activation synthesis hypothesis psychology definition

Activation Synthesis Theory

Sleep discussions generally focus on why we sleep, what happens if we don't get enough sleep, sleep disorders, and even the stages of sleep. But, have you ever wondered why we dream and what any of those dreams we have mean? This is where the Activation Synthesis theory comes in.

The Activation Synthesis theory is the activation of specific brain regions, and its synthesis is what causes dreams. There are bursts of neural activity that stem from the brain cell through the cerebral cortex that, causes the frontal lobe to interpret those signals and give them meaning.

Generally, it is well-known that dreaming comes in the stage of REM. However, are dreams actually significant? Do they have some kind of meaning to them, or is it just something that takes place in the brain and is neurologically based? This has always been something that most people have been fascinated with. Here's all you need to know about the Activation Synthesis theory.

What Is The Activation Synthesis Theory?

The Activation Synthesis theory is generally one of the simplest that most people tend to overthink, or in most cases, they find the term somewhat intimidating. However, the key is understanding what the terms activation and synthesis mean separately. Once that understanding is there, the theory basically speaks for itself.

That is not to say that the model is not complicated. Simply put, activation means that areas of the brain are being used. Then humans need to synthesize or process that information into something that makes sense to us.

The encoding and processing of data are one of sleep's goals. The information from our conscious mind is moved from temporary to permanent memory in the brain during non-REM sleep. Data transfers from the subconscious mind to the long-term memory during REM sleep. During these processes, dreams happen.

Unlike Freud's Wish-Fulfillment or the Information Processing theory, which agrees that dreams have a meaning and a purpose, the Activation Synthesis theory pretty much says the exact opposite. This theory states that dreams are absolutely meaningless.

This theory even further states that dreams are a side effect and do not have a purpose. So, if they are meaningless, then how do they occur? The Activation Synthesis theory theorizes that dreams simply start off as random electrical activation. This random electrical activation originates from the brain stem.

Brain scans have proven that a lot of activity comes from the brain stem when we are in REM while we sleep. For example, the frontal lobe does not stop working in the reticular formation, medulla, etc. The bursts of neural activity that occur when you are asleep are proof of that activity.

Why is the fact that the frontal lobe does not stop working important? This is because the frontal lobe is responsible for interpreting and also creating meanings and those different situations you dream of. Therefore, while we are in REM, the frontal lobe interprets all the bursts of neural activity that come from the brain stem. The frontal lobe is basically just carrying out its function.

Hence why theorists state that dreams are a side effect as the frontal lobe doing its job of interpreting and creating meaning is considered as a side effect of what is happening in your brain stem. Therefore, there is no meaning or any kind of symbolism attached to dreams. [1]

Why Is The Activation Synthesis Theory Well-Liked?

This theory is well-liked because it helps explain why we can have the weirdest dreams that make no sense. Therefore, if you've had dreams that you have had no way of explaining, this theory is the best in getting you to realize that your dream is just that, a dream. There is no deeper meaning or logic to that dream.

There is one other thing that this theory explains: why, every now and then, you can get random noises outside of our dreams making their way into our dream. For example, if someone is knocking on your door in real life and that noise somehow makes its way into your dream. This is how you wake up thinking about how you were dreaming about knocking, and now someone is knocking on your door.

This is simply because the senses don't stop working when you fall asleep. This is easily proven by how you can feel when someone touches your arm while sleeping. The information from outside of your dream is still making its way to your brain, and the frontal lobe will still interpret that sound and whatever else you were dreaming about.  

Therefore, the brain stem activity is the activation part, and the cerebral cortex tries to make sense of what is happening in the synthesis part. [1]

What Is The History Of The Activation Synthesis Theory?

As with almost anything, there is a history to how certain terms came about. The Activation Synthesis theory is no exception. Two individuals in the Department of Psychiatry at Harvard Med School, namely Hobson and McCarley, described the Activation Synthesis model in the 1970s.

This is a model of dreaming, which happens to be an extension of the REMs cycling model. Before this, there are records of Babylonians that go as far back as 5000 years ago, clearly keeping track of dreams and recording them on clay pots. Not only that but also trying to interpret them.

That is still the case in this day and age. There is a list compiled numbering what a dream you had could potentially mean. Some people even use that very same dream list to bet in the lottery. Furthermore, Egyptians actually had a dream God statue they worshiped.

This theory has undergone many revisions over the years since it was created. The revisions happened due to the fact that as the years went by, humans started having increased knowledge of the brain, thanks to technology. The more is learned about the brain, the more theories that are physiologically and neurologically based are further developed. [1]

What Are The Weaknesses Of The Activation Synthesis Theory?

Theories can typically explain things only so far. There will always be some aspect that they cannot quite explain or prove thoroughly. This is the case with the Activation Synthesis Theory, as there are some holes in the theory that dreams have no meaning.

One such weakness is that this theory still does not explain why the frontal lobe in our brain chooses to interpret the activity stemming from the brain stem in the way that they do. I mean, why is a burst of neural activity being interpreted as a mystical creature kind of dream? How did the frontal lobe get to that?

Furthermore, we may have the very same neural activity at night. Still, each frontal lobe may choose to interpret that burst of electrical activity in different ways. This theory cannot explain why the frontal lobe may interpret the neural activity into different imagery for different people even when they have the same burst of neural activity when asleep.

Some other criticisms of this theory are that some people simply don't dream or people that dream but aren't necessarily in REMs sleep. Therefore, some argue that the Activation Synthesis Theory is far too limited as it theorizes that we can only dream in REMs sleep. Also, some feel that it is simply too neurological to truly explain what our dreams are all about.

There is evidence that animals also dream in their sleep. If you're a dog owner, I'm sure you've seen what looks like your dog running in their sleep. That's because they dream of running in their sleep. However, there is no definitive to truly say that it can be fully proven.

Some people feel that because it is mainly based on animal research, it is highly possible that it may not apply to humans as we do not function the exact same way, even though animals typically studied have a similar nervous system.

Furthermore, some FMRI evidence has suggested that the initiation of dreaming occurs in the cerebral cortex and not the brain stem. Ultimately, this dream theory, along with the other, doesn't truly explain why we dream in a way that gives it justice.  [2]

Activation Synthesis In People With Brain Stem Damage

Studies have been conducted on people who have sustained damage to their brain stems. It has been proven that their bursts of neural activity firing from the brain stem are actually not the same as what a person who hasn't sustained damage to their brain stem would be.

However, these people with damaged brain stems are still dreaming. Dreaming does not stop just because the brain stem is damaged. As dreaming still occurs when a brain stem is damaged, and neural activity is still being fired off, the Activation Synthesis Theory is still in effect. [3]

What Happens If The Frontal Lobe Is Damaged?

The brain comprises four lobes, one of them being the frontal lobe. Each lobe has a different function and also controls different behaviors. Unfortunately, the frontal lobe is one of those lobes that is more susceptible to damage as there happen to be many more bony prominences at the front of the skull.

An injury to the frontal lobe will affect the ability to multitask and judgment, but this does not affect dreaming. The science is still up in the air. Still, some evidence suggests that the hippocampus, situated deep inside the temporal lobe, plays a role in dreams.

However, it isn't clear if dreaming stops when the hippocampus is damaged. More research is still to be conducted into whether or not the anatomy linked to the Activation Synthesis Theory stops dreaming when damaged. [5]

What Happens If One Has A REMs Sleep Disorder?

When evaluating the Activation Synthesis Theory, there is one aspect that is particularly interesting as this theory is all about REMs sleep. When focusing on people who do not get the switch of commands, you realize that their brain stem is not damaged and is very active and still sending signals to the brain to alert it to the fact that that individual is in REMs sleep.

However, the muscles just don't comprehend that and, therefore, do not get that switch-off command. This is called a REMs sleep disorder. The subcoeruleus nucleus, a tiny cluster of cells located in the brain stem, regulates REM sleep. Individuals don't really undergo the muscle paralysis linked with REM sleep once those cells are damaged or ill.

This can result in REM sleep behavior disorder, a dangerous condition in which those affected violently play out their dreams. So, what happens when this is the case? Those with this disorder act out what they are dreaming as if they are awake. Take the example mentioned above of a dog acting out running in their sleep. 

Although it is usually certain animals that are more likely to do this. There are humans that have this disorder. There are humans that sleep talk, sleepwalk, sleep eat, etc., but that is not necessarily the disorder. Humans with REMs sleep disorder experience physical, violent outbursts during sleep.

Since the discovery of REMs sleep disorder, research has revealed that three degenerative brain illnesses affect the majority of these patients. The most prominent one happens to be Parkinson's disease, a motor system-affected degenerative condition that occurs in the central nervous system.

Dementia is another type of brain illness caused by REMs disorder. Symptoms include forgetfulness, erratic alertness, visual hallucinations, and difficulty walking. The other well-known condition is multiple system atrophy. This brain illness is known to affect the area of the nervous system that regulates both voluntary and involuntary motions, such as digestion. [4]

People generally have an innate hunger to figure out what dreams mean. Psychologists still aren't 100 percent sure why we dream. Still, there have been several theories that are credible and accepted, one being the Activation Synthesis theory.

Dreams are generally just our brains trying to find meaning in the random signals that the brain stem keeps firing according to the Activation Synthesis Theory. Therefore, trying to put meaning to them is pointless as it all simply has to do with the interpretation of the neural activity.

• https://www.verywellmind.com/what-is-the-activation-synthesis-model-of-dreaming-2794812
• https://dreams.ucsc.edu/Library/domhoff_2000e.html
• https://my.clevelandclinic.org/health/body/21598-brainstem
• https://www.mayoclinic.org/diseases-conditions/rem-sleep-behavior-disorder/symptoms-causes/syc-20352920#:~:text=Rapid%20eye%20movement%20(REM)%20sleep,sometimes%20called%20dream%2Denacting%20behavior .
• https://www.healthline.com/health/frontal-lobe#:~:text=As%20a%20whole%2C%20the%20frontal,concentrating%20or%20planning%2C%20and%20impulsivity.

Related posts:

• Why Do We Dream? (6 Theories and Psychological Reasons)
• Sleep Stages (Light, Deep, REM)
• Cerebral Cortex (Location, Function, Images)
• Where is the Primary Visual Cortex Located?
• Orbitofrontal Cortex

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Activation-Synthesis Hypothesis

The Activation-Synthesis Hypothesis is a theory in psychology that seeks to explain the nature and purpose of dreams. According to this hypothesis, dreams are a result of random brain activity during the rapid eye movement (REM) stage of sleep, which is accompanied by vivid dreaming.

Understanding the Activation-Synthesis Hypothesis

The Activation-Synthesis Hypothesis was proposed by J. Allan Hobson and Robert McCarley in 1977 as an alternative explanation to the psychoanalytic theories put forth by Sigmund Freud. While Freud believed that dreams were a reflection of unconscious desires and wishes, the Activation-Synthesis Hypothesis suggests that dreams have no inherent meaning or purpose.

According to this theory, the brain activates various neural circuits during REM sleep, causing random firing of neurons in the brainstem. This random neural activity then stimulates the higher-level brain regions responsible for thinking and perception, such as the cortex. As a result, the brain attempts to make sense of these random signals, leading to the creation of dreams.

Examples of Activation-Synthesis Hypothesis

To illustrate the Activation-Synthesis Hypothesis, consider the following examples:

• Example 1: A person dreams of flying through the sky and experiencing a sense of weightlessness. According to the hypothesis, this dream may be a result of random activation of brain circuits associated with movement and sensory perception.
• Example 2: In another dream, someone finds themselves in a chaotic and unfamiliar environment. This dream could be a product of the brain attempting to piece together unrelated fragments of neural activity to create a coherent narrative.

Critiques and Supporting Evidence

While the Activation-Synthesis Hypothesis offers an alternative perspective on dreaming, it is not without its critics. Some researchers argue that dreams may indeed carry symbolic meanings or represent unconscious desires, contradicting the idea that they are purely random manifestations.

However, proponents of the theory highlight various supporting evidence. For instance, brain imaging studies have shown increased activity in the brainstem and decreased activity in the prefrontal cortex during REM sleep, suggesting a connection between neural activation and dream experiences.

The Importance of Understanding Dreams

Regardless of whether one supports the Activation-Synthesis Hypothesis or not, dreams remain an intriguing subject of study in psychology . They provide a window into our subconscious mind, allowing us to explore hidden thoughts, emotions, and memories that may influence our waking lives.

Moreover, dreams can also serve as sources of inspiration, creativity, and problem-solving. Numerous artists, writers, and scientists have attributed their breakthrough ideas to insights gained from their dreams.

The Activation-Synthesis Hypothesis proposes that dreams arise from random brain activity during REM sleep. Rather than being purposeful messages or manifestations of our unconscious desires, dreams may simply be the brain’s attempt to make sense of the chaotic neural firing occurring during this stage of sleep. By exploring this hypothesis and studying dreams further, we can gain a deeper understanding of the complexities of the human mind and the role of sleep in psychological processes.

July 26, 2011

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

Getty Images

For centuries people have pondered the meaning of dreams. Early civilizations thought of dreams as a medium between our earthly world and that of the gods. In fact, the Greeks and Romans were convinced that dreams had certain prophetic powers. While there has always been a great interest in the interpretation of human dreams, it wasn’t until the end of the nineteenth century that Sigmund Freud and Carl Jung put forth some of the most widely-known modern theories of dreaming. Freud’s theory centred around the notion of repressed longing -- the idea that dreaming allows us to sort through unresolved, repressed wishes. Carl Jung (who studied under Freud) also believed that dreams had psychological importance, but proposed different theories about their meaning.

Since then, technological advancements have allowed for the development of other theories. One prominent neurobiological theory of dreaming is the “activation-synthesis hypothesis,” which states that dreams don’t actually mean anything: they are merely electrical brain impulses that pull random thoughts and imagery from our memories. Humans, the theory goes, construct dream stories after they wake up, in a natural attempt to make sense of it all. Yet, given the vast documentation of realistic aspects to human dreaming as well as indirect experimental evidence that other mammals such as cats also dream, evolutionary psychologists have theorized that dreaming really does serve a purpose. In particular, the “threat simulation theory” suggests that dreaming should be seen as an ancient biological defence mechanism that provided an evolutionary advantage because of  its capacity to repeatedly simulate potential threatening events – enhancing the neuro-cognitive mechanisms required for efficient threat perception and avoidance.

So, over the years, numerous theories have been put forth in an attempt to illuminate the mystery behind human dreams, but, until recently, strong tangible evidence has remained largely elusive.

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Yet, new research published in the Journal of Neuroscience provides compelling insights into the mechanisms that underlie dreaming and the strong relationship our dreams have with our memories. Cristina Marzano and her colleagues at the University of Rome have succeeded, for the first time, in explaining how humans remember their dreams. The scientists predicted the likelihood of successful dream recall based on a signature pattern of brain waves. In order to do this, the Italian research team invited 65 students to spend two consecutive nights in their research laboratory.

During the first night, the students were left to sleep, allowing them to get used to the sound-proofed and temperature-controlled rooms. During the second night the researchers measured the student’s brain waves while they slept. Our brain experiences four types of electrical brain waves: “delta,” “theta,” “alpha,” and “beta.” Each represents a different speed of oscillating electrical voltages and together they form the electroencephalography (EEG). The Italian research team used this technology to measure the participant’s brain waves during various sleep-stages. (There are five stages of sleep; most dreaming and our most intense dreams occur during the REM stage.) The students were woken at various times and asked to fill out a diary detailing whether or not they dreamt, how often they dreamt and whether they could remember the content of their dreams.

While previous studies have already indicated that people are more likely to remember their dreams when woken directly after REM sleep, the current study explains why. Those participants who exhibited more low frequency theta waves in the frontal lobes were also more likely to remember their dreams.

This finding is interesting because the increased frontal theta activity the researchers observed looks just like the successful encoding and retrieval of autobiographical memories seen while we are awake. That is, it is the same electrical oscillations in the frontal cortex that make the recollection of episodic memories (e.g., things that happened to you) possible. Thus, these findings suggest that the neurophysiological mechanisms that we employ while dreaming (and recalling dreams) are the same as when we construct and retrieve memories while we are awake.

In another recent study conducted by the same research team, the authors used the latest MRI techniques to investigate the relation between dreaming and the role of deep-brain structures. In their study, the researchers found that vivid, bizarre and emotionally intense dreams (the dreams that people usually remember) are linked to parts of the amygdala and hippocampus. While the amygdala plays a primary role in the processing and memory of emotional reactions, the hippocampus has been implicated in important memory functions, such as the consolidation of information from short-term to long-term memory.

The proposed link between our dreams and emotions is also highlighted in another recent study published by Matthew Walker and colleagues at the Sleep and Neuroimaging Lab at UC Berkeley, who found that a reduction in REM sleep (or less “dreaming”) influences our ability to understand complex emotions in daily life – an essential feature of human social functioning.  Scientists have also recently identified where dreaming is likely to occur in the brain.  A very rare clinical condition known as “Charcot-Wilbrand Syndrome” has been known to cause (among other neurological symptoms) loss of the ability to dream.  However, it was not until a few years ago that a patient reported to have lost her ability to dream while having virtually no other permanent neurological symptoms. The patient suffered a lesion in a part of the brain known as the right inferior lingual gyrus (located in the visual cortex). Thus, we know that dreams are generated in, or transmitted through this particular area of the brain, which is associated with visual processing, emotion and visual memories.

Taken together, these recent findings tell an important story about the underlying mechanism and possible purpose of dreaming.

Dreams seem to help us process emotions by encoding and constructing memories of them. What we see and experience in our dreams might not necessarily be real, but the emotions attached to these experiences certainly are. Our dream stories essentially try to strip the emotion out of a certain experience by creating a memory of it. This way, the emotion itself is no longer active.  This mechanism fulfils an important role because when we don’t process our emotions, especially negative ones, this increases personal worry and anxiety. In fact, severe REM sleep-deprivation is increasingly correlated to the development of mental disorders. In short, dreams help regulate traffic on that fragile bridge which connects our experiences with our emotions and memories.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist at the Boston Globe. He can be reached at garethideas AT gmail.com or Twitter @garethideas .

AP Psychology Community

AP Psychology Study Resource: Definition Of Activation Synthesis Theory

It’s no secret that, as a species, humans are obsessed with the process of dreaming.

We write poems and songs about it. We even have movies about it. A simple google search about dreaming results in thousands of websites where people share their dreams or talk about what their dream interpretations could be.

There are even certain self-proclaimed psychics who claim dreams are a way to see the future.

What’s odd is that there are common dreams, such as teeth falling out or somehow going to work and forgetting to wear clothes. We have all struggled with these silly dreams at one point or another, but how many of us actually understand why?

This is something scientists are continuously trying to figure out. There are a variety of theories about what causes the process of dreaming, although they are all, as of yet, unproven.

One of the most common theories behind dreaming is the Activation Synthesis Theory.

Had Any Good Dreams Lately?

The activation-synthesis theory is a theory based on neurobiological studies into the reasons why we dream.

Since the beginning of time, people have been confused by the process of dreaming. At one point, dreams were alleged to be the chosen method of communication with people from angels or the gods.

Over time, as scientific advancements were made, people began to look at the process of dreaming more skeptically.

Among the people that began to look at dreaming more skeptically were a couple of Harvard neuroscience students named Allan Hobson and Robert McCarley.

Allan Hobson and Robert McCarley were the scientists that first proposed the Activation Synthesis Theory. In 1977, they released a hypothesis that dreaming is caused by the brain trying to make sense of the activity that is still taking place in the brain during sleep.

The brain is the only part of our body that does not rest when we are sleeping. In fact, the brain is always acting at a remarkably high level. The difference when we sleep, according to the hypothesis from Hobson and McCarley, is that the parts of the brain that normally control bodily functions like walking and chewing are now free to take over some of the responsibility of thinking.

How Does Activation Synthesis Work?

The activation synthesis theory is the suggestion that our dreams are caused by these enhanced processes of the brain, which occur when our brain is working entirely on the process of thought. People used to think that sleeping meant we were in a completely passive state. We now know that sleeping is probably the most active period of the day for our brains.

In fact, the brain is almost in overdrive during the time we are sleeping. Our brains work almost like a computer during this time. They are sorting through the activities of the previous day, “filing away” the things we have learned, and making sense of the parts of the day that might have been confusing or overly stressful for us. You might find yourself asking, though, how any of this relates to dreaming.

According to Hobson, when our brains hit the REM cycle of sleeping, our brain begins to sort through the limbic system, which is responsible for emotions, memories, and other such sensations. This is when the process of “making sense” of our thoughts and feelings begins.

Another suggestion from Hobson was that there are five characteristics to dreams that result from this process.

Dreams Are Illogical

Have you ever dreamed you were at dinner with a variety of people that otherwise would not be joining you for dinner? Have you ever dreamed that you went to visit a relative who has passed away? Have you ever dreamed that you were driving a car underwater or flying? Most people have experienced these kinds of ridiculous alternate “realities” while in a dream state.

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6 The Activation-Synthesis Theory of Dreaming

• Published: September 2017
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This chapter provides the most detailed critical analysis yet developed of the neurophysiological theory of dreaming called activation-synthesis theory, a bottom-up theory that rejects a top-down neurocognitive approach because rigorous studies of dream content allegedly cannot be carried out, especially on the basis of dream reports collected in the sleep lab. This theory suggests that dreams may be “cognitive trash.” The chapter draws on detailed neurophysiological evidence little known outside of neurophysiology, and hardly at all among dream researchers, to show that all of the empirical claims put forth by activation-synthesis theorists in 1977 had been shown to be wrong by the mid-1980s, with further evidence for this refutation appearing in the 2000s due to methodological and technical advances. Similarly, the studies of dream content by activation-synthesis theorists have major flaws and are contradicted by most of the findings presented in earlier chapters.

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Activation-synthesis theory (Hobson and McCarley 1977)

In this post

Unlike other research about sleep and dreaming, Hobson and McCarley’s theory focuses specifically on the neurobiological aspects of this, in order to try and explain why and how people dream. This can be quite a difficult concept to understand so make sure you read through each part thoroughly.

Activation synthesis

  Hobson and McCarley argue that dreams occur when the mind tries to make sense of the activity in the brain which is taking place whilst someone sleeps. They also believe that the brain activity that occurs (especially during REM sleep) serves some other purpose, such as restoration and protein synthesis.

The researchers point out that brain activity is present during REM sleep but all muscles are paralysed causing movement inhibition . As well as this, REM sleep means that the brain is not picking up sensory information, which they refer to as sensory blockade . Despite this, they argue that random messages are being sent in the brain and this is the ‘activation’ part of their theory.

These random thoughts are understood to come from neurons in the brain, which are activated and then fired – meaning that an electrical impulse occurs, causing neurochemicals to be released. As we saw in an earlier unit, this means that the neurochemicals will cross a synaptic gap and messages (which are ‘thoughts’ in this case) are sent.

Hobson and McCarley believe that these random thoughts are actually the basis of dreaming as several things come together (or are synthesised) in order to make this happen. The random thoughts, which are triggered by firing neurons, generate internal information. The brain then automatically tries to make sense of this information and this is when a person begins to dream, just as it would try to make sense of information in an environment when the person was awake.

Strengths of the activation-synthesis theory

• The evidence presented by Hobson and McCarley is compelling; when people sleep in a laboratory and are observed, REM sleep does appear to be a time when dreaming would occur as muscles and senses are not functioning and therefore the brain has to make sense of random information
• The theory has provided a basis for further investigation of the theory, which is ongoing even today.

Weaknesses of the activation-synthesis theory

• Other work in this area has been carried out on animals, which cannot be applied to human behaviour
• Some dreams appear to have specific meaning to the individual, which counteracts the idea that the thoughts that dreams are based on are completely random.

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ACTIVATION-SYNTHESIS HYPOTHESIS

speculation which points out dreams as being an output of cortical interpretation of haphazard energizing stemming from the underside of brain tissues by U.S. psychiatrists J. Allan Hobson (193.3- ) and Robert W. McCarleyl

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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

CC licensed content, Shared previously

• 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

All rights reserved content

• 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

General Psychology Copyright © by OpenStax and Lumen Learning is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Experimental Research on Dreaming: State of the Art and Neuropsychoanalytic Perspectives

Perrine m. ruby.

1 INSERM U1028, Lyon Neuroscience Research Center, Brain Dynamics and Cognition Team, Lyon, France

2 CNRS UMR5292, Lyon Neuroscience Research Center, Brain Dynamics and Cognition Team, Lyon, France

3 University Lyon 1, Lyon, France

Dreaming is still a mystery of human cognition, although it has been studied experimentally for more than a century. Experimental psychology first investigated dream content and frequency. The neuroscientific approach to dreaming arose at the end of the 1950s and soon proposed a physiological substrate of dreaming: rapid eye movement sleep. Fifty years later, this hypothesis was challenged because it could not explain all of the characteristics of dream reports. Therefore, the neurophysiological correlates of dreaming are still unclear, and many questions remain unresolved. Do the representations that constitute the dream emerge randomly from the brain, or do they surface according to certain parameters? Is the organization of the dream’s representations chaotic or is it determined by rules? Does dreaming have a meaning? What is/are the function(s) of dreaming? Psychoanalysis provides hypotheses to address these questions. Until now, these hypotheses have received minimal attention in cognitive neuroscience, but the recent development of neuropsychoanalysis brings new hopes of interaction between the two fields. Considering the psychoanalytical perspective in cognitive neuroscience would provide new directions and leads for dream research and would help to achieve a comprehensive understanding of dreaming. Notably, several subjective issues at the core of the psychoanalytic approach, such as the concept of personal meaning, the concept of unconscious episodic memory and the subject’s history, are not addressed or considered in cognitive neuroscience. This paper argues that the focus on singularity and personal meaning in psychoanalysis is needed to successfully address these issues in cognitive neuroscience and to progress in the understanding of dreaming and the psyche.

The word “dream” is commonly used to express an unattainable ideal or a very deep and strong desire:

I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin, but by the content of their character. Martin Luther King

In dream reports, however, one often notices banal situations, strange scenes, or even frightening events. Why is there such a contrast between the popular meaning of the word “dream” and the content of dream reports? Why are some dream scenes so bizarre? Are dreams built from images that arise randomly from the sleeping brain? Or is the emergence and organization of dream images controlled by currently unknown parameters? Does dreaming have a function?

Answering these questions is not easy because dreaming is elusive. We still do not know when it happens during the night, how long it lasts, whether we can recall its entire content, or how to control it. For more than a century, such limited understanding of dreaming has seriously hampered experimental investigations. Nonetheless, scientific research has managed to produce considerable information about the phenomenology and physiology of dreaming and has improved our understanding of this fascinating phenomenon.

Experimental Research on Dreaming

Dreaming and experimental psychology, dream content.

Dreaming was first investigated on an experimental level in the nineteenth century. Calkins ( 1893 ) published the first statistical results about dreaming and argued that some aspects of dream content could be quantified. Later, questionnaires and automatic analysis of the lexical content of dream reports allowed psychologists to show that dream content has some precise phenomenological characteristics. According to psychological studies (Hall and Van de Castle, 1966 ; Schwartz, 1999 ), visual imagery occurs more frequently in dreams than imagery of other senses (audition, olfaction, touch, and taste); the dream drama is mostly lived by the dreamer from a first-person perspective; some elements of real-life events previously experienced by the dreamer often contribute to the scene of the dream; most often, the dream sequence is not within the dreamer’s voluntary control (i.e., the dreamer may be convinced during the dream that the dream’s story is really happening); temporal and spatial incoherencies can occur in the dream story; the dream report is often full of people interacting with each other (e.g., discussions, fights, pursuit, sexuality); and finally, the dream report often contains strong emotions.

Substantial variability of content exists, however, among the same individual’s dreams and among the dreams of different individuals. Further, psychological studies have shown that many internal and external parameters can influence dream content. For example, males report more aggression and violence in their dreams than do females (Nielsen et al., 2003 ; Schredl et al., 2004 ). External stimulation perceived by the dreamer can be incorporated into dreams (Koulack, 1969 ; Saint-Denys, 1867; Hoelscher et al., 1981 ), as illustrated by the famous Dali painting Dream Caused by the Flight of a Bee around a Pomegranate a Second before Awakening . The current concerns of the subject may also be found in the content of his/her dreams (Schwartz, 1999 ; Domhoff and Schneider, 2008 ), and many aspects of the subject’s daily life were found to influence dream content, including news events (Bulkeley and Kahan, 2008 ), musical practice (Uga et al., 2006 ), religious beliefs (Domhoff and Schneider, 2008 ), chronic pain (Raymond et al., 2002 ), mood (Cartwright et al., 1998a ), or a violent living environment (Valli et al., 2005 ). By contrast, congenital or acquired malformations do not seem to significantly influence dream content (Voss et al., 2010 ; Saurat et al., 2011 ).

Based on these results, two opposing hypotheses were formulated: the continuity hypothesis (Schredl and Hofmann, 2003 ) and the discontinuity hypothesis (Rechtschaffen, 1978 ; Kahn et al., 1997 ; Stickgold et al., 2001 ). The former relies on results showing that the themes of an individual’s thoughts during waking life and dreaming are similar; the latter focuses on the fundamentally different structures of thoughts during waking life and dreaming. Voss et al. ( 2010 ) stressed in their recent paper that these hypotheses represent oversimplified approaches to dream analysis and argued that waking and dreaming thoughts were related but structurally independent; in other words, she argued in favor of merging the continuity and discontinuity hypotheses.

Dream report frequency

Dream report frequency (DRF) can vary within subjects and varies substantially among subjects. In a study of 900 German subjects with a large age range from various socioprofessional categories, the mean DRF was approximately 1 dream report per week (Schredl, 2008 ). This result shows that the dream experience is common and familiar to everyone. Psychological studies have demonstrated that many parameters covary with DRF and may thus influence it.

Sleep parameters

First, DRF varies according to the sleep stage preceding awakening (e.g., Dement and Kleitman, 1957b ; Nielsen, 2000 , for a review). More dream reports are obtained after an awakening during rapid eye movement (REM) sleep than after an awakening during non-REM (NREM) sleep. These results inspired the REM sleep hypothesis of dreaming (see the section Dreaming and Neuroscience). Second, DRF increases with the number of awakenings during sleep, according to retrospective self-evaluations of awakenings (Cory and Ormiston, 1975 ; Schredl et al., 2003 ). Such studies showed that the more the subjects tended to awaken during sleep, the higher their DRF. These results support the hypothesis of Koulack and Goodenough ( 1976 ), which proposes that nocturnal awakenings facilitate the encoding of the dream in memory and thus facilitate dream recall upon awakening. However, this hypothesis has not been tested by measuring awakenings with polysomnographic recordings in healthy subjects with various DRFs. Finally, DRF varies according to the method of awakening. Abrupt awakenings lead to more dream reports than gradual awakenings (Shapiro et al., 1963 , 1965 ; Goodenough et al., 1965 ).

Physiological and environmental parameters

Dream report frequency deceases with age (e.g., Schredl, 2008 ) and tends to be slightly higher among females than males (e.g., Schredl, 2008 ; Schredl and Reinhard, 2008 ). Remarkably, Schredl’s ( 2008 ) results revealed that DRF also varied according to the size of the subject’s place of residence.

Psychological parameters

First, increased professional stress or interpersonal stress resulted in an increase in DRF (for a review, see Schredl, 1999 ). Second, an interest in dreams or a positive attitude toward dreams clearly covaries with DRF (Hill et al., 1997 ; Schredl, 1999 ; Schredl et al., 2003 ). The greater an individual’s interest in dreams, the higher his/her DRF. Third, several cognitive abilities have been found to covary with DRF. Contradictory results have been reported for the correlation between DRF and memory abilities (short-term, long-term, visual, verbal, implicit, and explicit; significant positive correlation: Cory and Ormiston, 1975 ; Belicki et al., 1978 ; Butler and Watson, 1985 ; Schredl et al., 1995 ; Solms, 1997 ; no significant correlation: Cohen, 1971 ; Belicki et al., 1978 ; Schredl et al., 1995 , 1997 , 2003 ; Solms, 1997 ) and the correlation between DRF and visual imagery ( significant positive correlation : Hiscock and Cohen, 1973 ; Richardson, 1979 ; Okada et al., 2000 ; no significant correlation : Hill et al., 1997 ; Okada et al., 2000 ). However, several studies have consistently shown that DRF is positively correlated with creativity (Fitch and Armitage, 1989 ; Schredl, 1999 ; Schredl et al., 2003 ) and intelligence scales (multiple-choice vocabulary test, Schonbar, 1959 ; Shipley Intelligence Scale, Connor and Boblitt, 1970 ). Finally, many authors have reported a correlation between DRF and personality traits. Subjects with a high DRF are more likely to have a personality with thinner boundaries (Hartmann described people with thin boundaries as being open, trustworthy, vulnerable, and sensitive; Hartmann, 1989 ; Hartmann et al., 1991 ; Schredl et al., 2003 ), to be more anxious (Schonbar, 1959 ; Tart, 1962 ), to have a higher level of absorption (the absorption scale measures the capacity to become absorptively involved in imaginative and esthetic experiences; Hill et al., 1997 ; Schredl, 1999 ; Schredl et al., 2003 ), to be more open to experience (Hill et al., 1997 ; Schredl et al., 2003 ), and to be less alexithymic (alexithymia is a personality variable that incorporates difficulty identifying and describing feelings, difficulty distinguishing between feelings and the physical sensation of emotional arousal, limited imaginative processes, and an externally oriented cognitive style; De Gennaro et al., 2003 ; Nielsen et al., 2011 ) compared to subjects with a low dream recall frequency. However, those results have not always been reproducible (e.g., Schredl, 2002 for openness to experience; Cory and Ormiston, 1975 ; Hill et al., 1997 for anxiety; Nielsen et al., 1997 for alexithymia) and, according to the recent review by Blagrove and Pace-Schott ( 2010 ), it is difficult to draw conclusions about a possible link between personality traits and DRF.

In conclusion, numerous parameters have been identified that covary with DRF. Schredl stressed in many of his papers that the studied parameters usually explain only a small percentage of the total variance (e.g., Schredl, 2008 ). Thus, the DRF variation profile suggests that the production, encoding and recall of dreams are influenced by numerous parameters that probably interact with each other.

Dreaming and neuroscience

The neuroscientific approach to dreaming arose at the end of the 1950s with the discovery of REM during human sleep by the American physiologist Nathaniel Kleitman and his team (Aserinsky and Kleitman, 1953 ; Dement and Kleitman, 1957a ). During these sleep episodes with saccades, the researchers noticed a decrease in voltage and an increase in frequency in the EEG, accompanied by an increase in cardiac frequency variability and a decrease in body movements. They concluded that these physiological modifications indicate a particular sleep stage, which they called REM sleep. A few years later, the French team led by neurobiologist Michel Jouvet discovered that the lack of movement during REM sleep in cats was due to a general muscular atonia, controlled notably by the locus coeruleus α in the brainstem (Jouvet and Michel, 1959 ; Berger, 1961 later showed that muscular atonia during REM sleep also occurs in humans). Interestingly, the inability to move during REM sleep indicates deep sleep and paradoxically, the fast EEG activity of REM sleep resembles EEG activity in wakefulness. Jouvet concluded that this particular physiological state is associated with a “third state” of the brain (in addition to the brain states associated with wakefulness and NREM sleep) which he called “paradoxical sleep” instead of “REM sleep” (Jouvet et al., 1959 ; Jouvet, 1992 ). Several years later, Fisher et al. ( 1965 ) discovered another physiological characteristic of REM sleep: the penile erection.

During the same period, the American team noticed that a subject awakened during REM sleep very often reported a dream (80% of awakenings in REM sleep vs. 6% of awakenings in NREM sleep are followed by a dream report, according to Dement and Kleitman, 1957b ). Researchers concluded that dreaming occurs during REM sleep. The eye movements of REM sleep would allow the dreamer to scan the imaginary scene of the dream (the scanning hypothesis); the cerebral cortex activation revealed by the rapid EEG would allow intense cognitive activity, creating the complex stories of a dream; and the lack of muscle tone would prevent the dreamer from acting out his dreams. From that time on, researchers investigated REM sleep to obtain answers about dreaming.

In the 1990s, researchers used functional neuroimaging techniques such as positron emission tomography (PET) to investigate brain activity during REM sleep in humans. This new approach enabled researchers to demonstrate that the functional organization of the brain during REM sleep is different from the functional organization of the brain during wakefulness (Maquet et al., 1996 ; Braun et al., 1998 ). In comparison to wakefulness, brain activity during REM sleep is decreased in some brain regions (e.g., in the dorsolateral prefrontal cortex; Braun et al., 1998 ) and increased in other regions (e.g., in the occipital and temporal cortex, the hippocampus and parahippocampus, the anterior cingulate, the precentral and postcentral gyri, the superior parietal cortex, and the pons; Braun et al., 1998 ; Maquet et al., 2000 ). Looking more generally for brain activity correlating with REM sleep (the vigilance states considered included wakefulness, slow-wave sleep, and REM sleep), Maquet et al. ( 1996 ) found negative correlations in the precuneus, posterior cingulate cortex, temporoparietal junction, and dorsolateral prefrontal cortex and positive correlations in the amygdala, anterior cingulate, postcentral gyrus, thalamus, and pons (see Schwartz and Maquet, 2002 ; Maquet et al., 2005 ; Nir and Tononi, 2010 for reviews). Based on these results, researchers argued that the particular functional organization of the brain during REM sleep could explain the phenomenological characteristics of dream reports (Hobson and Pace-Schott, 2002 ; Schwartz and Maquet, 2002 ; Maquet et al., 2005 ; Nir and Tononi, 2010 ). They considered that brain activity increases and decreases during REM sleep could be interpreted on the basis of what we know about brain activity during wakefulness. In this context, the increased occipital cortex activity during REM sleep could explain the visual component of dream reports because neuroimaging results during wakefulness showed that visual imagery with the eyes closed activates the occipital cortex (Kosslyn and Thompson, 2003 ). The decreased activity in the temporoparietal junction during REM sleep may explain why dreams are mainly experienced in the egocentric coordinates of the first-person; indeed, during wakefulness, activity in the temporoparietal junction was reported to be greater for allocentric vs. egocentric representation (e.g., Ruby and Decety, 2001 ; Zacks et al., 2003 ) and for third- vs. first-person perspective (e.g., Ruby and Decety, 2003 , 2004 ). The increased activity in the hippocampus during REM sleep could explain why dreams are often composed of known images or characters, as the hippocampus is known to be associated with the encoding and retrieval of lived events during wakefulness (e.g., Piolino et al., 2009 ). The decreased activity in the lateral prefrontal cortex during REM sleep could explain why dream stories lack consistency, why the dreamer’s perception of time is altered, why the dream story is beyond the control of the dreamer and why the dreamer is convinced that the dream story is really happening. Indeed, during wakefulness, the lateral prefrontal cortex is involved in executive function, cognitive control, and working memory (Petrides, 2005 ; Koechlin and Hyafil, 2007 ). The increased activity in the medial prefrontal cortex during REM sleep could explain the attribution of thoughts, beliefs, and emotions to the characters in the dream because, during wakefulness, the medial prefrontal cortex is known to participate in mind reading (Ruby et al., 2007 , 2009 ; Legrand and Ruby, 2009 ). The increased activity in the motor cortex (precentral gyrus) during REM sleep could explain the movements of the characters’ bodies in the dream because, during wakefulness, motor imagery, and the imagination of someone’s action from the third-person perspective involve the precentral gyrus (Decety et al., 1994 ; Ruby and Decety, 2001 ). Finally, the amygdala’s activity during REM sleep could explain why emotions, especially fear, are often mentioned in dream reports; indeed, the amygdala is involved in the processing of emotional stimuli during wakefulness (Adolphs, 2008 ).

In conclusion, results from experimental psychology and neuroscience allow us to better understand the phenomenology of dreaming and the cerebral correlates of some characteristics of dream reports. Still, what do they tell us about the role of dreaming? What are the current hypotheses about dream function(s)?

Hypotheses about dream function(s)

No function.

At the end of the twentieth century, the neurologist Alan Hobson, who was profoundly anti-psychoanalysis, proposed a theory that deprived dreaming of any function. Hobson argued that dreaming is an epiphenomenon of REM sleep: “Because dreams are so difficult to remember, it seems unlikely that attention to their content could afford much in the way of high-priority survival value. Indeed, it might instead be assumed that dreaming is an epiphenomenon of REM sleep whose cognitive content is so ambiguous as to invite misleading or even erroneous interpretation” (Hobson et al., 1998 ).

Psychological individualism

In contrast, other teams, like Michel Jouvet’s, believed that dreaming serves a vital function. In 1979, Jouvet’s team blocked muscular atonia during REM sleep in a cat by damaging the locus coeruleus α in its brainstem. This lesion resulted in the appearance of movements during REM sleep. Movies from the Jouvet lab show sleeping cats performing complex motor actions (with altered control and coordination) resembling those of wakefulness, such as fur licking, growling, chasing prey, mastication, and fighting. From these videos, the authors concluded that the cat was acting out its dream, and they called this non-physiological state “oneiric behavior” (Sastre and Jouvet, 1979 ). These results led Jouvet to propose that dreaming plays a role in reinforcing a species’ typical behavior. Later in his career, Jouvet moved toward a hypothesis focusing on the role of dreaming in the individual dimension. He speculated that dreams (note that, for Jouvet, dreams and paradoxical sleep were equivalent) could be involved in psychological individualism and in the stability of the dreamer’s personality (Jouvet, 1991 , 1992 , 1998 ). According to Jouvet, “the brain is the sole organ of homeotherms that do not undergo cell division. We thus have to explain how certain aspects of psychological heredity (found in homozygote twins raised in different surroundings) may persist for a whole life (psychological individuation). A definitive genetic programming during development (by neurogenesis) is unlikely due to the plasticity of the nervous system. That is why we have to consider the possibility of an iterative genetic programming. The internal mechanisms (synchronous) of paradoxical sleep (SP) are particularly adapted to such programming. This would activate an endogenous system of stimulation that would stimulate and stabilize receptors genetically programmed by DNA in some neuronal circuits. The excitation of these neurons during SP leads to oniric behaviors that could be experimentally revealed – the lists of these behaviors are specific to each individual and indirect data suggest a genetic component of this programming. Amongst the mechanisms allowing the iterative programming of SP, sleep is particularly important. Security – and hence the inhibition of the arousal system – is a sine qua non-condition for genetic programming to take place. In that sense, sleep could very well be the guardian of dreaming” (Jouvet, 1991 ). In other words, Jouvet’s hypothesis is that paradoxical sleep restores neuronal circuitry that was modified during the day to preserve the expression of the genetic program that codes for psychological characteristics. This process would ensure the stability of personality across time.

The threat simulation theory

The Finnish psychologist Antti Revonsuo recently proposed a hypothesis called threat simulation theory, which explains the fearful characteristics of dream content (Revonsuo, 2000 ; Valli and Revonsuo, 2009 ). According to this theory, dreams serve as virtual training places to improve threat avoidance or threat fighting ability. The theory postulates that such nocturnal training makes the dreamer more efficient at resolving threatening situations during wakefulness.

Emotional regulation

Cartwright et al. ( 1998a , b ) defended the idea that dreaming is involved in emotional regulation. Her team showed that, in healthy subjects, the depression level before sleep was significantly correlated with affect in the first REM report. Her team also observed that low scorers on the depression scale displayed a flat distribution of positive and negative affect in dreams, whereas those with a depressed mood before sleep showed a pattern of decreasing negative and increasing positive affect in dreams reported from successive REM periods (Cartwright et al., 1998a ). These results led Cartwright’s team to suggest that dreaming may actively moderate mood overnight in normal subjects. The team strengthened this hypothesis by showing that among subjects who were depressed because of a divorce, those who reported more negative dreams at the beginning of sleep and fewer at the night’s end were more likely to be in remission 1 year later than subjects who had fewer negative dreams at the beginning of sleep and more at the end of the night (Cartwright et al., 1998b ). The researchers concluded that negative dreams early in the night may reflect a within-sleep mood regulation process, whereas those that occur later may indicate a failure in the completion of this process.

Memory consolidation

Finally, a current mainstream hypothesis in cognitive neuroscience credits sleep and dreaming with a role in memory consolidation (for a recent review, see Diekelmann and Born, 2010 ). Numerous studies have shown that brain activity during training is replayed during post-training sleep (e.g., using a serial reaction time task Maquet et al., 2000 , demonstrated replay during REM sleep; using a maze exploration task Peigneux et al., 2004 , demonstrated replay during slow-wave sleep). Decreased performance during the post-training day in sleep-deprived subjects further suggested that the replay of brain activity at night contributes to memory consolidation (e.g., Maquet et al., 2003 ). Only recently, however, have experimental results in humans argued in favor of a role of dreaming per se in memory consolidation. In one study, subjects were trained on a virtual navigation task before taking a nap. Post-nap tests showed that subjects who dreamed about the task performed better than subjects who did not dream (note that only 4 out of 50 subjects dreamed about the task in this study; Wamsley et al., 2010 ). Using a different approach, Nielsen and colleagues provided additional arguments supporting a link between dreams and memory (Nielsen et al., 2004 ; Nielsen and Stenstrom, 2005 ). This team demonstrated that dreams preferably incorporate events that the dreamer lived the day before and events that the dreamer lived 7 days before the dream (U shaped curve). Animal studies have shown that after associative learning, the excitability of hippocampal cells increases (which leads to an increase in neuronal plasticity) and then returns to baseline 7 days after training (Thompson et al., 1996 ). The similarity between the delay of episodic event incorporation into dreams and the delay of post-training cellular plasticity in the hippocampus led the Canadian team to suggest a link between dreaming and episodic memory consolidation.

In summary, the preceding section describes the current state of the art on dreaming, its phenomenology and cerebral correlates and hypotheses about its functions. Some substantial advances have been made, but much remains to be understood.

Unresolved Issues

The link between oneiric behaviors and dream reports.

A piece of evidence in favor of a strong link between REM sleep and dreaming is the oneiric behavior (the appearance of complex motor behaviors when motor inhibition is suppressed during REM sleep) discovered by Sastre and Jouvet ( 1979 ) in cats and reproduced by Sanford et al. ( 2001 ) in rats. Researchers interpreted these results as the animal acting out its dream. However, as animals do not talk, the link between oneiric behavior and dream recall cannot be tested experimentally. This limitation seriously hampers our understanding of dreaming. In humans, complex motor behaviors (e.g., talking, grabbing, and manipulating imaginary objects, walking, and running) can also occur during REM sleep in a pathological context. This syndrome is called REM sleep behavior disorder (RBD). It can be caused by substance withdrawal (e.g., alcohol, Nitrazepam) or intoxication (e.g., caffeine, tricyclic antidepressants) or by various diseases (e.g., Parkinson’s and Alzheimer’s diseases, pontine neoplasms). According to physicians experts on this syndrome, some patients report dreams that are consistent with their behaviors in REM sleep (Mahowald and Schenck, 2000 ). According to the literature, however, such matches seem to be loose and not systematic. Only one study has tested whether observers can link dream content to sleep behaviors in RBD (Valli et al., 2011 ). In this study, each video recording of motor manifestations was combined with four dream reports, and seven judges had to match the video clip with the correctly reported dream content. The authors found that reported dream content can be linked to motor behaviors at a level better than chance. However, only 39.5% of video-dream pairs were correctly identified. Note, however, that because the authors obtained only movements and not behavioral episodes for many RBD patients, the link between videos and dream reports was unfairly difficult to make.

It is important to note that motor behavior during sleep can happen outside of REM sleep. Sleepwalking and sleep terrors, which occur during NREM sleep, are usually not considered dream enactments. However, we know that dreams can happen during NREM sleep, and many patients report dreamlike mentation after awakening from sleepwalking or sleep terrors (71%, according to Oudiette et al., 2009 ). In addition, Oudiette et al. ( 2009 ) reported that the dreamlike mentation can correspond with the sleep behavior in NREM sleep. Consequently, the authors concluded that sleepwalking may represent an acting out of corresponding dreamlike mentation.

Recent research suggests that any kind of motor behavior during sleep can be considered an oneiric behavior. One of the challenges for future research is to test the strength of the link between these oneiric behaviors and dream reports in a controlled and systematic way.

Neurophysiological correlates of dreaming

Despite the numerous neuroimaging studies of sleep in humans, the neurophysiological correlates of dreaming remain unclear.

Indeed, dreaming can happen during NREM sleep, and although NREM brain activity differs substantially from REM sleep brain activity (Maquet et al., 2000 ; Buchsbaum et al., 2001 ), some NREM dreams are phenomenologically indistinguishable from REM dreams (Hobson, 1988 ; Cavallero et al., 1992 ; Cicogna et al., 1998 ; Wittmann et al., 2004 ). This phenomenon is difficult to understand given what we currently know about the sleeping brain and about dreaming. One explanation may rely on the possibility that brain activity during sleep is not as stable as we think.

Brain activity during REM sleep in humans is considered to be well understood (Hobson and Pace-Schott, 2002 ; Schwartz and Maquet, 2002 ; Nir and Tononi, 2010 ), but several results question this notion. First, contrary to the common belief that dorsolateral prefrontal cortex activity decreases during REM sleep, several studies have reported increased activity in the dorsolateral prefrontal cortex during REM sleep (Hong et al., 1995 , 2009 ; Nofzinger et al., 1997 ; Kubota et al., 2011 ). Second, brain activity during REM sleep is heterogeneous. The mean regional cerebral blood flow during 1 min of REM sleep (e.g., as reported in Maquet et al., 1996 ) and the regional cerebral blood flow associated with the rapid eye movements of REM sleep (Hong et al., 2009 ; Miyauchi et al., 2009 ) highlight different brain regions. Finally, few congruencies have been noted in the results of studies investigating brain activity during REM sleep (Hong et al., 1995 , 2009 ; Maquet et al., 1996 , 2000 ; Braun et al., 1997 , 1998 ; Nofzinger et al., 1997 ; Peigneux et al., 2001 ; Wehrle et al., 2005 ; Miyauchi et al., 2009 ; Kubota et al., 2011 ), even between studies using the same technique and the same contrasts (e.g., Braun et al., 1998 ; Maquet et al., 2000 ), or between studies investigating the same REM event (e.g., brain activity associated with rapid eyes movements, as in Peigneux et al., 2001 ; Wehrle et al., 2005 ; Hong et al., 2009 ; Miyauchi et al., 2009 ). Furthermore, few brain regions are consistently reported across the majority of the studies. This inconsistency suggests great intra- and intersubject variability in brain activity during REM sleep in humans. A challenge for future research will be to find out whether the variability in brain activity during REM sleep can be explained by the variability in dream content.

Because dream reports can be collected after awakenings from any sleep stage, one may hypothesize that the brain activity that subserves dreaming (if such brain activity is reproducible across dreams) is quite constant throughout the night and can be observed during all sleep stages. Some results have supported this hypothesis and encouraged further attention in this direction. Buchsbaum et al. ( 2001 ), for example, reported that metabolism in the primary visual areas and certain parts of the lateral temporal cortex does not fluctuate much across REM and slow-wave sleep. Similarly, Nielsen’s team found that dream recall (vs. no dream recall) was associated with decreased alpha (8–12 Hz) power in the EEG preceding awakening, regardless of the sleep stage (Stage 2 or REM sleep; Esposito et al., 2004 ). Interestingly, some authors have suggested that decreased power in the alpha band during wakefulness reflects search and retrieval processes in long-term memory (for a review, see Klimesch, 1999 ).

Processes of selection and organization of dream representations

Nielsen’s team found that episodic events from the 1, 7, and 8 days before a dream were more often incorporated into the dream than were events from 2 or 6 days before the dream (Nielsen et al., 2004 ; results reproduced by Blagrove et al., 2011 ). This result tells us that internal processes control and shape dream content and thus help us to constrain and shape hypotheses about the function and biological basis of dreaming.

At the end of the nineteenth century, Saint-Denys (1867) showed that a sensory stimulus (e.g., the scent of lavender) presented to a sleeping subject without his or her knowledge could induce the incorporation of an event associated with the stimulus (e.g., holidays spent near a lavender field) into the dream, regardless of the delay between the dream and the association stimulus/events (lavender scent/holidays). The author demonstrated that the external world can influence dream content in a direct or indirect way.

Finally, it appears that both external and internal parameters can shape or govern dream content. Nonetheless, few of these parameters are known, and some regularities in the phenomenology of dreams suggest that more influencing parameters remain to be discovered. For example, some individuals experience recurring themes, characters, or places in their dreams. In line with this observation, Michael Schredl’s team showed that the content and style of a person’s life strongly influence dream content (Schredl and Hofmann, 2003 ). However, the rule(s) governing which lived events are incorporated into dreams remain unknown. Do the representations constituting the dream emerge randomly from the brain, or do they surface according to certain parameters? Similarly, is the organization of the dream’s representations chaotic, or is it determined by rules? Does dreaming have a meaning? What is/are the function(s) of dreaming?

Dreaming, Psychoanalysis, and Neuropsychoanalysis

Psychoanalysis, which was developed by the neurologist Sigmund Freud in the beginning of the twentieth century, proposes answers to the questions raised above. Indeed, his theory of the human mind comprises hypotheses about the rules of selection and organization of the representations that constitute dreams.

At the beginning of the twentieth century, Freud presented the concept of the unconscious. He proposed that a part of our mind is made up of thoughts, desires, emotions, and knowledge that we are not aware of, but that nevertheless profoundly influence and guide our behaviors. In his books (e.g., Freud, 1900, 1920 ), Freud proposes that the unconscious mind comes out in slips and dreams. Its expression, however, is coded within dreams (the work of dream), and unconscious thoughts are distorted before they emerge in the conscious mind of the sleeping subject (manifest content of the dream). As a consequence, the dreamer is not disturbed by repressed and unacceptable thoughts (latent content of the dream) and can continue sleeping (this is the reason why Freud considered dreams the guardians of sleep). Hence, according to Freud, decoding dreams’ latent content provides an access to the unconscious mind.

In Freud’s theory of the mind, unconscious thoughts and feelings may cause the patient to experience life difficulties and/or maladjustment, and free unconscious thoughts can help the patient gain insight into his/her situation. As a consequence, Freud developed techniques to decode dreams and provide a way for an analyst to look inside the words and unconscious images of the patient, and to free them through patient insight. One of these techniques is called free association, and is regarded as an essential part of the psychoanalytic therapy process. In order for an analyst to get to the latent content of a dream, he requires the patient to discuss the dream’s manifest content and encourage free association about the dream. Free association is the principle that the patient is to say anything and everything that comes to mind. This includes decensoring his/her own speech so that he/she truly expresses everything. Over time, the therapist or analyst will draw associations between the many trains of uncensored speech the patient shares during each session. This can lead to patient insight into their unconscious thoughts or repressed memories, and the accomplishment of their ultimate goal of “freedom from the oppression of the unconscious” (Trull, 2005 ).

Hence, Freud considered that dreams, as well as slips, have a meaning and can be interpreted, so that one is justified in inferring from them the presence of restrained or repressed intentions (Freud, 1900, 1920 ). Note that, in Freud’s theory of the mind, the words “meaning” and “intention” are closely linked: “Let us agree once more on what we understand by the ‘meaning’ of a psychic process. A psychic process is nothing more than the purpose which it serves and the position which it holds in a psychic sequence. We can also substitute the word ‘purpose’ or ‘intention’ for ‘meaning’ in most of our investigations” (Freud, 1920 ).

In other words, according to Freud, decoding dreams with the free association method provides an access to what makes each of us so special, uncorvering the forces that guide one’s behavior. It gives access to an unknown dimension of ourselves that is fundamental in understanding who we are. It provides access to personal meaning.

This hypothesis, attributing significant importance and meaning to dreams, has rarely been considered by neuroscientists who often consider Freud’s work and theory unscientific.

However, this situation may change as the relationship between psychoanalysis and neuroscience evolves. The starting point was the creation of the International Society for Neuropsychoanalysis in 2000. It was founded by neuropsychologist and psychoanalyst Mark Solms with the intention to promote interactions and collaborations between psychoanalysis and neuroscience. The challenge was serious, as illustrated by neuroscientist Alan Hobson’s aggressiveness in the famous dream debate (Alan Hobson vs. Mark Solms) entitled “Should Freud’s dream theory be abandoned?” held in Tucson, Arizona, in 2006 during the Towards a Science of Consciousness meeting (scientific arguments can be found in Solms, 2000 and Hobson et al., 2000 ). Alan Hobson tried to convince the assembly that Freud was 100% wrong and that Freud’s dream theory was misguided and misleading and should be abandoned. He aimed to demonstrate that Freud’s dream theory is incompatible with what we know about how the brain works. He added that Freud’s dream theory was not scientific because it was not testable or falsifiable. Finally, he presented his model of dreaming, the activation-synthesis hypothesis (Hobson and McCarley, 1977 ; Hobson et al., 2000 ): “The Activation-Synthesis model of dream construction proposed that the phasic signals arising in the pontine brainstem during REM sleep and impinging upon the cortex and limbic forebrain led directly to the visual and motor hallucinations, emotion, and distinctively bizarre cognition that characterize dream mentation. In doing so, these chaotically generated signals arising from the brain stem acted as a physiological Rorschach test, initiating a process of image and narrative synthesis involving associative and language regions of the brain and resulting in the construction of the dream scenarios.” In contrast, Mark Solms demonstrated that what is currently known about the dreaming brain is at least broadly consistent with Freud’s dream theory. He argued that it is generally accepted that brain stem activation is necessary, but not sufficient, to explain the particular characteristics of dream consciousness. What does explain the particular characteristics of dream consciousness, according to Solms, are the following features of brain activity during REM sleep (Braun et al., 1997 ): the activation of core forebrain emotion and instinctual drive mechanisms, i.e., the limbic and paralimbic brain areas (the anterior cingulate, insula, hippocampus, parahippocampal gyrus, and temporal pole), and of the posterior perceptual system (the fusiform gyrus, superior, inferior and middle temporal gyrus, and angular gyrus) and the deactivation of executive dorsolateral frontal control mechanisms (the dorsolateral prefrontal cortex). He further argued that his lesion studies (Solms, 1997 ) are congruent with neuroimaging results because they showed that a total cessation of dreaming results from lesions in the medial part of the frontal lobe and in the temporoparietal junction (whereas no cessation of dreaming was observed for core brainstem lesions or for dorsolateral prefrontal lesions). Finally he emphasized that the activation of motivational mechanisms (such as drives and basic emotions) and of posterior perceptual system associated with deactivation of the executive control (i.e., reality oriented regulatory mechanism) during REM sleep, is broadly consistent with Freud’s dream theory which claims that our instinctual drive states (notably appetitive and libidinal drive system) are relatively disinhibited during sleep. Note that experimental results demonstrating the existence of unconscious representations that guide behavior (e.g., Shevrin and Fritzler, 1968 ; Bunce et al., 1999 ; Arminjon, 2011 , for a review) could also have been cited in support of Freud’s dream theory. This debate was a success for Mark Solms and neuropsychoanalysis. Indeed, at the end of the debate, approximately 100 people voted “no” (i.e., “Freud’s dream theory should not be abandoned”), approximately 50 people voted “yes” and 50 voted “I don’t know”.

Solms’ ( 1997 , 2000 ) approach to dreaming and his experimental results fundamentally challenged our current understanding of dreaming. He proposes that dreaming and REM sleep are controlled by different brain mechanisms. According to Solms, REM sleep is controlled by cholinergic brain stem mechanisms, whereas dreaming is mediated by forebrain mechanisms that are probably dopaminergic. This implies that dreaming can be activated by a variety of NREM triggers. Several experimental results support this hypothesis.

First, behavioral studies have demonstrated that the link between REM sleep and dream reports is lax. Subjects awakened during NREM sleep can recall dreams at a high rate (Foulkes, 1962 : 74% of awakenings in NREM sleep were followed by dream reports; Cavallero et al., 1992 : 64%; Wittmann et al., 2004 : 60%); dreams can be recalled after a nap consisting only of NREM sleep (Salzarulo, 1971 ; Palagini et al., 2004 ); and some individuals never recall dreams, even when awakened from REM sleep (Pagel, 2003 ). In addition, in healthy subjects with a normal dream recall frequency (around 1 dream recall per week, Schredl, 2008 ), dream recall after an awakening during REM sleep is not systematic: 5–30% of awakenings in REM sleep are not followed by a dream recall, according to the literature (e.g., Dement and Kleitman, 1957a , b ; Foulkes, 1962 ; Hobson, 1988 ). Finally, 5–10% of NREM dreams cannot be distinguished from REM dreams based on their content (Hobson, 1988 ; Cavallero et al., 1992 ; Cicogna et al., 1998 ; Wittmann et al., 2004 ).

Second, as Solms ( 2000 ) argued, the amount of dream recall can be modulated by dopamine agonists (Scharf et al., 1978 ; Nausieda et al., 1982 ) without concomitant modification of the duration and frequency of REM sleep (Hartmann et al., 1980 ). Dream recall can be suppressed by focal brain lesions (at the temporo-parieto-occipital junction and ventromedial prefrontal cortex; Solms, 1997 , 2000 ). These lesions do not have any appreciable effects on REM frequency, duration, or density (Kerr et al., 1978 ; Michel and Sieroff, 1981 ). Finally, some clinical studies suggest that a dream can be triggered by nocturnal seizures in NREM sleep, i.e., by focal brain stimulation. Some cases of recurring nightmares caused by epileptiform activity in the temporal lobe have indeed been reported (Solms, 2000 ).

Conclusion: Collaboration between Neuroscience and Psychoanalysis Would Benefit Dream Research

Considering the issues that remain unresolved (e.g., neurophysiologic variability, parameter(s) influencing the emergence of representations in dreams, the meaning of dreams), a psychoanalytic perspective would certainly benefit dream research by providing new directions/leads and helping to reach a comprehensive understanding of dreaming.

On the one hand, psychological research has demonstrated that dream content is influenced by one’s personal life, especially personal concerns (Schwartz, 1999 ; Schwartz and Maquet, 2002 ; Schredl and Hofmann, 2003 ), and some neuroscientists have hypothesized that dreaming is involved in psychological individualism. Thus, both psychology and neuroscience have provided results and hypotheses that validate the possibility that dreaming has something to do with personal and meaningful issues. On the other hand, Freud argued that the unconscious, which guides behaviors and desires, express itself during dreams. The two disciplines’ (cognitive neuroscience and psychoanalysis) convergence on dreaming thus seems obvious; however, very little collaboration has occurred to date.

Note that some experimental studies in psychology have considered the psychoanalytic perspective. For example, Greenberg et al. ( 1992 ) attempted “a research-based reconsideration of the psychoanalytical theory of dreaming.” They evaluated the presence of problems (defined as an expression of negative feeling or any situation evoking such feeling or requiring some change or adaptation) during dreaming and pre- and post-sleep wakefulness in two subjects. They showed that problems occurred very frequently in the manifest dream content and that these problems were nearly systematically related to the problems noted during pre-sleep wakefulness. In addition, they observed that effective dreams (i.e., dreams that presented some solution to the individuals’ problems) were followed by a waking state in which the impact of the problems was diminished, whereas ineffective dreams were followed by the persistence of the problems. This study thus confirmed that personal concerns influence dream content. In addition it provided new results suggesting that dreaming may have some psychological problem-solving function (this result recalls the neuroscientific findings that sleep has a cognitive problem-solving function associated with brain reorganization; e.g., Wagner et al., 2004 ; Darsaud et al., 2011 ). Greenberg et al.’s ( 1992 ) study managed to quantify personal issues and clearly broadened the cognitive neuroscience perspective on dreaming. To proceed further, approaches integrating psychoanalysis and neuroscience must now be developed. Several subjective issues at the core of the psychoanalytic approach, such as the concept of personal meaning, the concept of unconscious episodic memory and the subject’s history, are not addressed or considered in cognitive neuroscience. This limitation hampers the understanding of psychological and neurophysiological functioning in humans. These issues must be addressed, and the expertise of psychoanalysts in singularity and personal meaning is needed to do so in neuroscience and to further the understanding of dreaming and of the psyche.

Conflict of Interest Statement

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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The activation-synthesis hypothesis of dreams: a theoretical note

The author examines Hobson and McCarley's activation-synthesis hypothesis of dreams from the point of view of theory construction and the logic of science. After reviewing pertinent literature, he concludes that modern sciences has not yet established a well-defined mind-body isomorphism. Therefore, conclusions about the psychological meaning and motive of dreams cannot validly be drawn from neurobiological data.

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Why Do We Dream?

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

Dr. Sabrina Romanoff, PsyD, is a licensed clinical psychologist and a professor at Yeshiva University’s clinical psychology doctoral program.

Verywell / Madelyn Goodnight

What Is a Dream?

The role of dreams.

• Reflect the Unconscious
• Process Information
• Aid In Memory
• Spur Creativity
• Reflect Your Life
• Prepare and Protect
• Process Emotions
• Other Theories

Lucid Dreaming

Stress dreams.

Despite scientific inquiry, we still don't have a solid answer for why people dream. Some of the most notable theories are that dreaming helps us process memories and better understand our emotions , also providing a way to express what we want or to practice facing our challenges.

7 Theories on Why We Dream

A dream includes the images, thoughts, and emotions that are experienced during sleep. Dreams can range from extraordinarily intense or emotional to very vague, fleeting, confusing, or even boring. Some dreams are joyful, while others are frightening or sad. Sometimes dreams seem to have a clear narrative, while many others appear to make no sense at all.

There are many unknowns about dreaming and sleep, but what scientists do know is that just about everyone dreams every time they sleep, for a total of around two hours per night, whether they remember it upon waking or not .

Beyond what's in a particular dream, there is the question of why we dream at all. Below, we detail the most prominent theories on the purpose of dreaming and how these explanations can be applied to specific dreams.

How Do Scientists Study Dreams?

The question of why we dream has fascinated philosophers and scientists for thousands of years. Traditionally, dream content is measured by the subjective recollections of the dreamer upon waking. However, observation is also accomplished through objective evaluation in a lab.

In one study, researchers even created a rudimentary dream content map that was able to track what people dreamed about in real time using magnetic resonance imaging (MRI) patterns. The map was then backed up by the dreamers' reports upon waking.

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. Additionally, while many researchers believe that dreaming is essential to mental, emotional, and physical well-being, some scientists suggest that dreams serve no real purpose at all.

The bottom line is, while many theories have been proposed, no single consensus has emerged on why we dream.

Dreaming during different phases of sleep may also serve unique purposes. The most vivid dreams happen during rapid eye movement (REM) sleep , and these are the dreams that we're most likely to recall. We also dream during non-rapid eye movement (non-REM) sleep, but those dreams are known to be remembered less often and have more mundane content.

Dreams May Reflect the Unconscious

Sigmund Freud’s theory of dreams suggests that dreams represent  unconscious desires, thoughts, wish fulfillment, and motivations. According to Freud, people are driven by repressed and unconscious longings, such as aggressive and sexual instincts .

While many of Freud's assertions have been debunked, research suggests there is a dream rebound effect, also known as dream rebound theory, in which suppression of a thought tends to result in dreaming about it.

What Causes Dreams to Happen?

In " The Interpretation of Dreams ," Freud wrote that dreams are "disguised fulfillments of repressed wishes." He also described two different components of dreams: manifest content (actual images) and latent content (hidden meaning).

Freud’s theory contributed to the rise and popularity of dream interpretation . While research has failed to demonstrate that the manifest content disguises the psychological significance of a dream, some experts believe that dreams play an important role in processing emotions and stressful experiences.

Dreams Process Information

According to the activation-synthesis model of dreaming , which was first proposed by J. Allan Hobson and Robert McCarley, circuits in the brain become activated during REM sleep, which triggers the amygdala and hippocampus to create an array of electrical impulses. This results in a compilation of random thoughts, images, and memories that appear while dreaming.

When we wake, our active minds pull together the various images and memory fragments of the dream to create a cohesive narrative.  

In the activation-synthesis hypothesis, dreams are a compilation of randomness that appear to the sleeping mind and are brought together in a meaningful way when we wake. In this sense, dreams may provoke the dreamer to make new connections, inspire useful ideas, or have creative epiphanies in their waking lives.

Dreams Aid In Memory

According to the information-processing theory, sleep allows us to consolidate and process all of the information and memories that we have collected during the previous day. Some dream experts suggest that dreaming is a byproduct, or even an active part, of this experience processing.  

This model, known as the self-organization theory of dreaming , explains that dreaming is a side effect of brain neural activity as memories are consolidated during sleep. During this process of unconscious information redistribution, it is suggested that memories are either strengthened or weakened. According to the self-organization theory of dreaming, while we dream, helpful memories are made stronger, while less useful ones fade away.

Research supports this theory, finding improvement in complex tasks when a person dreams about doing them. Studies also show that during REM sleep, low-frequency theta waves were more active in the frontal lobe, just like they are when people are learning, storing, and remembering information when awake.

Dreams Spur Creativity

Another theory about dreams says that their purpose is to help us solve problems. In this creativity theory of dreaming, the unconstrained, unconscious mind is free to wander its limitless potential while unburdened by the often stifling realities of the conscious world. In fact, research has shown dreaming to be an effective promoter of creative thinking.

Scientific research and anecdotal evidence back up the fact that many people do successfully mine their dreams for inspiration and credit their dreams for their big "aha" moments.

The ability to make unexpected connections between memories and ideas that appear in your dreams often proves to be an especially fertile ground for creativity.

Dreams Reflect Your Life

Under the continuity hypothesis, dreams function as a reflection of a person's real life, incorporating conscious experiences into their dreams. Rather than a straightforward replay of waking life, dreams show up as a patchwork of memory fragments.

Still, studies show that non-REM sleep may be more involved with declarative memory (the more routine stuff), while REM dreams include more emotional and instructive memories. In general, REM dreams tend to be easier to recall compared to non-REM dreams.

Under the continuity hypothesis, memories may be fragmented purposefully in our dreams as part of incorporating new learning and experiences into long-term memory . Still, there are many unanswered questions as to why some aspects of memories are featured more or less prominently in our dreams.

Dreams Prepare and Protect

The primitive instinct rehearsal and adaptive strategy theories of dreaming propose that we dream to better prepare ourselves to confront dangers in the real world. The dream as a social simulation function or threat simulation provides the dreamer a safe environment to practice important survival skills.

While dreaming, we hone our fight-or-flight instincts and build mental capability for handling threatening scenarios. Under the threat simulation theory, our sleeping brains focus on the fight-or-flight mechanism to prep us for life-threatening and/or emotionally intense scenarios including:

• Running away from a pursuer
• Falling over a cliff
• Showing up somewhere naked
• Going to the bathroom in public
• Forgetting to study for a final exam

This theory suggests that practicing or rehearsing these skills in our dreams gives us an evolutionary advantage in that we can better cope with or avoid threatening scenarios in the real world. This helps explain why so many dreams contain scary, dramatic, or intense content.

Dreams Help Process Emotions

The emotional regulation dream theory says that the function of dreams is to help us process and cope with our emotions or trauma in the safe space of slumber.

Research shows that the amygdala, which is involved in processing emotions, and the hippocampus, which plays a vital role in condensing information and moving it from short-term to long-term memory storage, are active during vivid, intense dreaming. This illustrates a strong link between dreaming, memory storage, and emotional processing.

This theory suggests that REM sleep plays a vital role in emotional brain regulation. It also helps explain why so many dreams are emotionally vivid and why emotional or traumatic experiences tend to show up on repeat. Research has shown a connection between the ability to process emotions and the amount of REM sleep a person gets.

Content similarities and common dreams shared among dreamers may help promote connection. Research also notes heightened empathy among people who share their dreams with others, pointing to another way dreams can help us cope by promoting community and interpersonal support.

Other Theories About Why We Dream

Many other theories have been suggested to account for why we dream.

• One theory contends that dreams are the result of our brains trying to interpret external stimuli (such as a dog's bark, music, or a baby's cry) during sleep.
• Another theory uses a computer metaphor to account for dreams, noting that dreams serve to "clean up" clutter from the mind, refreshing the brain for the next day.
• The reverse-learning theory suggests that we dream to forget. Our brains have thousands of neural connections between memories—too many to remember them all—and that dreaming is part of "pruning" those connections.
• In the continual-activation theory, we dream to keep the brain active while we sleep, in order to keep it functioning properly.

Lucid dreams are relatively rare dreams where the dreamer has awareness of being in their dream and often has some control over the dream content. Research indicates that around 50% of people recall having had at least one lucid dream in their lifetime and just over 10% report having them two or more times per month.

It is unknown why certain people experience lucid dreams more frequently than others. While experts are unclear as to why or how lucid dreaming occurs, preliminary research signals that the prefrontal and parietal regions of the brain play a significant role.

How to Lucid Dream

Many people covet lucid dreaming and seek to experience it more often. Lucid dreaming has been compared to virtual reality and hyper-realistic video games, giving lucid dreamers the ultimate self-directed dreamscape experience.

Potential training methods for inducing lucid dreaming include cognitive training, external stimulation during sleep, and medications. While these methods may show some promise, none have been rigorously tested or shown to be effective.

A strong link has been found between lucid dreaming and highly imaginative thinking and creative output. Research has shown that lucid dreamers perform better on creative tasks than those who do not experience lucid dreaming.

Stressful experiences tend to show up with great frequency in our dreams. Stress dreams may be described as sad, scary, and nightmarish .

Experts do not fully understand how or why specific stressful content ends up in our dreams, but many point to a variety of theories, including the continuity hypothesis, adaptive strategy, and emotional regulation dream theories to explain these occurrences. Stress dreams and mental health seem to go hand-in-hand.

• Daily stress shows up in dreams : Research has shown that those who experience greater levels of worry in their waking lives and people diagnosed with post-traumatic stress disorder (PTSD) report higher frequency and intensity of nightmares.
• Mental health disorders may contribute to stress dreams : Those with mental health disorders such as anxiety, bipolar disorder , and depression tend to have more distressing dreams, as well as more difficulty sleeping in general.
• Anxiety is linked to stress dreams : Research indicates a strong connection between anxiety and stressful dream content. These dreams may be the brain's attempt to help us cope with and make sense of these stressful experiences.

A Word From Verywell

While there are many theories for why we dream, more research is needed to fully understand their purpose. Rather than assuming only one hypothesis is correct, dreams likely serve a variety of purposes.

Knowing that so much is left uncertain about why we dream, we can feel free to view our own dreams in the light that resonates best with us.

If you are concerned about your dreams and/or are having frequent nightmares, consider speaking to your doctor or consulting a sleep specialist.

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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? Dreams can feel bizarre but also meaningful, healing or even prophetic at the same time. Many great scientific and technological inventions were inspired by dreams. Niels Bohr first saw the structure of an atom in his dream, Einstein's Theory of Relativity was inspired by a weird dream about cows, and Larry Page, who co-founded Google, was inspired to work on his invention by an anxiety dream.

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However, the proponents of the Activation Synthesis Theory (Hobson and McCarely, 1977) would argue that there isn't a much deeper meaning to dreams. What we experience as dreams is just a creative interpretation of the brain 's random activity during sleep.

• First, we will discuss the activation synthesis theory in psychology, providing an activation synthesis theory definition
• We will delve into various activation synthesis theory examples, before discussing any activation synthesis theory criticisms
• Finally, we will cover the Freud vs activation synthesis theory thesis

Activation Synthesis Theory – psychology

With the development of neuroimaging techniques for studying the brain came new attempts to explain what dreams are. In 1977, psychiatrists Hobson and McCarley proposed their hypothesis on dreaming, based on the neurobiological activity that was observed during REM sleep .

Contrary to Freud's theory (1900), which viewed dreams as the reflection of the unconscious, the Activation Synthesis Theory , although controversial, was supported by neuroimaging evidence .

Activation Synthesis Theory – definition

The Activation Synthesis Theory argues that dreams don't have any inherent meaning , but rather they reflect the random activation of the brain stem during REM sleep . As REM sleep is characterised by greater activity than other sleep stages, which can be compared to the amount of activity during waking hours, the theory focuses only on REM sleep .

The Activation Synthesis Theory posits that dreams are the result of our mind's attempt to make sense of the random physiological brain activity that occurs during REM sleep.

During REM sleep the brain is very active. This brain activation suggests that rich sensory information is processed during this stage, while at the same time all motor and sensory information is blocked out from the brain. This is because of REM atonia (paralysis of muscles during REM sleep) and sensory blockade .

During REM sleep the thalamus activity suggests that all sensory information from the outside is blocked out, so the brain is isolated from the outside world during sleep.

The input that travels to the brain was proposed to be limited to impulses from the body - a result of physiological processes, which occur during sleep. Hobson and McCarley (1977) argued that the cerebral cortex creates elaborate dreams to make sense of activation caused by bodily processes.

Currently, we know that sensory processing does continue during sleep, however much more intense stimuli (louder noises or brighter lights) are needed to elicit arousal and wake us up.

There are two main components of the theory: activation and synthesis.

Activation - during REM sleep the brain appears to be very active even though it is cut off from motor and sensory stimuli. This activation was proposed to be caused by physiological processes, which occur during sleep and was termed random activation .

Synthesis - to make sense of this random activation, initiated by the brain stem, the cerebral cortex activates and compares this activity with our memories. That is how dreams arise, when we experience activation similar to a certain emotional state or activity from our past, a dream simulates it based on that memory .

Activation Synthesis Theory – examples

Let's say that the brain's activity resembles the activity associated with running and fear. Our mind can create a dream in which we are being chased to make sense of this activation.

If the brain areas associated with pain become active our cortex can associate this activity with a recent painful memory of falling out with someone important to us and turn that into a dream.

Activation Synthesis Theory – mechanism

REM sleep is initiated by the activity of the REM-ON area in the brain stem. The sensory input to the body becomes limited and muscles paralysed. Spontaneous activity in the brain stem occurs, possibly linked to other physiological processes which occur in the body at the time.

Other brain areas become activated, for example, the limbic system (responsible for emotional responses), the sensorimotor cortex (responsible for perception and movement) and the cerebral cortex. The cerebral cortex now compares this activity with existing memories and attempts to synthesise it.

Activation Synthesis Theory – Criticism

The Activation Synthesis Theory has inspired further theories of consciousness and dreaming and contributed to the field by providing an evidence-based neurobiological perspective on why we dream.

Still, it remains controversial and has been heavily criticised. Here are the main points of criticism of the theory:

The theory is reductionist, it reduces a complex psychological phenomenon of dreaming into the biological activity of different brain areas. Just because certain brain activity is correlated with dreaming, doesn't necessarily mean that this activity causes dreams or that no other processes are involved. Is the activation a result of dreams, or the cause of dreams?

Evidence for the Activation Synthesis Theory mainly comes from neuroimaging studies of animals. Limitations associated with the accuracy of neuroimaging techniques and animal research limit the validity and generalisability of the theory.

The theory only considers dreams to occur during REM sleep. We now know that dreaming occurs continuously throughout all stages of sleep, which the theory doesn't account for.

Some research suggests that, contrary to what the Activation Synthesis Theory predicts, dreams can be initiated with the activity in the cerebral context, not the brain stem.

The Activation Synthesis Theory can also be criticised for being descriptive rather than explanatory. It explains what might be causing dreams but doesn't explain their purpose.

Freud vs Activation Synthesis Theory thesis

Freud proposed that dreams are a reflection of our unconscious desires and conflicts. Because the unconscious content of our minds tends to be frightening and distressing, we don't usually have access to it. However, dream states allow us to access the unconscious indirectly, the latent content (the deeper meaning of dreams) is disguised in a symbolic manifest content or what we can remember from the dream.

According to Freud dreams do carry an underlying meaning and provide a unique insight into our unconscious, which he believed to control 75% of our behaviour.

In contrast, the Activation Synthesis Theory doesn't support the idea that dreams are very meaningful. It proposes dreams to be a result of random brain activation during sleep, which our mind attempts to interpret based on our memories.

Activation Synthesis Theory of Dreaming (Hobson and McCarley, 1977) - Key takeaways

• The Activation Synthesis Theory, proposed by Hobson and McCarley (1977), posits that dreams are the result of our mind's attempt to make sense of the random brain activity that occurs during REM sleep.
• The brain is isolated from outside sensory input during REM sleep due to the sensory blockade and REM atonia. Still, it remains very active during this stage, and this activity was termed random activation.
• The random activation, initiated by the brain stem, is synthesised by the cerebral cortex, which results in dreams.
• The Activation Synthesis Theory is based on animal studies and was criticised for limited validity and generalisability of evidence, being overly descriptive and reductionist.
• The theory also assumes that brain activity during REM sleep is initiated by the brain stem, which isn't always the case. Moreover, the theory doesn't account for the occurrence of dreams during non-REM sleep.

Frequently Asked Questions about Activation Synthesis Theory

--> what does the activation-synthesis theory explain.

The Activation Synthesis Theory explains how dreams may arise based on the observed neural activity during REM sleep. Dreams result from the aforementioned areas of activity, the brain's attempt to assign meaning to the random firings and activations.

--> What is an example of activation-synthesis theory?

If impulses from muscles trigger activity in the brain stem, the cortex may make sense of this activity by creating a dream about being chased.

--> What is the main idea of the activation-synthesis hypothesis?

The main idea of the Activation Synthesis hypothesis is that dreams are a result of random patterns of brain activation and don't carry any inherent meaning.

--> How does the activation-synthesis hypothesis differ from Freud?

Freud proposed that dreams are meaningful. Dreams reflect unconscious desires and conflicts disguised in symbolic dream content. In contrast, the Activation Synthesis Theory proposed that there is no underlying meaning to dreams, as they merely reflect the random brain activation, which occurs during REM sleep.

--> What is synthesized in the activation-synthesis theory?

In the Activation Synthesis Theory, the random activation in the brain stem, which occurs during REM sleep is synthesised by the cortex as it attempts to make sense of this random activation.

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When do dreams occur according to the Activation Synthesis Theory?

According to the Activation Synthesis Theory, dreams occur during REM sleep, when the brain is isolated from outside sensory information but remains active.

Who proposed the Activation Synthesis Theory?

The theory was proposed by Hobson and McCarley in 1977.

What causes dreams according to the Activation Synthesis Theory?

The Activation Synthesis Theory posits that dreams are the result of our mind's attempt to make sense of the random activation that occurs during REM sleep.

How is the brain isolated from outside sensory information during REM sleep?

This brain is isolated because of  REM atonia (paralysis of muscles during REM sleep) and  sensory blockade .  

What is random activation?

Activation of brain areas observed during REM sleep. Contrary to waking activity it is not caused by outside sensory stimuli.

What is synthesized in the Activation Synthesis theory?

In the Activation Synthesis Theory, the random activation in the brain stem is synthesised by the cerebral cortex.

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Bernard J. Baars is Senior Fellow in Theoretical Neurobiology at The Neurosciences Institute, San Diego.

William P. Banks is Professor of Psychology at Pomona College and editor-in-chief of the journal Consciousness and Cognition .

The late James B. Newman was a member of the Department of Psychology at the Colorado Neurological Institute.

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57: The Brain as a Dream State Generator: An Activation-Synthesis Hypothesis of the Dream Process

• Published: 2003
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J. Allan Hobson, Robert W. McCarley, 2003. "The Brain as a Dream State Generator: An Activation-Synthesis Hypothesis of the Dream Process", Essential Sources in the Scientific Study of Consciousness, Bernard J. Baars, William P. Banks, James B. Newman

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Activation synthesis theory

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Activation Synthesis Theory is a neurobiological theory of dreams , put forward by Allan Hobson and Robert McCarley in 1977 , which states that dreams are a random event caused by firing of neurons in the brain. This random firing sends signals to the body's motor systems, but because of a paralysis that occurs during REM sleep , the brain is faced with a paradox . It synthesizes a narrative by drawing on memory systems in an attempt to make sense of what it has experienced.

The original 1977 theory denied that dreams have meaning or are related to our real world environments. But this point drew criticism from other dream experts. In response, in 1988 , Hobson published a revised theory acknowledging that dreams do reflect past memories, fears, hopes, and desires.

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