and predictive adequacy of an explanatory system as a whole” (Chihara & Fodor 1965: 197). In this view, behavioral and/or physiological evidence can be used to verify dream reports (Ayer 1960) and the alleged principled difference between dream reports and other first-person, past-tense psychological sentences (Siegler 1967; Schröder 1997) disappears.

Putnam noted that Malcolm’s analysis of the concept of dreaming relies on the dubious idea that philosophers have access to deep conceptual truths that are hidden to laypeople:

the lexicographer would undoubtedly perceive the logical (or semantical) connection between being a pediatrician and being a doctor, but he would miss the allegedly “logical” character of the connection between dreams and waking impressions. […] this “depth grammar” kind of analyticity (or “logical dependence”) does not exist. (Putnam 1962 [1986]: 306)

Nagel argued that even if one accepts Malcolm’s analysis of the concept of dreaming,

it is a mistake to invest the demonstration that it is impossible to have experiences while asleep with more import than it has. It is an observation about our use of the word “experience”, and no more. It does not imply that nothing goes on in our minds while we dream. (Nagel 1959: 114)

Whether dream thoughts, feelings or beliefs should count as real instances of their kind now becomes an open question, and in any case there is no conceptual contradiction involved in saying one has experiences while asleep and dreaming.

To ask about dream experience is also to ask whether there is something it is like to dream during sleep as opposed to there just being something it is like to remember dreaming after awakening. Dennett’s (1976, 1979) cassette theory says dreams are the product of instantaneous memory insertion at the moment of the awakening, as if a cassette with pre-scripted dreams had been inserted into memory, ready for replay. Dennett claims the cassette theory and the view that dreams are experiences can deal equally well with empirical evidence for instance on the relationship between dreaming and REM sleep. The cassette theory is preferable because it is more parsimonious, positing only an unconscious dream composition process rather than an additional conscious presentation process in sleep. For Dennett, the important point is that it is impossible to distinguish between the two rival theories based on dream recall; the question of dream experience should be settled by independent empirical evidence.

While Dennett shares Malcolm’s skepticism about dream experience, this latter claim is diametrically opposed to Malcolm’s rejection of a science of dreaming. For Dennett, the unreliability of dream recall also is not unique, but exemplifies a broader problem with memory reports: we generally cannot use retrospective recall to distinguish conscious experience from memory insertion (Dennett 1991; see also Emmett 1978).

An earlier and much discussed (Binz 1878; Goblot 1896; Freud 1899; Hall 1981; Kramer 2007:22–24) version of Dennett’s cassette theory goes back to Maury’s (1861) description of a long and complex dream about the French revolution that culminated in his execution at the guillotine, at which point Maury suddenly awoke to find that the headboard had fallen on his neck. Because the dream seemed to systematically build up to this dramatic conclusion, which in turn coincided with a sudden external event, he suggested that such cases were best explained as instantaneous memory insertions experienced at the moment of awakening. Similarly, Gregory (1916) described dreams are psychical explosions occurring at the moment of awakening.

The trustworthiness of dream reports continues to be contentious. Rosen (2013) argues that dream reports are often fabricated and fail to accurately describe experiences occurring during sleep. By contrast, Windt (2013, 2015a) argues that dream reports can at least under certain conditions (such as in laboratory studies, when dreams are reported immediately after awakening by trained participants) be regarded as trustworthy sources of evidence with respect to previous experience during sleep.

Unlike Malcolm, many believe that whether dreams are experiences is an empirical question; and unlike Dennett, the predominant view is that the empirical evidence does indeed support this claim (Flanagan 2000; Metzinger 2003; Revonsuo 2006; Rosen 2013; Windt 2013, 2015a).

A first reason for thinking that dreams are experiences during sleep is the relationship between dreaming and REM (rapid eye movement) sleep. Researchers in the 1950s discovered that sleep is not a uniform state of rest and passivity, but there is a sleep architecture involving different stages of sleep that is relatively stable both within and across individuals (Aserinsky & Kleitman 1953, 1955; Dement & Kleitman 1957). Following sleep onset, periods of non-REM (or NREM) sleep including slow wave sleep (so called because of the presence of characteristic slow-wave, high-voltage EEG activity) are followed by periods of high-frequency, low-voltage activity during REM sleep. EEG measures from REM sleep strongly resemble waking EEG. REM sleep is additionally characterized by rapid eye movements and a near-complete loss of muscle tone (Dement 1999: 27–50; Jouvet 1999).

The alignment between conscious experience on the one hand and wake-like brain activity and muscular paralysis on the other hand would seem to support the experiential status of dreams as well as explain the outward passivity that typically accompanies them. Reports of dreaming are in fact much more frequent following REM (81.9%) than NREM sleep awakenings (43%; Nielsen 2000). REM reports tend to be more elaborate, vivid, and emotionally intense, whereas NREM reports tend to be more thought-like, confused, non-progressive, and repetitive (Hobson et al. 2000). These differences led to the idea that REM sleep is an objective marker of dreaming (Dement & Kleitman 1957; Hobson 1988: 154).

Attempts to identify dreaming with mental activity during REM sleep have not, however, been successful, and many now hold that dreams can occur in all stages of sleep (e.g., Antrobus 1990; Foulkes 1993b; Solms 1997, 2000; Domhoff 2003; Nemeth & Fazekas 2018). In recent years there has been renewed interest in NREM sleep for the study of dreaming (Noreika et al. 2009; Siclari et al. 2013, 2017). This suggests the inference from the physiology of REM sleep to the phenomenology of dreaming is not straightforward.

A second line of evidence comes from lucid dreams, or dreams in which one knows one is dreaming and often has some level of dream control (Voss et al. 2013; Voss & Hobson 2015; Baird et al. 2019). The term lucid dreaming was coined by van Eeden (1913), but Aristotle ( On Dreams ) already noted that one can sometimes be aware while dreaming that one is dreaming.

Scientific evidence that lucid dreaming is real and a genuine sleep phenomenon comes from laboratory studies (Hearne 1978; LaBerge et al. 1981) showing lucid dreamers can use specific, pre-arranged patterns of eye movements (e.g., right-left-right-left) to signal in real-time that they are now lucid and engaging in dream experiments. These signals are clearly identifiable on the EOG and suggest a correspondence between dream-eye movements and real-eye movements (as predicted by the so-called scanning hypothesis ; see Dement & Kleitman 1957; Leclair-Visonneau et al. 2010). Retrospective reports confirm that the dreamer really was lucid and signalled lucidity (Dresler et al. 2012; Stumbrys et al. 2014).

Signal-verified lucid dreams have been used to study muscular activity accompanying body movements in dreams (Erlacher et al. 2003; Dresler et al. 2011), for advanced EEG analysis of brain activity during lucid dreaming (Voss et al. 2009), and imaging studies (Dresler et al. 2011, 2012). Eye signals can also be used to measure the duration of different activities performed in lucid dreams; contrary to the cassette theory, lucid dreams have temporal extension and certain dream actions even seem to take slightly longer than in waking (Erlacher et al. 2014). There have also been attempts to induce lucidity through non-invasive electrical stimulation during sleep (Stumbrys et al. 2013; Voss et al. 2014). The combination of signal-verified lucid dreaming with volitional control over dream content, retrospective report, and objective sleep measures has been proposed to provide controlled conditions for the study of conscious experience in sleep and a new methodology for investigating the relationship between conscious experience and neurophysiological processes (Baird et al.2019).

A third line of evidence (Revonsuo 2006: 77) comes from dream-enactment behavior (Nielsen et al. 2009), most prominently in patients with REM-sleep behavior disorder (RBD; Schenck & Mahowald 1996; Schenck 2005; Leclair-Visonneau et al. 2010). Due to a loss of the muscular atonia that accompanies REM sleep in healthy subjects, these patients show complex, seemingly goal-directed outward behaviors such as running or fighting off an attacker during REM sleep. Retrospective dream reports often match these behaviors, suggesting that patients literally act out their dreams during sleep.

While persuasive, these lines of evidence might not satisfy skeptics about dream experience. They might worry that results from lucid dreaming and dream enactment do not generalize to ordinary, non-lucid dreams; they might also construe alternative explanations that do not require conscious experience in sleep. There are also methodological concerns, for instance about how closely sleep-behaviors actually match dream experience. A key issue is that to support the experiential status of dreams, evidence from sleep polysomnography, signal verified lucid dreams, or sleep behavior requires convergence with retrospective dream reports. This means trusting dream reports is built into any attempt to empirically resolve the question of dream experience – which then invites the familiar skeptical concerns. Again, an anti-skeptical strategy may be to appeal to explanatory considerations. In this view, the convergence of dream reports and objective polysomnographic or behavioral observations is best explained by the assumption that dreams are experiences in sleep, and this assumption is strengthened by further incoming findings. This strategy places dream reports at the center of scientific dream research while avoiding the contentious claim that their trustworthiness, and with it the experiential status of dreams, can be demonstrated conclusively by independent empirical means (Windt 2013, 2015a).

Even where philosophers agree dreams are experiences, they often disagree on how exactly to characterize dreaming relative to wake-state psychological terms. Often, questions about the ontology of dreaming intersect with epistemological issues. Increasingly, they also incorporate empirical findings.

The standard view is that dreams have the same phenomenal character as waking perception in that they seemingly put us in contact with mind-independent objects, yet no such object is actually being perceived. This means dreams count as hallucinations in the philosophical sense (Crane & French 2017; Macpherson 2013). Even if, in a particularly realistic dream, my visual experience was exactly as it would be if I were awake (I could see my bedroom, my hands on the bed sheets, etc.), as long as my eyes were closed during the episode, I would not, literally, be seeing anything.

There is some controversy in the psychological literature about whether dreams should be regarded as hallucinations. Some believe the term hallucination should be reserved for clinical contexts and wake-state pathologies (Aleman & Larøi 2008: 17; but see ffytche 2007; ffytche et al. 2010).

The view that dreams involve hallucinations is implicit in Descartes’ assumption that even when dreaming,

it is certain that I seem to see light, hear a noise, and feel heat; this cannot be false, and this is what in me is properly called perceiving ( sentire ). (Descartes 1641: II.9)

It also lies at the heart of Aristotle’s ( On Dreams ) assumption that dreams result from the movements of the sensory organs that continue even after the original stimulus has ceased. He believed that in the silence of sleep, these residual movements result in vivid sensory imagery that is subjectively indistinguishable from genuine perception (see also Dreisbach 2000; Barbera 2008).

The assumption of phenomenological equivalence between dream and waking experience can also be found in Berkeley’s (1710: I.18) idealist claim that the existence of external bodies is not necessary for the production of vivid, wake-like perceptual experience. Similarly, Russell defended sense-data theory by noting that in dreams,

I have all the experiences that I seem to have; it is only things outside my mind that are not as I believe them to be while I am dreaming. (Russell 1948: 149–150)

Elsewhere, he argued dreams and waking life

must be treated with equal respect; it is only by some reality not merely sensible that dreams can be condemned. (Russell 1914: 69)

Hume was less clear on this matter, proposing that dreams occupy an intermediate position between vivid and largely non-voluntary sensory impressions and ideas, or “the faint images of previous impressions in thinking and reasoning” (Hume 1739: 1.1.1.1). On the one hand, as mere creatures of the mind, Hume wanted to categorize dreams as ideas. On the other hand, he acknowledged that in sleep, “our ideas can approach the vivacity of sensory impressions” (Hume 1739: 1.1.1.1). Dreams do not fit comfortably into Hume’s attempt to draw a dichotomous distinction between impressions, including perception, and ideas, including sensory imagination (Ryle 1949; Waxman 1994; Broughton 2006).

Phenomenologists often focus not so much on the quality of dream imagery as on the overall character of experience, noting that dreams are experienced as reality; as in waking perception, we simply feel present in a world. This also sets dreams apart from waking fantasy and daydreams (Husserl 1904/1905; Uslar 1964; Conrad 1968; Globus 1987: 89.

At its strongest, the hallucination view claims that dreaming and waking experience are identical in both the quality of sensory imagery and their overall, self-in-a-world structure (Revonsuo 2006: 84). This claim is central to the virtual reality metaphor , according to which consciousness itself is dreamlike and waking perception a kind of online hallucination modulated by the senses (Llinás & Ribary 1994; Llinás & Paré 1991; Revonsuo 2006; Metzinger 2003, 2009).

This seems to be empirically supported. Neuroimaging studies (Dang-Vu et al. 2007; Nir & Tononi 2010; Desseilles et al. 2011) show that the predominance of visual and motor imagery as well as strong emotions in dreams is paralleled by high activation of the corresponding brain areas in REM sleep, which may exceed waking; at the same time, the cognitive deficits often thought to characterize dreams such as the loss of self-awareness, the absence of critical thinking, delusional reasoning, and mnemonic deficits fit in well with the comparative deactivation of frontal areas (Hobson et al. 2000). Hobson (1988, Hobson et al. 2000) has argued that the vivid, hallucinatory character of dreaming results from the fact that in REM sleep, the visual and motor areas are activated in the same way as in waking perception, the sole difference being dreams’ dependence on internal signal generation. Horikawa and colleagues (2013) used neuroimaging data from sleep onset to predict the types of objects described in mentation reports, which they took to support the perceptual equivalence between dreaming and waking.

Generally, versions of the hallucination view that suggest dreams replicate all aspects of waking perception are too vague to be informative. Especially for subtle perceptual activities (such as visual search), we might not know enough about dream phenomenology to make any strong claims (Nielsen 2010). Specifying points of similarity leads to a more informative and precise, but likely also more nuanced view. Dreams are heterogeneous, and some might be more perception-like while others resemble imagination (Windt 2015a). There might also be differences between or even within specific types of imagery. For example, visual imagery might be quite different from touch sensations, which tend to be rare in dreams (Hobson 1988). Visual dream imagery might overall resemble waking perception but lack color saturation, background detail and focus (Rechtschaffen & Buchignani, 1992). Classifying dreams as either hallucinatory or imaginative is further complicated by the fact that there is strong overlap in cortical activity associated with both visual imagery and perception (Zeidman & Maguire, 2016). This means even a strong overlap in cortical activity between, say, visual dream imagery and visual perception does not necessarily set dreaming apart from waking imagination.

This is also true for evidence on eye movements in dreams. LaBerge and colleagues (2018) recently showed that eye tracking of objects is smooth in lucid dreaming and perceiving, but not in imagining. Drawing from this evidence, Rosen (forthcoming) suggests many dreams mimic the phenomenology of interacting with a stable world, including eye movements and visual search. Others argue we should not analogize dream imagery to mind-independent, scannable objects and that eye movements might instead be implicated in the generation of dream imagery (Windt 2018).

Another way to make sense of the claim that dreaming has the same phenomenal character as waking perception is to say some kinds of dream imagery are illusory: they involve misperception of an external object as having different properties than it actually has (cf. Smith 2002; Crane & French 2017). The illusion view disagrees with the hallucination view on whether dreams have a contemporaneous external stimulus source.

The illusion view has fallen out of favor but has a long history. The Ancients believed dreams have bodily sources. This idea underlies the practice of using dreams to diagnose illness, as practiced in the shrines at Epidaurus (Galen On Diagnosis in Dreams ; van de Castle 1994). Aristotle ( On Dreams ) thought some dreams are caused by indigestion, and Hobbes adopted this view, claiming different kinds of dreams could be traced to different bodily sensations. For instance, “lying cold breedeth Dreams of Feare, and raiseth the thought and Image of some fearfull object” (Hobbes 1651: 91).

Appeals to the bodily sources of dreaming became especially popular in the 19 th and early 20 th centuries. Many believed specific dream themes such as flying were linked to sleeping position (Macnish 1838; Scherner 1861; Vold 1910/1912; Ellis 1911) and realizing, in sleep, that one’s feet are not touching the ground (Bergson 1914).

There were also attempts to explain the phenomenology of dreaming by appealing to the absence of outward movement. The lack of appropriate feedback and of movement and touch sensations was thought to cause dreams of being unable to move (Bradley 1894) or of trying but failing to do something (Gregory 1918).

Some proponents of the “ Leibreiztheorie ” (or somatic-stimulus theory) of dreaming attempted to go beyond anecdotal observations to conduct controlled experiments. Weygandt (1893) investigated the influence of various factors including breathing, blood circulation, temperature changes, urge to urinate, sleeping position, and visual or auditory stimulation during sleep on dream content (see Schredl 2010 for details). Singer (1924) proposed experiments on stimulus incorporation in dreams can inform claims on the ontology of dreaming: If dreams are sensations, a particular auditory stimulus should increase the frequency of dreams in nearby sleepers as well as the frequency of sound in their dreams, and it should decrease the range of quality and intensity of these dreams, making them overall more similar and predictable.

Newer studies provide evidence for the incorporation of external stimuli in dreams, including light flashes, sounds, sprays of water applied to the skin (Dement & Wolpert 1958), thermal (Baldridge 1966), electrical (Koulack 1969), and verbal stimuli (Berger 1963; Breger et al. 1971; Hoelscher et al., 1981), as well as blood pressure cuff stimulation on the leg (Nielsen et al. 1995; Sauvageau et al. 1998).

Muscular activity also often leaves its mark on dreams. It occurs throughout sleep but is especially frequent in REM sleep, mostly in the form of twitching but occasionally also in the form of larger, seemingly goal-directed movements (Blumberg 2010; Blumberg & Plumeau 2016). The relation between outward and dream movements is complex: in some cases, outward movements might mirror dream movements, while in others, sensory feedback might prompt dream imagery (Windt 2018).

Generally, it seems external and bodily stimuli can be related to varying degrees to dream and sleep onset imagery (Nielsen 2017; Windt 2018; Windt et al. 2016). Some of these cases appear to fit the concept of illusion, as in when the sound of the alarm clock is experienced, in a dream, as a siren, or when blood pressure cuff inflation on the leg leads to dreams of wearing strange shoes (Windt 2018; for these and other examples, see Nielsen et al. 1995). In other cases, such as when blood pressure cuff stimulation on the leg prompts a dream of seeing someone else’s leg being run over, describing this as illusory misperception might be less straightforward.

Saying that dreams can be prompted by external stimuli and that in some cases these are best described as illusions is different from the stronger claim, sometimes advanced by historical proponents of somatic-stimulus theory, that dreams generally are caused by external or bodily stimuli. As an example of the stronger claim, consider Wundt’s proposal that the

ideas which arise in dreams come, at least to a great extent, from sensations, especially from those of the general sense, and are therefore mostly illusions of fancy, probably only seldom pure memory ideas which hence become hallucinations. (Wundt 1896: 179)

This claim is likely too strong. It is also likely that appeals to external or bodily stimuli on their own cannot fully explain dream imagery, including when and how external stimuli are incorporated in dreams. Sensory incorporation in dreams is often hard to predict and indirect; associated imagery seems related not just to stimulus intensity, but also to short- and long term memories. A full explanation of dream content additionally has to take the cognitive and memory sources of dreaming into account (Windt 2018; Nielsen 2017; cf. Silberer 1919).

The most important rival to the hallucination view is that dreams are imaginative experiences (Liao & Gendler 2019; Thomas 2014). This can mean dream imagery involves imaginings rather than percepts (including hallucinations or illusions; McGinn 2004), that dream beliefs are imaginative and not real beliefs (Sosa 2007), or both (Ichikawa 2008, 2009). An important advantage is that by assimilating dreams to commonplace mental states such as waking fantasy and daydreaming, rather than a rare and often pathological occurrence such as hallucinations, it provides a more unified account of mental life (Stone 1984). However, the reasons for adopting the imagination view are diverse, and dreams have been proposed to resemble imaginings and differ from perception along a number of dimensions (e.g. McGinn 2004, 2005a,b; Thomas 2014). This issue is complicated by the fact that there is little agreement on the definition of imagination and its relation to perception (Kind 2013).

One way is to deny dreams involve presence or the feeling of being in a world, which many believe is central to waking perception. Imagination theorists compare the sense in which we feel present in our dreams to cognitive absorption, as when we are lost in a novel, film, or vivid daydream (Sartre 1940; McGinn 2004; but see Hering 1947; Globus 1987). Some argue that reflexive consciousness or meta-awareness (as in lucid dreams) interrupts cognitive absorption and terminates the ongoing dream (Sartre 1940), essentially denying lucid dreams are possible.

Another issue is whether dreams are subject to the will (Ichikawa 2009). Imagination is often characterized as active and under our control (Wittgenstein 1967: 621, 633), involving “a special effort of the mind” (Descartes 1641: VI, 2), whereas perception is passive. Because dreams just seem to happen to us without being under voluntary control, they present an important challenge for the imagination view. Ichikawa (2009) argues lucid control dreams show dreams are generally subject to the will even where they are not under deliberate control.

Dreams are widely described as more indeterminate than waking perception (James 1890: 47; Stone 1984). In scientific dream research, vagueness is regarded as one of three main subtypes of bizarreness (Hobson 1988; Revonsuo & Salmivalli 1995). An example are dream characters who are identified not by their behavior or looks, but by just knowing (Kahn et al. 2000, 2002; Revonsuo & Tarkko 2002). Dreams are also attention-dependent and lack foreground-background structure (Thompson 2014); while it is tempting to construe the dream world as rich in detail, there is no more to dreams than meets the eye, and many think dream experience is exhausted by what is the focus of selective attention (Hunter 1983; Thompson 2014).

Indeterminacy is also related to the question of whether we dream in color or in black and white. Based on a review of historical and recent studies, Schwitzgebel (2002, 2011) argues there has been a shift in theories on dream color that coincides with the rise first of black-and-white and then color television. He argues it is unlikely that dreams themselves changed from colored to black and white and back to colored, proposing that a change in opinion is a more plausible explanation. Maybe dreams were either black and white or colored all along; or maybe they are indeterminate with respect to color, as may be the case for imagined or fictional objects; were this the case, it would strengthen the imagination view (Ichikawa 2009). Schwitzgebel’s main point is that reports of colored dreaming are unreliable and our opinions about dreams can be mistaken (but see Windt 2013, 2015a). This relates to Schwitzgebel’s (2011; Hurlburt & Schwitzgebel 2007) general skepticism about the reliability of introspection.

The issue of dream color has led to a number of follow-up studies (Schwitzgebel 2003; Schwitzgebel et al. 2006; Murzyn 2008; Schredl et al. 2008; Hoss 2010). They suggest most people dream in color and a small percentage describe grayscale or even mixed dreams (Murzyn 2008) or dreams involving moderate color saturation (Rechtschaffen and Buchignani 1992). Indeterminacy is rarely reported.

The imagination view has consequences for Cartesian dream skepticism. If dream pain does not feel like real pain, there is a fail-safe way to determine whether one is now dreaming: one need only pinch oneself (Nelson 1966; Stone 1984; but see Hodges & Carter 1969; Kantor 1970). As Locke put it,

if our dreamer pleases to try, whether the glowing heat of a glass furnace, be barely a wandering imagination in a drowsy man’s fancy, by putting his hand into it, he may perhaps be wakened into a certainty greater than he could wish, that it is something more than bare imagination. (Locke 1689: IV.XI.8)

If dreaming feels different from waking, this raises the question why we tend to describe dreams in the same terms as waking perception. Maybe this is because most people haven’t thought about these matters and they would find the imagination view plausible if they considered it (Ichikawa 2009). Or maybe

it is just because we all know that dreams are throughout un like waking experiences that we can safely use ordinary expressions in the narration of them. (Austin 1962: 42)

Some authors classify dreams as imaginings while acknowledging they feel like perceiving. For example, Hobbes describes dreams as “the imaginations of them that sleep” (Hobbes 1651: 90), and imagination as a “ decaying sense ” (Hobbes 1651: 88). Yet he also uses the concepts of imagination and fancy to describe perception and argues “their appearance to us is Fancy, the same waking, that dreaming” (Hobbes 1651: 86).

In the scientific literature, the imagination view is complemented by cognitive theories. Foulkes (1978: 5) describes dreaming as a form of thinking with its own grammar and syntax, but allows that dream imagery is sufficently perception-like to deceive us. Domhoff’s neurocognitive model of dreaming (2001, 2003) emphasizes the dependence of dreaming on visuospatial skills and on a network including the association areas of the forebrain. The theory draws from findings on the partial or global cessation of dreaming following brain lesions (cf. Solms 1997, 2000), evidence that dreaming develops gradually and in tandem with visuospatial skills in children (Foulkes 1993a, 1999; but see Resnick et al. 1994), and results from dream content analysis supporting the continuity of dreaming with waking concerns and memories (the so-called continuity hypothesis ; see Domhoff 2001, 2003; Schredl & Hofmann 2003; Schredl 2006; see also Nir & Tononi 2010).

A number of researchers have begun to consider dreaming in the context of theories of mind wandering. Mind wandering is frequent in waking and involves spontaneous thoughts that unfold dynamically and are only weakly constrained by ongoing tasks and environmental demands (Schooler et al. 2011; Smallwood & Schooler 2015; Christoff et al. 2016). Based on phenomenological and neurophysiological similarities, dreams have been proposed to be an intensified form of waking mind wandering (Pace-Schott 2007, 2013; Domhoff 2011; Wamsley 2013; Fox et al. 2013). This basic idea seems to have been anticipated by Leibniz, who noted that the spontaneous formation of visions in dreams surpasses the capacity of our waking imagination (Leibniz, Philosophical Papers and Letters , Vol. I, 177–178).

The analogy between dreams and waking mind wandering has been discussed in the context of cognitive agency. Metzinger (2013a,b, 2015) describes dreams and waking mind wandering as involving a cyclically recurring loss of mental autonomy, or the ability to deliberately control one’s conscious thought processes. Dreams and waking mind wandering are not mental actions but unintentional mental behaviors, comparable to subpersonal processes such as breathing or heartbeat. Because dreaming and waking mind wandering make up a the majority of our conscious mental lives, he argues that cognitive agency and mental autonomy are the exception, not the rule.

This raises the question of how to make sense of lucid control dreams, which involve both meta-awareness and agency. Windt and Voss (2018) argue that in such cases, spontaneous processes including imagery formation co-exist alongside more deliberate, top-down control; they also argue metacognitive insight and control themselves can have spontaneous elements. This suggests spontaneity and control are not opposites, but a more complex account is needed. Possibly, certain dreams and instances of waking mind wandering can be both spontaneous and agentive.

The analogy with mind wandering might help move forward the debate on the ontology of dreaming. In this debate, a common assumption is that dreams can be categorized as either hallucinatory or imaginative. Yet the application of these terms to dreams quickly runs into counterexamples and it is unclear they are mutually exclusive. One option is pluralism (Rosen 2018b), in which some aspects of dreaming are hallucinatory, others imaginative, and yet again others illusory. Another is that dreams are sui generis, combining aspects associated with wake states such as hallucinating, imagining, or perceiving in a novel manner without mimicking them completely. Windt (2015a) proposes that mind wandering, which describes a range of mental states loosely characterized by their spontaneous and dynamic character, might be particularly suitable for the characterization of dreaming precisely because that term leaves open more specific questions on the phenomenology of dreaming, allowing for variation in control, determinacy, and so on. This might be a good starting point for describing what is unique about dreaming while also acknowledging continuities across sleep-wake states and capitalizing on the strengths of the hallucination, illusion, imagination, and cognitive views.

The second strand of the imagination view argues that dream beliefs are not real beliefs, but propositional imaginings. This may or may not be combined with the claim that dream imagery is imaginative rather than perceptual (Sosa 2007; Ichikawa 2009).

Denying that dream beliefs have the status of real beliefs only makes sense before the background of a specific account of what beliefs are and how they are distinguished from other mental states such as delusions or propositional imaginings. For instance, Ichikawa (2009) argues that if we follow interpretationist or dispositionalist accounts of belief, dream beliefs fall short of real beliefs. He claims dream beliefs lack connection with perceptual experience and fail to motivate actions; consequently, they do not have the same functional role as real beliefs. Moreover, we cannot ascribe dream beliefs to a person by observing them lying asleep in bed. Dream beliefs are often inconsistent with longstanding waking beliefs and acquired and discarded without any process of belief revision (Ichikawa 2009).

This analysis of dream beliefs has consequences for skepticism. If dream beliefs are propositional imaginings, then we do not falsely believe while dreaming that we are now awake, but only imagine that we do (Sosa 2007). It is not clear though that this protects us from deception. If dream beliefs fall short of real beliefs, this might even make the specter of dream deception more worrisome: in mistaking dream beliefs for the real thing, we would now be deceived about the status of our own mental states (Ichikawa 2008).

It is also not clear whether the same type of argument extends to mental states other than beliefs. As Lewis points out, a person might

in fact believe or realize in the course of a dream that he was dreaming, and even if we said that, in such case, he only dreamt that he was dreaming, this still leaves it possible for someone who is asleep to entertain at the time the thought that he is asleep. (Lewis 1969: 133)

Mental states other than believing such as entertaining, thinking, or minimally appraisive instances of taking for granted might be sufficient for deception (Reed 1979).

The debate about dream beliefs is paralleled by a debate about whether delusions are beliefs or imaginings (see Currie 2000; Currie & Ravenscroft 2002; McGinn 2004; Bayne & Pacherie 2005; Bortolotti 2009; Gendler 2013). Both debates might plausibly inform each other, especially as dreams are sometimes proposed to be delusional (Hobson 1999).

3. Dreaming and theories of consciousness

Dreams are a global state of consciousness in which experience arises under altered behavioral and neurophysiological conditions as compared to standard wakefulness; unlike other altered states of consciousness (such as drug-induced or deep meditative states) and pathological wake states (such as psychosis or neurological syndromes), dreams occur spontaneously and regularly in healthy subjects. For both reasons, many regard dreams as a test case for theories of consciousness or even an ideal model system for consciousness research (Churchland 1988; Revonsuo 2006).

Existing proposals differ on the phenomenology of dreaming: referring to dream bizarreness, Churchland describes dream experience as robustly different from waking, whereas Revonsuo argues dreaming is similar to waking and the purest form of experience:

the dreaming brain brings out the phenomenal level of organization in a clear and distinct form. Dreaming is phenomenality pure and simple, untouched by external physical stimulation or behavioural activity. (Revonsuo 2006: 75)

Revonsuo argues dreaming reveals the basic, state-independent structure of consciousness to be immersive: “dreaming depicts consciousness first and foremost as a subjective world- for-me ” (Revonsuo 2006: 75). This leads him to introduce the “world-simulation metaphor of consciousness”, according to which consciousness itself is essentially simulational and dreamlike. This is taken to support internalism about conscious experience.

This latter claim is also contentious. Noë (2004: 213) argues that phenomenological differences between dreaming and waking (such as greater instability of visual dream imagery) result from the lack of dynamic interaction with the environment in dreams. He proposes this shows that neural states are sufficient for dreaming but denies they are also sufficient for perceptual experience.

A possible problem for both views is their reliance on background assumptions about the phenomenology of dreaming and its disconnection from environmental stimuli and bodily sensations. Windt (2015a, 2018) argues both internalism and externalism mistakenly assume dreams to be isolated from external sensory input and own-body perception; she believes both the phenomenology of dreaming and its correlation with external stimuli are complex and variable. She argues the analysis of dreaming does not clearly support either side in the debate on internalism vs externalism (but see Rosen 2018a). Generally, in the absence of a well worked out theory of dreaming and its sleep-stage and neural correlates, proposals for using dreaming as a model system or test case run the risk of relying on an oversimplified description of the target phenomenon (Windt & Noreika 2011).

Recent accounts appealing to generative models and predictive processing (Clark 2013b; Hohwy 2013) suggest a new, unified account of perception, imagination, and dreaming. In these accounts, different mental states, including perception and action, embody different strategies of hypothesis testing and prediction error minimization. Perception is the attempt to model the hidden external causes of sensory stimuli; action involves keeping the internal model stable while changing the sensory input. Clark argues that on such a model,

systems that know how to perceive an object as a cat are thus systems that, ipso facto , are able to use a top-down cascade to bring about the kinds of activity pattern that would be characteristic of the presence of a cat. […] Perceivers like us, if this is correct, are inevitably potential dreamers and imaginers too. Moreover, they are beings who, in dreaming and imagining, are deploying many of the very same strategies and resources used in ordinary perception. (Clark 2013a: 764)

Predictive processing accounts have also been used to explain specific features of dreaming. Bizarreness has been associated with the comparative lack of external stimulus processing, implying dream imagery is relatively unconstrained by prediction errors (cf. Hobson & Friston 2012; Fletcher & Frith 2008; Bucci & Grasso 2017). Windt (2018) suggests a predictive processing account of dream imagery generation that links bodily self-experience to own-body perception and subtle motor behaviors such as twitching in REM sleep (Blumberg 2010; Blumberg & Plumeau 2016). She argues that movement sensations in dreams, in relation to REM-sleep related muscle twitching, involve a form of bodily self-sampling in which coordinated muscular activity contributes to the generation and maintenance of a body model. This is important because in predictive processing accounts neither the bodily nor the external causes of sensory inputs are known; at the same time, having an accurate body model is a prerequisite for action, requiring the system to disambiguate between self- and other generated changes to sensory inputs. Especially in early development, sleep might provide the ideal conditions for exploring one’s own body via subtle but coordinated muscular activity while processing of visual and auditory stimuli is reduced.

Dreams have also been suggested as a test case for whether phenomenal consciousness can be divorced from cognitive access (e.g., Block 2007; but see Cohen & Dennett 2011). Sebastián (2014a) argues that dreams provide empirical evidence that conscious experience can occur independently of cognitive access. This is because during (non-lucid) REM-sleep dreams, the dorsolateral prefrontal cortex (dlPFC) as the most plausible mechanism underlying cognitive access is selectively deactivated (see also Pantani et al. 2018). This would challenge theories linking conscious experience to access, such as higher-order-thought theory (Sebastián 2014b). However, both the hypoactivation of the dlPCF in REM sleep and its association with cognitive access have been debated. Fazekas and Nemeth (2018) suggest that certain kinds of cognitive access may be independent of dlPFC activation, necessitating a more complex account.

Dreaming has been suggested as a model system not just of waking consciousness in general, but also of psychotic wake states in particular. The analogy between dreaming and madness has a long philosophical history (Plato, Phaedrus ; Kant 1766; Schopenhauer 1847) and finds particularly stark expression in Hobson’s claim that “dreaming is not a model of a psychosis. It is a psychosis. It’s just a healthy one” (Hobson 1999: 44). Gottesmann (2006) proposes dreaming as a neurophysiological model of schizophrenia. There is a rich discussion on the theoretical and methodological implications of dream research for psychiatry (see Scarone et al. 2007; d’Agostino et al. 2013; see Windt & Noreika 2011 as well as the other papers in this special issue) and a number of studies have investigated differences in dream reports from schizophrenic and healthy subjects (Limosani et al. 2011a,b).

Rather than likening dreaming to waking in general or specific wake states such as psychosis, there have also been attempts to compare specific dream phenomena to wake-state delusions. Gerrans (2012, 2013, 2014) focuses on character misidentification in dreams and delusions of hyperfamiliarity (such as the Frégoli delusion, in which strangers are mistakenly identified as family members, and déjà vu ) to argue that anomalous experience and faulty reality testing both play a role in delusion formation. Rosen (2015) analyzes instances of thought insertion and of auditory hallucinations, which are key symptoms of schizophrenia, to raise broader questions about the altered sense of agency in dreams as compared to waking.

Philosophers have focused almost exclusively on dreaming, largely leaving to the side questions about dreamless sleep including whether it is uniformly unconscious. In recent years there has been a surge of interest in the possibility of dreamless sleep experience and foundational issues about the definition of sleep and waking. This has been paralleled by growing interest in dreaming in NREM sleep.

Conceptually, interest in dreamless sleep experience has been facilitated by the precise definition of dreaming offered by simulation views (Revonsuo et al. 2015). If dreams are immersive sleep experiences characterized by their here -and- now structure, it makes sense to ask whether this is true for all or just a subset of sleep-related experiences and whether non-immersive sleep experiences exist. By contrast, if dreaming is broadly identified with any conscious mentation in sleep (Pagel et al. 2001), there is no conceptual space for dreamless sleep experience.

Following Thompson's (2014, 2015) discussion of dreamless sleep in Indian and Buddhist philosophy, Windt and colleagues (2016; see also Windt 2015b) introduce a framework for different kinds of dreamless sleep experience ranging from thinking and isolated imagery, perception, or bodily sensations, where these lack integration into a scene, to minimal kinds of experience lacking imagery or specific thought contents. A possible example of minimal phenomenal experience in sleep are white dreams, where people report having had experiences during sleep but cannot remember any details. Taken at face value, some white dream reports might describe experiences that lack reportable content (Windt 2015b); others might describe forgotten dreams or dreams with degraded content (Fazekas et al. 2018). Another example are reports of witnessing dreamless sleep, as described in certain meditation practices. This state is said to involve non-conceptual awareness of sleep, again in the absence of imagery or specific thought contents, and loss of sense of self (Thompson 2014, 2015). Some schools in Buddhist philosophy explain claims of deep and dreamless sleep by saying we never fully lose consciousness in sleep (Prasad 2000, 66; and Thompson 2014, 2015).

Empirically, interest in dreamless sleep experience is paralleled by increasing interest in experiences in NREM sleep (Fazekas et al. 2018). Most researchers now accept that dreaming is not confined to REM sleep, but also occurs at sleep onset and in NREM sleep. The deeper stages of NREM sleep are particularly interesting as they involve roughly similar proportions of dreaming, unconscious sleep, and white dreams (Noreika et al. 2009: Siclari et al. 2013, 2017). In the search for the neural correlates of dreaming vs unconscious dreamless sleep, this makes comparisons within the same sleep stage possible and avoids confounds involved in comparing presumably dreamful REM sleep with presumably dreamless NREM sleep. Findings suggest that activity in the same parietal hot zone underlies dreaming in both NREM and REM sleep (Siclari et al. 2017).

Where sleep and dream research have traditionally tried to identify the sleep stage correlates of dreaming, newer research suggests local changes occurring independently of sleep stages might in fact be more relevant. Traditionally regarded as global, whole-brain phenomena, there is now increasing evidence that sleep itself is locally driven, and local changes in sleep depth might be associated with changes in sleep-related experience (Siclari & Tononi 2017; Andrillon et al. 2019). While sleep and dream research are often considered as separate fields, changes in how sleep in general and sleep stages in particular are defined appear closely associated with changes in the theoretical conception of dreaming and its empirical investigation.

Historically, discoveries about dreaming have precipitated changing conceptions of sleep (for an excellent history of the study of sleep and dreaming, see Kroker 2007). Following Aristotle ( On Sleeping and Waking ), sleep was traditionally defined in negative terms as the absence of wakefulness and perception. This is still reflected in Malcolm’s assumption that “to a person who is sound asleep, ‘dead to the world’, things cannot even seem” (Malcolm 1956: 26). With the discovery of REM sleep, sleep came to be regarded as a heterogeneous phenomenon characterized by the cyclic alteration of different sleep stages. REM sleep was now considered as “neither sleeping nor waking. It was obviously a third state of the brain, as different from sleep as sleep is from wakefulness” (Jouvet 1999: 5). The folk-psychological dichotomy between sleep and wakefulness now seemed oversimplified and empirically implausible. At the same time dreaming, which had previously been considered as an intermediate state of half-sleeping and half-waking, came to be regarded as a genuine sleep phenomenon, but narrowed to REM sleep. Today, the framework for describing dreams and other sleep-related experiences is more precise, but dreaming has also been cast adrift from REM sleep.

A closely associated issue is how to define waking. Crowther’s (2018) capacitation thesis casts waking consciousness as a state in which the individual is fully switched on to their environment, but also to their own epistemic (cf. O’Shaugnessy 2002) and agentive potential; the waking individual is empowered to act and think in certain ways, though this potential need not be actualized. By contrast, dreaming is an “imagining-of consciousness” (O’Shaughnessy 2002: 430) and consciousness is conceptually tied to wakefulness. Because in lucid dreams, the epistemic and agentive profile of waking is at least partly realized, they might, according to Crowther, be regarded as closer to waking than nonlucid dreams.

This account of waking and sleep may also have consequences for the imagination model of dreaming and dream skepticism (Soteriou 2017). As in the imagination model, dreaming would be passive and action, including cognitive agency, would be tied to waking. If dreaming nonetheless involved passive episodes of imagining oneself to be active, one would be unable to tell that one were dreaming and imagining, as this insight would require the exercise of real agency. The sceptical consequence would be that when dreaming, one would lose agency as well as the capacity to gain insight into one’s current state. Yet our ability to know we are waking when waking would be unscathed; according to Soteriou, waking would thus have an epistemic function connected to the capacity to exercise agency over our mental lives.

Finally, definitions of consciousness themselves are bound up with conceptions of sleep and dreaming. As dreaming went from a state whose experiential status was doubted to being widely recognized as a second global state of consciousness, consciousness sometimes came to be defined contrastively as that which disappears in deep, dreamless sleep and reappears in waking and dreaming (Searle 2000; Tononi 2008). In light of dreamless sleep experience, such definitions are problematic (Thompson 2014, 2015; Windt 2015b; Windt et al. 2016). Dreamless sleep experience has been proposed to be particularly relevant for understanding minimal phenomenal experience, or the conditions under which the simplest kind of conscious experience arises (Windt 2015b). The investigation of dreamless sleep might thus shed light on the transition from unconscious sleep to sleep-related experience.

We almost always have a self in dreams, though this self can sometimes be a slightly different (e.g. older or younger) version of our waking self or even a different person entirely. Dreams therefore raise interesting questions about the identity between the dream and waking self. Locke (1689) invites us to imagine two men alternating in turns between sleep and wakefulness and sharing one continuously thinking soul (Locke 1689: II.I.12). He argues that if one man retained no memory of the soul’s thoughts and perceptions while it was linked to the other man’s body, they would be distinct persons. His position is that personal identity depends on psychological continuity, including recall: in the absence of recall, as illustrated by the toy example of two people sharing one soul, continuous conscious thinking does not suffice for identity. Locke also rejects the possibility of unrecalled dreams and the idea that we dream throughout sleep, remembering only a small proportion of our dreams (Locke 1689: II.I.19).

Valberg distinguishes between the subject of the dream (i.e., the dream self) and the sleeping person who is the dreamer of the dream and recalls it upon awakening (Valberg 2007). He argues that awakening from a dream involves crossing a chasm between discrete worlds with discrete spaces and times; it does not make sense to say that “the ‘I’ at these times [is] a single individual who crosses from one world to the other” (Valberg 2007: 69). According to Valberg, this is relevant to dream skepticism because there is no simple way to make sense of the claims that it is I who emerge from a dream or that I was the victim of dream deception.

Vicarious dreams, or dreams in which the protagonist of the dream seems to be a different person from the dreamer, are particularly puzzling with respect to identity. They may even raise the question of whether the dream self has an independent existence (Rosen & Sutton 2013: 1047). Such dreams are superficially similar to cases in which we imagine being another person, but according to Rosen and Sutton require a different explanation: in the case of dreaming, the imagined person’s thoughts are not framed as diverging from one’s own and one does not retain one’s own perspective in addition to the imagined one; in nonlucid dreams, only the perspective of the dream’s protagonist is retained.

The dream self is also at the center of simulation views of dreaming, which define dreaming via its immersive, here and now character as the experience of a self in a world. This leads to further questions about the phenomenology of self-experience in dreams and how it is different from waking self-experience. Different versions of the simulation view focus on different aspects of self- and world experience in dreams, ranging from social simulation (Revonsuo et al. 2015) to the typical features of selfhood in dreams (Revonsuo 2005, 2006, Metzinger 2003, 2009) to the minimal conditions for experiencing oneself as a self in dreams and what this tells us about minimal phenomenal selfhood in general (Windt 2015a, 2018). Yet these different versions of the simulation view are largely complementary and together have forged unity in a field that was previously hampered by lack of agreement about the definition of dreaming. They also integrate the philosophy of dreaming and scientific dream research.

As so often in debates about dreaming, there is disagreement about basic phenomenological questions. Revonsuo (2005) describes self-experience including bodily experience in dreams as identical to waking, whereas Metzinger (2003, 2009; see also Windt & Metzinger 2007) argues that important layers of waking self-experience (such as autobiographical memory, agency, a stable first-person perspective, metacognitive insight, and self-knowledge) are missing in nonlucid dreams. He argues this is due to the cognitive and mnemonic deficit that characterizes nonlucid dreams (cf. Hobson et al. 2000). Windt (2015a) analyzes the range of cognitive and bodily self-experience in dreams, both of which she describes as variable. She argues that in a majority of cases, dreams are weakly phenomenally embodied states in which bodily experience is largely related to movement sensations but a detailed and integrated body representation is lacking; instead, bodily experience in dreams is largely indeterminate (for an attempt to test this empirically, see Koppehele-Gossel et al. 2016). She proposes this is because dreams are also weakly functionally embodied states, in which the specific pattern of bodily experience reflects altered processing of bodily sensations (as in the illusion view). She also analyzes instances of bodiless dreams, in which dreamers say they experienced themselves as disembodied entities, to argue that self-experience can be reduced to pure spatiotemporal-self-location (Windt 2010); she proposes these cases can help identify the conditions for the emergence of minimal phenomenal selfhood (Blanke & Metzinger 2009; see also Metzinger 2013b).

How the phenomenology of dreaming compares to waking and what to say about how the dream self relates to the waking self bears on questions about the moral status of dreams. For Augustine ( Confessions ) dreams were a cause of moral concern because of their indistinguishability from waking life. What particularly worried him about dreams of sexual acts was their vividness, as well as the feeling of pleasure and seeming acquiescence or consent on the part of the dreamer. He concluded, however, that the transition from sleep to wakefulness involves a radical chasm, enabling the dreamer to awaken with a clear conscience and absolving them from taking responsibility for their dream actions.

What exactly Augustine thought the chasm between dreaming and waking consists in allows for different interpretations (Matthews 1981). Firstly, if the dream and waking self are not identical, then waking Augustine is not morally responsible for dream-Augustine’s actions. Secondly, actions performed in dreams might be morally irrelevant because they did not really happen. And thirdly, assuming that moral responsibility requires the ability to act otherwise, dreams provide no grounds for moral concern because we cannot refrain from having certain types of dreams.

The issue of dream immorality may also present a choice point between different accounts of moral evaluation. Where internalists assume the moral status of a person’s actions is entirely determined by internal factors such as intentions and motives, externalists look beyond these to the effects of actions. Driver (2007) argues that the absurdity of dream immorality itself should count against purely internalist accounts; yet she also acknowledges this absurdity is not a necessary feature of dreams.

Central to the question of dream immorality is the status of dreams as actions rather than mere behaviors. Mullane (1965) argues that while we don’t have full control over our dreams, they are not completely involuntary either; as is the case for blushing, considerable effort is required to attain control over our dreams and in some cases they can even be considered as actions. That lucid dream control is, to some extent, a learnable skill (Stumbrys et al. 2014) lends some support to this claim.

6. The meaning of dreams and the functions of dreaming

Philosophical discussions of dreaming tend to focus on (a) dream deception and (b) questions about the ontology of dreaming, its moral status, etc., that tend to intersect with dream skepticism. By contrast, the main source of interest in dreams outside of philosophy traditionally has been dream interpretation and whether dreams are a source of knowledge and insight. Historically, the epistemic status of dreams and the use of prophetic and diagnostic dreams was not just a theoretical, but a practical problem (Barbera 2008). Different types of dreams were distinguished by their putative epistemic value. Artemidorus, for instance, used the term enhypnion to refer to dreams that merely reflect the sleeper’s current bodily or psychological state and hence do not merit further interpretation, whereas he reserved the term oneiron for meaningful and symbolic dreams of divine origin.

The practice of dream interpretation was famously attacked by Aristotle in On Prophecy in Sleep . He denied that dreams are of divine origin, but allowed that occasionally, small affections of the sensory organs as might stem from distant events that cannot be perceived in waking are perceptible in the quiet of sleep. He also believed such dreams were mostly likely to occur in dullards whose minds resemble an empty desert – an assessment that was not apt to encourage interest in dreams (Kroker 2007: 37). A similarly negative view was held by early modern philosophers who believed dreams were often the source of superstitious beliefs (Hobbes 1651; Kant 1766; Schopenhauer 1847).

In Freudian dream theory, dream interpretation once more assumed a prominent role as the royal road to knowledge of the unconscious. This was associated with claims about the psychic sources of dreaming. Freud (1899) also rejected the influence of external or bodily sources, as championed by contemporary proponents of somatic-stimulus theory.

In the neuroscience of dreaming, Hobson famously argued that dreams are the product of the random, brain-stem driven activation of the brain during sleep (Hobson 1988) and at best enable personal insights in the same way as a Rorschach test (Hobson et al. 2000). Dennett (1991) illustrates the lack of design underlying the production of dream narratives through the “party game of psychoanalysis”, which involves an aimless game of question-and-answer. In the game, players follow simple rules to jointly produce narratives that can seem symbolic and meaningful, even though no intelligent and deliberate process of narration was involved.

Even if we grant that dreams are not messages from a hidden entity in need of decoding, this does not imply that dream interpretation cannot be a personally meaningful source of insight and creativity (Hobson & Wohl 2005). Whether and under which conditions, and following which methods, dream interpretation can lead to personally significant insights is an empirical question that is only beginning to be investigated systematically (see Edwards et al. 2013).

Finally, throughout history, views on the epistemic status of dreams and the type of knowledge to be gained from dream interpretation (e.g., knowledge about the future, diagnosis of physical illness, or insights about one’s current concerns) often changed in tandem with views on the origin and sources of dreaming, which gradually moved from divine origins and external sources, via the body, to the unconscious, and finally to the brain.

Different theories on the functions of dreaming have been proposed and the debate is ongoing. An important distinction is between the functions of sleep stages and the functions of dreaming. Well-documented functions of REM sleep include thermoregulation and the development of cortical structures in birds and mammals, as well as neurotransmitter repletion, the reconstruction and maintenance of little-used brain circuits, the structural development of the brain in early developmental phases, as well as the preparation of a repertoire of reflexive or instinctive behaviors (Hobson 2009). Yet none of these functions are obviously linked to dreaming. An exception is protoconsciousness theory, in which REM sleep plays an important role in foetal development by providing a virtual world model even before the emergence of full-blown consciousness (Hobson 2009: 808) .

Numerous studies have investigated the contribution of sleep to memory consolidation, with different sleep stages promoting different types of memories (Diekelmann et al. 2009; Walker 2009). However, only a few studies have investigated the relationship between dream content and memory consolidation in sleep (for a review, see Nielsen & Stenstrom 2005). Dreams rarely involve episodic replay of waking memories (Fosse et al. 2003). The incorporation of memory sources seems to follow a specific temporal pattern in which recent memories are integrated with older but semantically related memories (Blagrove et al. 2011). Nielsen (2017) presents a model of how external and bodily stimuli on one hand and short- and long-term memories on the other hand form seemingly novel, complex, and dreamlike images at sleep onset; he proposes these microdreams shed light on the formation and sources of more complex dreams. There is also some evidence that dream imagery might be associated with memory consolidation and task performance after sleep, though this is preliminary (Wamsley & Stickgold 2009, 2010; Wamsley et al. 2010).

Prominent theories on the function of dreaming focus on bad dreams and nightmares. It has long been thought that dreaming contributes to emotional processing and that this is particularly obvious in the dreams of nightmare sufferers or in dreams following traumatic experiences (e.g., Hartmann 1998; Nielsen & Lara-Carrasco 2007; Levin & Nielsen 2009; Cartwright 2010; Perogamvros et al. 2013). Based on the high prevalence of negative emotions and threatening dream content, threat simulation theory suggests that the evolutionary function of dreaming lies in the simulation of ancestral threats and the rehearsal of threatening events and avoidance skills in dreams has an adaptive value by enhancing the individual’s chances of survival (see Revonsuo 2000; Valli 2008). A more recent proposal is social simulation theory, in which social imagery in dreams supports social cognition, bonds, and social skills. (Revonsuo et al. 2015).

An evolutionary perspective can also be fruitfully applied to specific aspects of dream phenomenology. According to the vigilance hypothesis , natural selection disfavored the occurrence of those types of sensations during sleep that would compromise vigilance (Symons 1993). Dream sounds, but also smells or pains might distract attention from the potentially dangerous surroundings of the sleeping subject, and the vigilance hypothesis predicts that they only rarely occur in dreams without causing awakening. By contrast, because most mammals sleep with their eyes closed and in an immobile position, vivid visual and movement hallucinations during sleep would not comprise vigilance and thus can occur in dreams without endangering the sleeping subject. Focusing on the stuff dreams are not made of might then be at least as important for understanding the function of dreaming as developing a positive account.

Finally, even if dreaming in general and specific types of dream content in particular were found to be strongly associated with specific cognitive functions, it would still be possible that dreams are mere epiphenomena of brain activity during sleep (Flanagan 1995, 2000). It is also possible that the function of dreams is not knowable (Springett 2019).

A particular problem for any theory on the function of dreaming is to explain why a majority of dreams are forgotten and how dreams can fulfill their putative function independently of recall. Crick and Mitchinson (1983) famously proposed that REM sleep “erases” or deletes surplus information and unnecessary memories, which would suggest that enhanced dream recall is counterproductive. Another problem is that dreaming can be lost selectively and independently of other cognitive deficits (Solms 1997, 2000).

Some of the problems that arise for theories on the functions of dreaming can be avoided if we do not assume that dreaming has a specific function, separate from the function(s) of conscious wakeful states. This depends on the broader taxonomy of dreaming in relation to wakeful states. For example, if dreaming is continuous with waking mind wandering, imagination, and/or own-body perception, we should not expect it to have a unique function, but rather to express a similar function as these wakeful states, perhaps to varying degrees. Nor should we expect dreams to have a single function; the functions of dreaming might be as varied and complex as those of consciousness, and given the complexity of the target phenomenon, the failure to pin down a single function should not be surprising (Windt 2015a).

Questions about dreaming in different areas of philosophy such as epistemology, ontology, philosophy of mind and cognitive science, and ethics are closely intertwined. Scientific evidence from sleep and dream research can meaningfully inform the philosophical discussion and has often done so in the past. The discussion of dreaming has also often functioned as a lens on broader questions about knowledge, morality, consciousness, and self. Long a marginalized area, the philosophy of dreaming and of sleep is central to important philosophical questions and increasingly plays an important role in interdisciplinary consciousness research, for example in the search for the neural correlates of conscious states, in conscious state taxonomies, and in research on the minimal conditions for phenomenal selfhood and conscious experience.

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How to cite this entry . Preview the PDF version of this entry at the Friends of the SEP Society . Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO). Enhanced bibliography for this entry at PhilPapers , with links to its database.

Philosophy of Dreaming , entry in the Internet Encyclopedia of Philosophy .
Dreams , PhilPapers collection.
Dreams and Skepticism , PhilPapers collection.

Acknowledgments

I want to thank Regina Fabry and two anonymous reviewers for helpful comments and constructive criticism on an earlier version of this manuscript. And as always, I am greatly indebted to Stefan Pitz for his support.

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Why Do We Dream?

Dreams are caused by neural processes in sleep but may not have any function..

Posted December 1, 2022 | Reviewed by Michelle Quirk

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Many theorists from Freud to current neuroscientists have tried to explain the function of dreams.
Increased understanding of the brain suggests that dreams are byproducts of neural processes with no special function.
These neural theories of dreams are incomplete without a complementary theory of consciousness.

Dreams are conscious experiences that occur during sleep, and today there are many alternatives to Freud’s theory that dreams are wish fulfillments.

Dreams Are Divine Communications

Many cultures, from the ancient Greeks to Indigenous American groups such as the Iroquois, have assigned spiritual significance to dreams. We dream because the gods are speaking to us or because we can transcend the limitations of our bodies and explore the future. The problem with these views is lack of evidence for gods and their communications. Most dreams are about mundane activities such as work and family and should be open to nonspiritual explanations.

Dreams Are Wish Fulfilments

Sigmund Freud thought that his theory of dreams was his most valuable discovery, important for giving a scientific explanation of why people dream and also for suggesting dream analysis as a useful part of psychotherapy . Dreams are symptoms of unconscious wishes that may be at the root of psychological problems. Freud struggled to explain why most dreams are disagreeable and why many patients do not benefit from his psychoanalytic techniques. Another puzzle for the Freudian approach is why most dreams are not remembered.

Dreams Are Byproducts of Neural Processing

J. Allan Hobson was a Harvard psychiatrist who pioneered the first serious scientific alternative to Freud’s ideas about dreams. He proposed that dreams are brain processes resulting from neural activations that occur during rapid-eye-movement (REM) sleep, without the usual sensory and motor inputs that are blocked by the thalamus. The brain tries to make sense of these activations using its memories, but the results are delusional and of little psychological significance. Many of Hobson’s proposed neural mechanisms turned out to be wrong—for example, through the finding that dreams also occur in non-REM sleep.

G. William Domhoff agrees with Hobson that dreams have no adaptive biological function but offers a different neural explanation. The default network connects important regions in different parts of the brain and operates in the absence of sensory inputs. Domhoff thinks that during sleep the default network generates imaginations and simulations that produce dreams. Domhoff takes seriously the thousands of reports of dreams that have been accumulated in dream banks and sees dreaming as continuous with everyday cognition . However, he does not have a theory of consciousness that could explain why the activity of the default network generates experiences such as visual imaginings and feelings of anxiety .

Dreams Are Emotional Regulation

Not all neuroscientists think that dreams are useless. Matthew Walker describes many valuable biological functions of sleep, including restoring the brain, metabolism, immune system, and cardiovascular system. He also thinks that the neural processes of dreaming bring important benefits for regulating the emotions and creativity . Sleep is known to be important for consolidating daytime memories into permanent storage, and emotion -related areas of the brain are also active during this process. Walker thinks that REM sleep helps us not only to remember emotionally important events but also to dissolve painful emotional charges. Moreover, the unusual associations that occur in dreaming can help to generate creative new ideas. However, Walker does not show that emotional regulation and creativity are the reasons that organisms evolved brains that dream. Perhaps emotion regulation and creativity are just useful side effects of dreaming, not its biological purpose.

Dreams Are Cognitive Explorations

An alternative function of dreams is proposed by neuroscientists Antonio Zadra and Robert Stickgold. They propose a model of dream function called NEXTUP for “network exploration to understand possibilities.” Dreaming serves to extract new knowledge from existing memories by discovering and strengthening existing associations. When we dream about being chased, having sex , or school examinations, we are preparing ourselves to deal with a changing world. But whether dreams are useful in this way is debatable given that most of them are never remembered, many of them are bizarrely unrealistic, and the majority of dreams are unpleasant.

Dreams Are Predictive Processing

In his later years, J. Allan Hobson tied his activation-synthesis view of dreaming to the increasingly popular view that the brain functions primarily as a prediction engine operating by Bayesian inference. In a previous post , I argued that the brain has many important functions besides prediction and that there is no reason to think that it uses probabilistic calculations to carry out these functions. Like the NEXTUP model, Hobson came to see dreams not as random but as having useful benefits in making predictions, which is problematic given the bizarre and forgettable character of most dreams. Many people dream of flying and falling, two activities that most of us do rarely.

What Causes Dreams?

Dreams result from unusual patterns of neural firing that occur during sleep. In order to restore the body and brain, sleep shuts down the body’s sensory inputs and motor activities that normally constrain neural firings. Aberrant neural signals may also result as side effects of memory consolidation and the replenishment of neurotransmitters that were depleted during the brain’s daily activities.

The brain is not just a prediction engine but also a coherence engine that tries to make sense of what is going on, internally and externally. For example, the brain stem interacts with sensory inputs and other brain areas to produce physical balance that enables us to remain upright while moving around the world. Sometimes, however, balance goes wrong when defective signals from the inner ear or eyes or brain damage generate misinterpretations that lead to vertigo, nausea, or falls. Similarly, during dreaming the brain generates false interpretations that we are having perceptions, emotions, and thoughts about reality .

I, therefore, suspect that dreams result from aberrant signals and more-or-less coherent interpretations that depend on many brain areas, not just the default network. Most interpretations carried out by patterns of neural firing are unconscious, but some of them emerge into conscious experiences that are remembered after waking. Dreams are side effects of neural mechanisms for sleep and consciousness, and no special significance should be attributed to them.

Domhoff, G. W. (2018). The emergence of dreaming: Mind-wandering, embodied simulation, and the default network . Oxford: Oxford University Press.

Domhoff, G. W. (2022). The neurocognitive theory of dreaming: The where, how, when, what, and why of wreams . Cambridge, MA: MIT Press.

Freud, S. (1938). The interpretation of dreams (A. A. Brill, Trans.). New York, Modern Library.

Hobson, J. A. (1988). The dreaming brain. New York: Basic Books.

Hobson, J. A., Hong, C. C.-H., & Friston, K. J. (2014). Virtual reality and consciousness inference in dreaming. Frontiers in Psychology , 5, 1133.

Thagard, P. (2022). Balance: How it works and what it mean s. New York: Columbia University Press.

Walker, M. (2017). Why we sleep: Unlocking the power of sleep and dreams. New York: Simon and Schuster.

Zadra, A., & Stickgold, R. (2022). When brains dream: Understanding the science and mystery of our dreaming minds . New York: W. W. Norton.

Paul Thagard, Ph.D. , is a Canadian philosopher and cognitive scientist. His latest book, published by Columbia University Press, is Falsehoods Fly: Why Misinformation Spreads and How to Stop It.

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December 12, 2023

Why Do We Dream? Maybe to Ensure We Can Literally ‘See’ the World upon Awakening

A theory holds that dreams are a way for the visual cortex of the brain to “defend its turf” against being “taken over” to process inputs from other senses

By Roberta McLain

Artist's 3-d rendering highlighting the eye and pathway to the visual cortex in the brain

Visual pathway and cortex.

janulla/Getty Images

Dreams have fascinated people for millennia, yet we struggle to understand their purpose. Some theories suggest dreams help us deal with emotions, solve problems or manage hidden desires. Others postulate that they clean up brain waste, make memories stronger or deduce the meaning of random brain activity. A more recent theory suggests nighttime dreams protect visual areas of the brain from being co-opted during sleep by other sensory functions, such as hearing or touch.

David Eagleman, a neuroscientist at Stanford University, has proposed the idea that dreaming is necessary to safeguard the visual cortex—the part of the brain responsible for processing vision. Eagleman’s theory takes into account that the human brain is highly adaptive, with certain areas able to take on new tasks, an ability called neuroplasticity. He argues that neurons compete for survival. The brain, Eagleman explains, distributes its resources by “implementing a do-or-die competition” for brain territory in which sensory areas “gain or lose neural territory when inputs slow, stop or shift.” Experiences over a lifetime reshape the map of the brain. “Just like neighboring nations, neurons stake out their territory and chronically defend them,” he says.

Eagleman points to children who have had half their brain removed because of severe health problems and then regain normal function. The remaining brain reorganizes itself and takes over the roles of the missing sections. Similarly, people who lose sight or hearing show heightened sensitivity in the remaining senses because the region of the brain normally used by the lost sense is taken over by other senses.

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Reorganization can happen fast. Studies published in 2007 and 2008 by Lotfi Merabet of Harvard Medical School and his colleagues showed just how quickly this takeover can happen. The 2008 study, in which subjects were blindfolded, revealed that the seizing of an idle area by other senses begins in as little as 90 minutes. And other studies found that this can occur within 45 minutes.

When we sleep, we can smell, hear and feel, but visual information is absent—except during REM sleep. About 90 minutes after drifting off to sleep, you enter REM. It begins when neurons in your brain stem, the stalklike section at the bottom of the organ, signal the beginning of two important tasks. Activity of these neurons, for one, paralyze major muscles, preventing the sleeper from acting out what is happening in the dream. Also, these brain cells send messages directly to the visual cortex, which initiates the dreaming process.

Why does REM follow that timetable? It conforms to when the visual cortex needs to start defending its territory, Eagleman argues. Scans of dreaming people show most of the brain activity associated with REM is within the visual cortex. Dreams are the brain’s way of fighting takeover from other senses, according to Eagleman, and REM activation prompts internally generated activity in the visual cortex as a means to safeguard its territory. As long as the neurons in the visual cortex are actively performing their customary job—in this case, generating visual imagery—they will not be commandeered by nearby neurons that process other sensory information.

Eagleman argues that the more plastic the brain, the more REM sleep is necessary to mount a defense. For babies to develop properly, they must sleep a lot, spending almost 50 percent of their time in REM sleep. But as people age, their brain becomes less flexible. (Think of how easily children learn languages, compared with adults.) At the same time, adults spend less time in REM sleep.

The correlation between adaptability and REM seems to hold across species. According to Eagleman, “Mother Nature drops human brains into the world half-baked and lets experience take over and shape them.” He argues the less hardwired a species’ brain is at birth, the more ability it has to adapt and learn from experience. But this has its disadvantages. For example, fawns and calves are able to walk within hours of birth because the behavior is hardwired. Human babies, with their more adaptable brains, require significantly more REM sleep than animals born with more hardwired brains.

Some researchers—in particular, dream researchers—disagree with Eagleman’s hypothesis. One example that raises doubts is the fact that the blind mole rat does not see and still experiences REM sleep. Yet some evolutionary adaptations are vestigial remnants of traits that were useful in the past but have become less significant as animals have evolved. So perhaps there was no pressure for blind mole rats to lose REM activity as they evolved without vision.

Antonio Zadra, a dream researcher at the University of Montreal, claims Eagleman’s theory “has little to do with actual dreaming and explains almost nothing about dreams per se, as opposed to REM sleep.” He asserts the theory “is, for me and many others who actually work in the field, silly and overly reductionistic and simplistic.”

Deirdre Leigh Barrett, a psychologist at Harvard University, former president of the International Association for the Study of Dreams and author of The Committee of Sleep , however, is more willing to consider Eagleman’s hypothesis. “It’s very convincing that there's a correlation between smarter animals and more elaborate brains,” she says. As far as dreams defending brain real estate, “I have a little more trouble with the visual argument, but it’s interesting.”

Eagleman says that his theory can accommodate other explanations for dreams and that REM sleep may serve many purposes besides protecting the visual cortex. Think of dreaming like a computer screen saver that is set to go off every 90 minutes—except that instead of protecting against frozen images, dreams prevent the visual cortex from being usurped by other functions. These visual hallucinations in the night may let us see during the day.

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10 theories that explain why we dream

The study of dreaming is called oneirology, and it's a field of inquiry that spans neuroscience, psychology, and even literature. Still, the plain fact is that the reasons why we dream are still mysterious. But that hasn't stopped scientists from coming up with some pretty fascinating hypotheses. Here are ten of them.

1. Wish fulfillment

One of the first sustained efforts to study dreams scientifically was spearheaded by the psychoanalyst Sigmund Freud, in the early twentieth century . After analyzing the dreams of hundreds of his patients, he came up with a theory that still resonates with a lot of researchers today: dreams are wish-fulfillments. Any dream, no matter how terrifying, can be looked at as a way of getting something that you want, either literally or symbolically. For example, say you have a terrifying and sad dream about your mother dying. Why would that be a wish-fulfillment? Maybe, Freud would say, you are having a conflict with your mother that would be easily resolved if she were out of the picture. So you don't want your mother to die, but you do want to deal with that conflict. By thinking of dreams in this light, Freud was able to help many of his patients unbury hidden emotions that they hadn't dealt with.

2. An accidental side-effect of random neural impulses

If you buy into Freud's idea about dreams, their subject matter is deeply meaningful. They can reveal wishes or emotions you didn't realize you had. But another popular school of thought holds that dreams are actually just a kind of brain fart, an accidental side-effect of activated circuits in the brain stem and stimulation of the limbic system that's involved with emotions, sensations and memories. J. Allan Hobson, the psychiatrist who popularized this idea, calls it the "activation-synthesis theory." In a nutshell, the brain tries to interpret these random signals, resulting in dreams.

What's particularly interesting about this theory is that it could also help to explain why humans use storytelling as a way to make sense of an often random, chaotic universe. If dreams are the meanings our brains supply to random neural firing in our limbic system, then stories are like waking dreams, meanings we use to paper over the fundamentally disorganized signals we receive from the world around us.

3. Encoding short-term memories into long-term storage

Maybe dreams are just randomly-generated stories caused by neural impulses, but perhaps there's also a reason for them, too. To explore this idea, psychiatrist Jie Zhang, proposed the continual-activation theory of dreaming, which refers to the idea that our brains are always storing memories regardless of whether we're awake or asleep. But dreams are a kind of "temporary storage" area of consciousness, a spot where we hold memories before we move them from short-term to long-term storage. They flash through our minds as dreams before we secret them away in the files of our memory.

4. Garbage collection

Dubbed the "reverse learning" theory , this idea suggests that we dream to get rid of undesirable connections and associations that build up in our brains throughout the day. Basically, dreams are garbage collection mechanisms, clearing our minds of useless thoughts and making way for better ones. Essentially, we dream in order to forget. Dreams help us eliminate the information overload of daily life and retain only the most important data.

5. Consolidating what we've learned

This theory flies in the face of the reverse learning theory, by suggesting that we actually dream to remember rather than forget. It's based on a number of studies that show people remember what they've learned better if they dream after learning it . Like Zhang's theory about long-term memory storage, this theory suggests that dreams help us retain what we've learned.

The theory is bolstered by recent studies on trauma , which suggest that when people go to sleep right after a traumatic experience that they are more likely to remember and be haunted by the trauma. So one form of triage for traumatized people is to keep them awake and talking for several hours, even if they are exhausted, to prevent this traumatic memory consolidation from happening.

6. An evolutionary outgrowth of the "playing dead" defense mechanism

Based on studies that revealed strong similarities between animals who are playing dead and people who are dreaming, this theory suggests that dreaming could be related to an ancient defense mechanism: tonic immobility, or playing dead . When you dream, your brain behaves much the way it does when you're awake, with a crucial difference: chemicals like dopamine associated with movement and body activation are completely shut down. This is similar to what happens to animals who undergo temporary paralysis to fool their enemies into thinking they've died. So it's possible that dreams began as a defense mechanism which our bodies retained — in a different form — as we evolved into creatures who no longer experienced tonic immobility.

7. Threat simulation

The "playing dead" theory of dreams actually fits in nicely with another evolutionary theory of dreams, developed by philosopher-neuroscientist Antti Revonusuo in Finland . He suggests that "the biological function of dreaming is to simulate threatening events, and to rehearse threat perception and threat avoidance." People who have these kinds of dreams will be better able to face threats in their waking hours, because they've already run through these nighttime simulations. As a result, people who dream in this way will survive more often, to pass on their genes. Unfortunately, this theory doesn't explain my recurring dream of eating brownie sundaes.

8. Problem solving

Building on ideas like Revonusuo, Harvard medical researcher Deirdre Barrett suggests dreams are a kind of theater in which we're able to solve problems more effectively than when we are awake — partly because the dreaming mind makes connections more quickly than the waking mind does. This idea is based in part on experiments she did where people were asked to solve problems while "sleeping on them." The problem-solving outcomes were better for the subjects who dreamed.

9. Oneiric Darwinism

Maybe the idea of solving problems in our sleep is itself a kind of Darwinian process. Psychologist Mark Blechner says the reason we dream is:

[To] create new ideas, through partial random generation, which can then be retained if judged useful… Dreams introduce random variations into psychic life and internal narratives. They produce ‘thought mutations.’ Our minds can then select among these mutations and variations to produce new kinds of thought, imagination, self-awareness, and other psychic functions.

Basically, dreams are natural selection for ideas. This can extend to the level of emotions, too. One group of researchers suggest that dreams are places where we run through situations and try to select the most useful emotional reactions to them. Psychologist Richart Coutts suggests that this is one way we figure out the best way to react to situations emotionally , and why we often feel better about painful issues the morning after a night of dreams.

10. Processing painful emotions with symbolic associations

While a Darwinian model of dreaming suggests we are aggressively mutating our ideas, or weeding out maladaptive emotions, a new model of dreaming suggests that the process is more like therapy than evolution. We aren't aggressively selecting for the most adaptive idea or emotion — we are just running through those ideas and emotions and placing them in a broader psychological context. Often, the brain does this by associating an emotion with a symbol.

Psychiatrist and sleep disorder expert Ernest Hartmann calls this simply the Contemporary Theory of Dreaming . He writes:

When one clear-cut emotion is present, dreams are often very simple. Thus people who experience trauma—such as an escape from a burning building, an attack or a rape—often have a dream something like, "I was on the beach and was swept away by a tidal wave." This case is paradigmatic. It is obvious that the dreamer is not dreaming about the actual traumatic event, but is instead picturing the emotion, "I am terrified. I am overwhelmed." When the emotional state is less clear, or when there are several emotions or concerns at once, the dream becomes more complicated. We have statistics showing that such intense dreams are indeed more frequent and more intense after trauma. In fact, the intensity of the central dream imagery, which can be rated reliably, appears to be a measure of the emotional arousal of the dreamer. Therefore, overall the contemporary theory considers dreaming to be a broad making of connections guided by emotion.

He speculates that this kind of association between emotion and symbol helps to "tie down" the emotions and weave them into our personal history. Possibly, this kind of symbolic association was an evolutionary adaptation that helped our ancestors cope with trauma in a world where they would have dealt with far more life-threatening events on a daily basis than most of us do today.

Ultimately, this hypothesis brings us back to the storytelling component of dreams. We seem to use these bizarre images and ideas to make sense of the day's events, to turn random neural firing into something coherent, and even to figure out how we should feel about what's happened to us. There is no doubt that dreams play a major role in our thought processes. The question remains, however: Are they an evolutionary adaptation, or just an uncanny accident?

All images taken from The Fountain . Sources linked in the text.

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Freud (1900) considered dreams to be the royal road to the unconscious as it is in dreams that the ego’s defenses are lowered so that some of the repressed material comes through to awareness, albeit in distorted form.

Dreams perform important functions for the unconscious mind and serve as valuable clues to how the unconscious mind operates.

On 24 July 1895, Freud had his own dream to form the basis of his theory. He had been worried about a patient, Irma, who was not doing as well in treatment as he had hoped. Freud, in fact, blamed himself for this and was feeling guilty.

Freud dreamed that he met Irma at a party and examined her. He then saw a chemical formula for a drug that another doctor had given Irma flash before his eyes and realized that her condition was caused by a dirty syringe used by the other doctor. Freud’s guilt was thus relieved.

Freud interpreted this dream as wish fulfillment. He had wished that Irma’s poor condition was not his fault and the dream had fulfilled this wish by informing him that another doctor was at fault. Based on this dream, Freud (1900) proposed that a major function of dreams was the fulfillment of wishes.

Freud’s Interpretation of Dreams

The Interpretation of Dreams is a seminal work by Sigmund Freud, published in 1899, that introduced his theory of psychoanalysis and dream interpretation. Here’s a summary of its key points:

Introduction of Psychoanalysis : This book is where Freud first introduced his theory of psychoanalysis . This was a revolutionary approach to understanding the human mind and behavior, focusing on the role of the unconscious mind, which was largely ignored or underestimated by other theories of the time. The Interpretation of Dreams introduced key concepts of psychoanalysis such as the Oedipus complex , and free association.
Dreams as Psychological Insight : Freud proposed that dreams could provide valuable insight into an individual’s unconscious desires and conflicts. This was a novel idea, as dreams were often dismissed as meaningless or were interpreted in a more mystical or religious context.
Dreams as Wish Fulfillment : Freud proposed that dreams are a form of “wish fulfillment”. They represent the unconscious desires, thoughts, and motivations that our conscious mind represses. This concept has influenced not only the field of psychology but also literature, art, and popular culture.
Manifest and Latent Content : Freud distinguished between the manifest content of a dream (what we remember upon waking) and the latent content (the hidden psychological meaning). The manifest content is often a distorted version of the wish that the dreamer’s mind tries to fulfill, while the latent content is the underlying wish itself.
Dream Work : The process by which the unconscious mind alters the true meaning of a dream into something less disturbing is known as “dream work”. This includes mechanisms like displacement (shifting emotional significance from one object to another), condensation (combining several ideas into one), and symbolization (representing an action or idea through symbols).
Free Association : Freud used a technique called free association to uncover the latent content of dreams. In this process, a person says whatever comes to mind to a dream’s elements, leading to insights about the unconscious wishes the dream represents.

Latent Content as the Hidden Meaning of Your Dreams

Latent content in dreams, a concept introduced by Sigmund Freud in his psychoanalytic theory, refers to the hidden, symbolic, and unconscious meanings or themes behind the events of a dream.

This contrasts the manifest content, which is the actual storyline or events that occur in the dream as the dreamer remembers them.

Freud believed that the latent content of a dream is often related to unconscious desires, wishes, and conflicts. These are thoughts and feelings that are so troubling or unacceptable that the conscious mind represses them. However, they can emerge in a disguised form in our dreams.

The latent content is not directly observable because it is often coded or symbolized in the dream’s manifest content. For example, a dream about losing teeth might have a latent content related to anxiety about aging or fear of losing power or control (though interpretations can vary greatly depending on the individual).

How the Mind Censors Latent Content

Sigmund Freud proposed that the mind uses a process called “dream work” to censor or disguise the latent content of a dream. The latent content, which represents our unconscious wishes and desires, is often disturbing or socially unacceptable.

The purpose of dreamwork is to transform the forbidden wish into a non-threatening form, thus reducing anxiety and allowing us to continue sleeping.

Dreamwork involves the process of condensation, displacement, and secondary elaboration:

Displacement : This involves shifting the emotional significance from an important object to a less important one. Displacement takes place when we transform the person or object we are really concerned about to someone else. For example, one of Freud’s patients was extremely resentful of his sister-in-law and used to refer to her as a dog, dreaming of strangling a small white dog. Freud interpreted this as representing his wish to kill his sister-in-law. If the patient would have really dreamed of killing his sister-in-law, he would have felt guilty. The unconscious mind transformed her into a dog to protect him.
Condensation : This is the process of combining several ideas or people into a single dream object or event. For example, a dream about a man may be a dream about both one’s father and one’s lover. A dream about a house might be the condensation of worries about security as well as worries about one’s appearance to the rest of the world.
Symbolization : This is the representation of a repressed idea or wish through symbols. For example, a dream about climbing a ladder might symbolize ambition or a desire for success.
Secondary Elaboration : Secondary elaboration occurs when the unconscious mind strings together wish-fulfilling images in a logical order of events, further obscuring the latent content. It can involve adding details or creating a storyline that connects the different elements of the dream. According to Freud, this is why the manifest content of dreams can be in the form of believable events.

These mechanisms work together to transform the latent content into the manifest content, allowing the dreamer to remain asleep and unaware of the disturbing or unacceptable thoughts and desires expressed in the dream.

However, through techniques like free association and dream analysis, Freud believed that it was possible to uncover the latent content and gain insight into the unconscious mind .

Psychoanalytic Dream Interpretation

Sigmund Freud developed several techniques to uncover the latent content of dreams, which he believed represented the unconscious desires and conflicts of the dreamer. Here are the main techniques:

Free-Association

Freud used a technique called free association to uncover the latent content of dreams. In this process, a person says whatever comes to mind in relation to each element of the dream, without censoring or judging their thoughts.

In free association, the individual is encouraged to share any thoughts that come to mind about each element of the dream, no matter how random or unconnected they may seem.

The idea is that these associations can lead to insights into the unconscious wishes or conflicts that the dream represents.

Transference

Transference is a process where the feelings and desires that the individual has towards significant people in their life are transferred onto the therapist.

Observing these transference patterns can provide clues about the latent content of the individual’s dreams.

Dream Analysis

This involves a detailed examination of the dream’s content. The analyst and the individual work together to explore the dream’s manifest content (the actual events of the dream) and try to understand what these might symbolize in terms of the dreamer’s unconscious desires or conflicts (the latent content).

Symbol Interpretation

In Freud’s later work on dreams, he explored the possibility of universal symbols in dreams . Some of these were sexual, including poles, guns, and swords representing the penis and horse riding and dancing representing sexual intercourse.

For example, Freud suggested that dreams of flying might represent sexual desire, while dreams of losing teeth might represent anxiety about aging.

However, he also emphasized that the meaning of symbols can vary greatly between individuals, and that the individual’s associations are the most important factor in interpretation.

However, Freud was cautious about symbols and stated that general symbols are more personal rather than universal. A person cannot interpret what the manifest content of a dream symbolizes without knowing about the person’s circumstances.

“Dream dictionaries”, which are still popular now, were a source of irritation to Freud. In an amusing example of the limitations of universal symbols, one of Freud’s patients, after dreaming about holding a wriggling fish, said to him “that’s a Freudian symbol – it must be a penis!”

Freud explored further, and it turned out that the woman’s mother, who was a passionate astrologer and a Pisces, was on the patient’s mind because she disapproved of her daughter being in analysis. It seems more plausible, as Freud suggested, that the fish represented the patient’s mother rather than a penis!

Consideration of Repression

Freud believed that repressed desires and conflicts often emerge in dreams, so understanding what the individual might be repressing can help to interpret the dream’s latent content.

Freud, S., & Strachey, J. (1900). The interpretation of dreams (Vol. 4, p. 5). Allen & Unwin.

Republicans are using Tyson’s decision to hire migrants to push their “Great Replacement” lie

Senator jd vance says the meatpacker is participating in the "decimation of the american dream.” , by ashlie d. stevens, published march 19, 2024 12:00pm (edt), updated march 19, 2024 1:43pm (edt).

Leadership from Tyson Foods announced last week they would be shuttering one of the company’s pork plants in Perry, Iowa. It’s not great news for a town that is home to just over 7,800 people, however the shutdown comes after news of over ten similar closures that punctuated a year of record losses for the pork industry; in 2023, there was average loss for producers of about $32 per hog .

The same day Tyson made that announcement, the head of the company’s social efforts division, Garret Dolan, appeared in an article by Bloomberg with the headline “ Tyson Is Hiring New York Immigrants for Jobs No One Else Wants .” The story details how companies like Tyson are struggling to fill what they characterize as “unpleasant jobs” with a US unemployment rate of 3.9%. As a result, the meatpacker is joining the nonprofit Tent Partnership for Refugees with a plan to hire some of the nearly 200,000 migrants who have come through New York City’s intake system over the past two years.

In the article, Dolan stated that Tyson “would like to employ another 42,000 [immigrants] if we could find them.”

Currently, according to Bloomberg, Tyson already employs about 42,000 immigrants among its 120,000-member American workforce, which is very likely why he invoked that specific number. However, in light of the news out of Perry, some top-level Republicans — including Ohio senator and potential Trump running mate JD Vance — are spinning a narrative wherein Americans are being replaced with thousands of migrant workers, leading some to refer to the situation as “‘The Great Replacement’ in motion.”

Strands of Great Replacement theory , sometimes also called the “white genocide” theory, originated in the late 19th century, but the concept was introduced to the wider contemporary public through the release of French author Renaud Camus ’ 2011 book “Le Grand Replacement..” The theory, which has gained significant popularity in alt-right circles, argues that there is some deliberate plot among global leaders to replace white populations in Western countries with non-white immigrants.

According to the Anti-Defamation League , “the ‘great replacement’ philosophy was quickly adopted and promoted by the white supremacist movement, as it fit into their conspiracy theory about the impending destruction of the white race, also know as ‘white genocide.’ It is also a strong echo of the white supremacist rallying cry, ‘the 14 words:’ ‘We must secure the existence of our people and a future for white children.’”

The theory has been widely discredited by scholars and experts, who argue that it is a lie based on racist and xenophobic beliefs rather than factual evidence. Despite this, it continues to influence extremist ideologies and has been linked to acts of violence and terrorism. For example, Payton S. Gendron, who killed 10 in a 2022 mass shooting at a Buffalo supermarket , allegedly wrote “a 180-page document filled with hateful rants about race and ties to the ‘great replacement,” according to NPR .

Sometimes, like in the case of chatter on social media about the Tyson situation, references to the theory are more straightforward. For instance, one YouTube video from the conservative account Pinball Preparedness, which has 109,000 subscribers, is literally titled: “ The Great Replacement Theory in Action .”

“Well, Tyson Foods just did it,” the video description read. “They are getting rid of American workers and openly admitting they are trying to hire Illegals to replace them. Get ready, your stores, schools, communities...are all about to have you living as the problem if we let this continue.”

" All we know is that they are firing American workers and hiring illegal aliens to replace them. "

However, sometimes Republicans’ allusions to the theory in public are a little more muted, though they are meant to stoke similar fears among their followers. For instance, Senator Vance appeared on Fox News’ “Jesse Watters Primetime” on Thursday and suggested that Tyson was complicit in the “decimation of the American dream.”

"All we know is that they are firing American workers and hiring illegal aliens to replace them,” Vance said. “This is the entire point of illegal immigration — and Republicans, we've got to hammer this point home."

This is, of course, despite the fact that studies from the Pew Research Center shows that Americans generally agree that immigrants, whether undocumented or living legally in the country, mostly “do not work in jobs that U.S. citizens want” which a majority saying so across racial and ethnic groups and among both political parties. According to a 2020 survey, about 77% of adults say undocumented immigrants mostly fill jobs U.S. citizens do not want. Remember the title of that Bloomberg article? “Tyson Is Hiring New York Immigrants for Jobs No One Else Wants.”

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In this case, Republicans’ “Great Replacement” narrative also assumes that all the Tyson plant employees who are losing their jobs in Perry are white. According to r eports from NPR , Perry is one of only four communities in Iowa where Latinos make up at least one third of the population, many of whom were drawn there specifically for manufacturing and factory jobs. Local news reports indicate that the Perry Latino community is deeply impacted by the news.

Knock and Drop Iowa, a nonprofit organization based in Des Moines, is raising money to help support the employees who will be out of a job on June 28, the plant’s last official day. "We know that there's a lot of Latino families — they work at Tyson," Zuli Garcia, the organization’s founder, said in an interview with KCCI Des Moines .

Garcia continued: "That's their place. That's where they live. That's where they work. That's their home."

In a statement emailed to Salon Food, a representative from Tyson said that there has been a lot of misinformation in the media about their company and "felt compelled to set the record straight."

"Any insinuation that we would cut American jobs to hire immigrant workers is completely false," they said. "Tyson Foods is strongly opposed to illegal immigration, and we led the way in participating in the two major government programs to help employers combat unlawful employment, E-Verify and the Mutual Agreement between Government and Employers (IMAGE) program."

They continued: "Since being founded in 1935 in Arkansas, Tyson Foods has created jobs and employed millions of people in states all across America, the majority of whom are American citizens. Today, Tyson Foods employs 120,000 team members in the United States, all of whom are required to be legally authorized to work in this country. We have a history of strong hiring practices, and anybody who is legally able is welcome to apply to open job listings.”

Update: This story has been updated with a statement from Tyson.

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Ashlie D. Stevens is Salon's food editor. She is also an award-winning radio producer, editor and features writer — with a special emphasis on food, culture and subculture. Her writing has appeared in and on The Atlantic, National Geographic’s “The Plate,” Eater, VICE, Slate, Salon, The Bitter Southerner and Chicago Magazine, while her audio work has appeared on NPR’s All Things Considered and Here & Now, as well as APM’s Marketplace. She is based in Chicago.

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In October 2022, amid a flurry of media appearances promoting their film “Tàr,” the director Todd Field and the star Cate Blanchett made time to visit a cramped closet in Manhattan. This closet, which has become a sacred space for movie buffs, was once a disused bathroom at the headquarters of the Criterion Collection, a 40-year-old company dedicated to “gathering the greatest films from around the world” and making high-quality editions available to the public on DVD and Blu-ray and, more recently, through its streaming service, the Criterion Channel. Today Criterion uses the closet as its stockroom, housing films by some 600 directors from more than 50 countries — a catalog so synonymous with cinematic achievement that it has come to function as a kind of film Hall of Fame. Through a combination of luck, obsession and good taste, this 55-person company has become the arbiter of what makes a great movie, more so than any Hollywood studio or awards ceremony.

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Why Do We Dream? Top Dream Theories
Some of the more prominent dream theories contend that the function of dreaming is to: Consolidate memories. Process emotions. Express our deepest desires. Gain practice confronting potential dangers. Many experts believe that we dream due to a combination of these reasons rather than any one particular theory.
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In our "defensive activation theory," dream sleep exists to keep neurons in the visual cortex active, thereby combating a takeover by the neighboring senses. In this view, dreams are primarily ...
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Dreams are mental, emotional, or sensory experiences that take place during sleep. Sleep experts continue to study what happens in the brain during sleep, but no one knows for sure why we dream. Dreams are the most common and intense during REM sleep when brain activity increases. Dreaming is normal and healthy, but frequent nightmares can ...
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The Science Behind Dreaming. New research sheds light on how and why we remember dreams--and what purpose they are likely to serve. By Sander van der Linden. Credit: Getty Images. Neuroscience ...
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Meaning in dreams, he says, is basically a side effect. "I don't think dogs are imbuing their dreams with meaning, but they still dream," he says. "Humans can imbue their dreams with meaning, but dreams should still have a purpose for all mammals who regularly do it," Hoel says. It's also true, he says, that "evolution is a great ...
Activation Synthesis Model of Dreaming
The activation-synthesis theory is a neurobiological explanation of why we dream. The question of why people dream has perplexed philosophers and scientists for thousands of years, but it is only fairly recently in history that researchers have been able to take a closer look at exactly what happens in the body and brain during dreaming.
The science of dreams
The question of why we dream was more difficult to answer. Nevertheless, a 1978 review of sleep and dreams did attempt to address this question. The second half, on dreaming, was written by Rosalind Cartwright. As one of the first women to work in this area, she was often called the "queen of dreams." ... Another theory about why we dream ...
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Dreaming is the far end of this continuum: the state in which we make connections most loosely. Some consider this loose making of connections to be a random process, in which case dreams would be ...
Why Do We Dream? A New Theory on How It Protects Our Brains
A New Theory on How It Protects Our Brains - David Eagleman. Eagleman DM, Vaughn DA (2020). The defensive activation theory: dreaming as a mechanism to prevent takeover of the visual cortex. Front Neurosci. 2021 May 21;15:632853. doi: 10.3389/fnins.2021.632853. When he was two years old, Ben stopped seeing out of his left eye.
The Science of Dreams
The Science of Dreams. Published 29 Apr 2022. Author Charlotte Stoddart. Source Knowable Magazine. Freud thought that dreams were the gateway to our unconscious mind. Today, many scientists think the opposite: that the dreaming brain is quite similar to our awake, conscious state. But dreaming is a very personal experience and one that we can ...
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There are many theories about why we dream: the threat-simulation theory sees dreaming as an evolutionary "practice ground" for dealing with threats; the expectation-fulfillment theory says that we use up emotional energy during the night; the activation-synthesis theory claims that dreams are meaningless interpretations of random firings ...
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A related theory maintains that the function of dreams is to clear the brain of its excess baggage—for example, by deleting unnecessary memories. And some experts believe that dreams are a ...
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Information-Processing Theory and the Self-Organization Model. Similarly, information-processing theory suggests dreams are just a part of our cognitive development. Cognitive psychology looks at how the brain makes decisions, solves problems, and stores memories. Memory storage is key to this study and why we dream.
Dreams and Dreaming
This entry provides an overview of major themes in the philosophy of sleep and dreaming, with a focus on Western analytic philosophy, and discusses relevant scientific findings. 1. Dreams and epistemology. 1.1 Cartesian dream skepticism. 1.2 Earlier discussions of dream skepticism and why Descartes' version is special.
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Theories of dreaming span scientific disciplines, from psychiatry and psychology to neurobiology. Some current theories suggest that dreaming is: A component and form of memory processing, aiding ...
Why Do We Dream?
Dreams Are Wish Fulfilments. Sigmund Freud thought that his theory of dreams was his most valuable discovery, important for giving a scientific explanation of why people dream and also for ...
Why We Dream and the Role They Play
However, the prevailing theory is that dreaming helps you consolidate and analyze memories (like skills and habits) and likely serves as a "rehearsal" for various situations and challenges ...
10 Scientific Theories About Why We Dream
6. The Tonic Immobility Reflex. According to one theory, dreams are a byproduct of the body paralyzing itself as a defense mechanism during sleep. The tonic immobility reflex, or "playing dead," is used by many mammals and reptiles as a last line of defense against predators.
Why Do We Dream? Maybe to Ensure We Can Literally 'See' the World upon
A more recent theory suggests nighttime dreams protect visual areas of the brain from being co-opted during sleep by other sensory functions, such as hearing or touch.
10 theories that explain why we dream
They flash through our minds as dreams before we secret them away in the files of our memory. 4. Garbage collection. Dubbed the "reverse learning" theory, this idea suggests that we dream to get ...
Why Do We Dream? 3 of the Most Interesting Theories to Consider
In his infamous 1899 book 'The Interpretation of Dreams', Freud argued that dreams represent our unconscious wishes and desires. The basis of his theory is that most of our desires are perfectly innocent. However, some are so inappropriate or unacceptable to our conscious self that we bury them in our subconscious. They resurface in our dreams.
Sigmund Freud Dream Theory
Latent content in dreams, a concept introduced by Sigmund Freud in his psychoanalytic theory, refers to the hidden, symbolic, and unconscious meanings or themes behind the events of a dream. This contrasts the manifest content, which is the actual storyline or events that occur in the dream as the dreamer remembers them.
Republicans are using Tyson's decision to hire migrants to push their
Strands of Great Replacement theory, sometimes also called the "white genocide" theory, originated in the late 19th century, but the concept was introduced to the wider contemporary public ...
The Sunday Read: 'Sure, It Won an Oscar. But Is It Criterion?'
We want to hear from you. Tune in, and tell us what you think. Email us at [email protected]. Follow Michael Barbaro on X: @mikiebarb.

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Republicans are using Tyson’s decision to hire migrants to push their “Great Replacement” lie