Why Do We Dream? From Freud to Activation-Synthesis Theory

From a lecture series presented by Professor Mark Leary, Ph.D.

Why Do We Dream? Sleep research shows that all of us dream each and every night. Every night. Sometimes we remember our dreams, or at least parts of them, but more often we don’t. And if your dreams are anything like mine, that’s probably a good thing.

man asleep for article on why do we dream

Early Sleep Research

Until the 1950s, most scientists who studied sleep assumed that only a small portion of each night’s sleep is taken up by dreams. But then in 1953, sleep researchers noticed that participants in their studies would sometimes flick their eyes back and forth rapidly under their closed eyelids as they slept. And, when the researchers woke participants up to see what was going on, the participants almost always reported that they had been dreaming.

Learn more: Solving Psychological Mysteries

This was the discovery of what’s called rapid eye movement sleep—or REM sleep. Years of research have confirmed that when people are awakened during REM sleep, they report that they have been dreaming 85 to 90 percent of the time. But, when people are awakened when they aren’t in REM sleep—when their eyes are not moving around—they usually don’t report that they were dreaming.

This discovery was important for many reasons, but one was that it allowed researchers to study dreams more carefully than they had in the past. They would just wait until participants in their sleep studies went into REM sleep, and then they’d wake them up to record their dream.

Each night, we pass through series of stages of sleep, each of which is associated with a distinctive pattern of brain waves. In a normal night’s sleep, we cycle through the various stages of sleep several times, usually between 4 and 6, and each of these cycles includes one stage of REM sleep. So, on an average night, each of us dreams on 4 to 6 separate occasions.

…on an average night, each of us dreams on 4 to 6 separate occasions.

The first episode of REM sleep usually occurs about 90 minutes after we first fall asleep, and it’s relatively short. But with each new cycle of sleep stages, the time that we spend in REM gets longer and longer. So, we do most of our dreaming as morning approaches.

Over the course of an average night, we spend about 20 to 25 percent of our sleeping time in REM or dreaming sleep—a quarter of the night—which is far more than researchers once believed. So, you almost certainly did dream last night.

But why? Why do all of us go quietly insane each night, with all of those strange stories and bizarre images and random thoughts? What purpose does all of it serve?

Learn more: Where Do People’s Personalities Come From?

Sigmund Frued Weighs In

Image of "The Sleep of Reason Produces Monsters", by the Spanish painter and printmaker Francisco Goya, 1799
“The Sleep of Reason Produces Monsters”, by the Spanish painter and printmaker Francisco Goya, 1799

As you may know, Sigmund Freud was one of the first people to discuss the purpose of dreaming in detail, and his perspective dominated work on dreaming for many years.

Freud’s psychoanalytic theory suggested that dreams reflect people’s unconscious thoughts and desires. According to Freud, most of our behavior centers around basic sexual and aggressive impulses that have to be fulfilled if people are to be healthy and happy. But because society constrains us from acting on these impulses, and people find the idea that they are a seething cauldron of sex and aggression disturbing, they push awareness of these urges out of their conscious mind.

But, Freud thought that these wishes and desires still needed to be expressed somehow, so they show up in our dreams. In his book, The Interpretation of Dreams, Freud wrote that “wish fulfillment is the meaning of each and every dream.”

Freud admitted that, as you think about your dreams, it might not be obvious to you that most of them deal with satisfying your desires for sex and aggression, but that’s just because your unconscious mind disguises the meaning of your dreams so that you won’t be upset by how disturbing they are.

Now, Freud was a smart and creative fellow, but decades of research have failed to support his views of dreaming. Some practicing psychoanalysts continue to operate as if Freud’s wish fulfillment theory of dreams is true, but, in fact, virtually none of Freud’s claims about the nature of dreams have stood the test of empirical research.

Learn More: Why Do We Have Emotions?

The Science Of REM Sleep

In approaching the question of why we dream, modern researchers suggest that we should distinguish between the brain activity that occurs during REM sleep and the content of the dreams that we have. That is, it’s possible that the brain activity associated with REM sleep is doing something important—that it has some biological function—but that the actual dreams that we experience may not do anything at all.


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Many researchers have suggested that the existence of such a complex brain process as REM sleep—in both mammals and birds—indicates that it’s probably very important. This particular stage of sleep seems to do something that’s necessary for well-being and survival because animals that are deprived of REM sleep—by waking them up every time they enter the REM state—become very disturbed and may eventually die.

But knowing that the physiological state that’s associated with rapid eye movement sleep is important says nothing about the dreams themselves. Even if the brain activity associated with REM sleep is vitally important, the actual dreams that we experience might be just a by-product of those brain states, and that dreams don’t do anything in their own right.

The discovery of REM sleep was important for many reasons, but one was that it allowed researchers to get a better idea about the content of people’s dreams. Before we knew that people dream mostly during a special stage of sleep, researchers had to rely mostly on people reporting their dreams when they woke up in the morning.

But of course, people often don’t remember dreaming at all—even though we know that they did. And the dreams that they do remember in the morning may tend to be the most bizarre or disturbing or vivid ones. So, just asking people to recall their dreams in the morning misses a lot of dreams.

But once REM sleep was discovered, sleep researchers could wake people up during REM and almost always get a report of a dream in progress.

Many of these studies examined the question of whether the content of people’s dreams is affected by things that happen to them either right before they go to sleep or during the REM state itself.

In some studies, people have been shown frightening or emotional movies just before falling asleep, and in other studies, researchers have presented stimuli to people who were presently asleep and in REM. For example, researchers would ring bells, play other sounds, spray sleeping participants with water, introduce odors into the room, or read the names of significant people in participants’ lives. Then, they’d wake the participants up to report their dreams.

But in only about 5 percent of cases was the content of people’s dreams affected by events in the environment that occurred either immediately before or during sleep. So these studies have led researchers to conclude that the content of our dreams is not affected much by what’s going on around us at the time.

…studies have led researchers to conclude that the content of our dreams is not affected much by what’s going on around us at the time.

Even so, the occasions on which people do incorporate stimuli in their environment into their dreams are interesting because they show how quickly and ingeniously the brain fits those stimuli into dreams that are already in progress.

So, for example, in a dream about traveling down a river in the jungle, a sleeping research participant may incorporate a bell that’s rung in the laboratory into the dream as someone ringing a bell from the shore to warn that aggressive natives are nearby.

This ability to incorporate incoming information into a dream shows that the brain is functioning at a very high and flexible level during REM sleep.

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Activation-Synthesis Theory

That’s the view taken by the first modern theory of dreams—it’s called activation-synthesis theory—which is still accepted by many dream researchers. The main idea behind activation-synthesis theory is that dreams are just the brain’s efforts to make sense out of meaningless patterns of firing in the brain as we sleep. Certain circuits in the brain become activated during REM sleep, and then higher areas of the brain try to interpret this activity and find meaning in it. Those patterns of firing don’t really mean anything, but the brain tries to make sense out of them anyway.

According to this theory, then, our dreams are often disjointed and strange because higher cognitive areas of the brain are trying to interpret signals that are just by-products of activity going on in other parts of the brain. Activation-synthesis theory has enjoyed a good deal of scientific acceptance, but research evidence for it is somewhat mixed. And, the theory says relatively little about why our dreams have the content that they do.

Even if it can be shown that dreams are the brain’s efforts to interpret ambiguous signals from other parts of the brain, why does the brain interpret these signals in one way rather than in another?

In any case, according to activation-synthesis theory, dreams are essentially a useless by-product of other brain processes that are occurring as we sleep.

Read about modern sleep studies in part two of this series of articles on dreams.
From The Lecture Series Understanding the Mysteries of Human Behavior
Taught by Professor Mark Leary, Ph.D.

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