How Dreams Work

By: Lee Ann Obringer & Yves Jeffcoat  | 
Why humans dreams has puzzled us for eons. Do you remember what you dreamed last night? Boris SV/Getty Images

Humans have always dreamed. Yet the phenomenon of dreaming has long been puzzling and fascinating. And for good reason: Dreams can be vivid, exciting and sometimes terrifying. But as many questions as neuroscientists, psychologists and philosophers have asked about dreams, the purpose of dreaming is still nebulous. Are they strictly random brain impulses, or are our brains actually working through everyday issues while we sleep as a sort of coping mechanism? Should we even bother to interpret our dreams? Many people say that we have a great deal to learn from our nighttime narratives.

In this article, we'll talk about the major dream theories, from Sigmund Freud's view to the hypotheses that claim dreams are random. We'll find out what scientists say is happening in our brains when we dream and why we have trouble remembering dreams when we wake up. We'll also cover recurring dreams and nightmares.


For centuries, we've tried to figure out just why our brains play these nightly shows for us. Researchers continue to toss around many theories about dreaming. According to Sidarta Ribeiro, a neuroscientist and author of the book "The Oracle of Night: The History and Science of Dreams," those theories essentially fall into two categories:

  1. theories that claim dreams have meaning
  2. theories that claim dreams have no meaning

Ribeiro supports theories that fall in the former camp. Still, he says, there is a long tradition of anti-Freudian thinkers who say that dreams are nothing more than a byproduct of brain activity.

In the next section, we'll look at the different stages of sleep.

Dreaming and the Brain

sideview of body
The brain, and how it responds to the four stages of sleep, affects how and when we dream. Hank Grebe/Getty Images/Purestock

There are four stages of sleep. Previously, there were five stages, but in 2007 Stages 3 and 4 were combined. The first three stages compose non-rapid eye movement sleep (NREM). Stage 1 of NREM sleep is a short, light sleep characterized by slow eye movement and the appearance of theta waves.

In stage 2, the muscles become more relaxed. Electroencephalography (EEG) recordings show sleep spindles — bursts of rhythmic brain wave activity — and K-complexes, or brief, high-amplitude waves.


Stage 3, also known as slow-wave sleep, is the deepest stage of NREM sleep. During this stage, delta waves emerge, and the brain is less responsive to external stimuli. It is difficult to wake the sleeping person. Our brain activity throughout these stages is gradually slowing down so that by deep sleep, we experience nothing but delta brain waves, the slowest brain waves (see sidebar).

After stage 3, about 90 minutes after we go to sleep, we begin rapid eye movement sleep (REM sleep). REM sleep is primarily characterized by movements of the eyes and is the fourth stage of sleep. Other mammals, birds and reptiles exhibit REM sleep, too.

Eugene Aserinsky, a graduate student in physiology at the University of Chicago, and physiologist Nathaniel Kleitman discovered REM sleep in 1953. They found that the brain is in an active waking state during REM sleep, and that it alternated with quiescent sleep periods. The discovery of REM sleep kickstarted a flurry of scientific research into the mechanisms of the sleeping brain.

During REM sleep, several physiological changes also take place. The heart rate and breathing quickens, and blood pressure rises. We can't regulate our body temperature as well, and our brain activity increases to the same level as when we are awake. The rest of the body, however, is essentially paralyzed until we leave REM sleep.

According to a 2012 study in rats at the University of Toronto, this paralysis occurs when the neurotransmitters gamma-aminobutyric acid (GABA) and glycine turn off activity in the motoneurons (neurons that conduct impulses outward from the brain or spinal cord). Because REM sleep is the sleep stage at which most dreaming takes place, this paralysis could be nature's way of making sure we don't act out our dreams physically. Otherwise, if you're sleeping next to someone who is dreaming about playing kickball, you might get kicked repeatedly while you sleep.

Throughout the night, we go through these four stages several times. Each subsequent cycle, however, includes more REM sleep and less deep sleep (stage 3). As a typical adult nears the end of their sleep episode, REM sleep increases, and stage 2 accounts for the majority of NREM sleep.

Sleep patterns do change as we age, though. The total amount of time we spend sleeping decreases (though we require the same amount of sleep from our 20s into old age); the proportion of time we spend in slow-wave sleep and REM sleep decreases; and our ability to maintain sleep decreases. That said, a person's sleep architecture, or basic structure of normal sleep, varies depending on age.

Although most dreams take place during REM sleep, dreams can occur during any of the sleep stages. Most NREM dreams, however, don't have the intensity and narrative structure of REM dreams. And we're most likely to remember dreams we have during REM sleep. The length of dreams vary. It's hard to tell exactly how long they last, but we dream multiple times a night, and dreams likely last anywhere from a few minutes to more than 30 minutes. We may spend around two hours dreaming each night.

In the next section, we'll look at some of the major dream theorists and what they say about why we dream.

Dreams: The Theoretical Divide

girl dreaming
There are many different theories about dreaming, but no consensus on its purpose. Maarten Wouters/Getty Images

First and foremost, in dream theory is the founder of psychoanalysis, Sigmund Freud. Falling into the psychological camp, Freud's theories are based on the idea of repressed longing — the desires that we aren't able to express in a social setting.

Dreams allow the unconscious mind to act out those unacceptable thoughts and desires. For this reason, his theory about dreams, as described in his book "The Interpretation of Dreams," focuses primarily on sexual desires and symbolism.


For example, any cylindrical object in a dream represents the penis, while a cave or an enclosed object with an opening represents the vagina. Freud lived during the sexually repressed Victorian era, which in some way explains his focus.

Carl Jung studied under Freud but soon decided his own ideas differed from Freud's to the extent that he needed to go in his own direction. Jung agreed with the psychological origin of dreams, but rather than saying that dreams originated from our primal needs and repressed wishes, he felt that dreams allowed us to reflect on our waking selves and solve our problems or think through issues.

More recently, around 1977, researchers Allan Hobson and Robert McCarley set forth another theory that threw out the old psychoanalytical ideas. Their research on what was going in the brain during sleep gave them the idea that dreams were simply the result of random electrical brain impulses that pulled imagery from traces of experience stored in the memory.

According to this model, known as the activation-synthesis hypothesis, dreams are the result of physiological processes. The forebrain is attempting to make sense of the signals that fire during REM sleep. Hobson described five key characteristics of dreams:

  1. illogical content
  2. odd sensory experiences
  3. intense emotions
  4. acceptance of strange events
  5. difficulty in remembering them

This theory was controversial because of its leap away from the accepted theories, but it has evolved since Hobson and McCarley introduced it. Expanding on the activation-synthesis hypothesis, Hobson proposed the AIM model, which describes the importance of brain activation, input-output gating and chemical modulation to the dreaming process. Still, this theory is limited and does not fully explain why we dream.

Francis Crick, the scientist best known for his role in identifying the structure of DNA, proposed that we dream to forget. During dreams, he posited, we replay the events of the day so that we can erase the random, hybrid associations that we craft from real memories and strengthen the legitimate memories. He called it "reverse learning." Crick did not think that his explanation was comprehensive enough to completely explain dreaming, but he did think that it was a good starting point. In 1983, Crick and Graeme Mitchison published a paper in the journal Nature expounding on their proposed mechanism of reverse learning.

Mainstream science has largely discounted Freud's dream theories, yet theories about why we dream abound. Psychology professor G. William Domhoff proposed a neurocognitive theory of dreams that detailed the similarities of dreams and waking thought. He concluded that dreams likely have no adaptive function in an evolutionary sense. The self-organization theory of dreaming suggests that the brain combines signals into a relatively continuous narrative during sleep. And the threat simulation theory of dreaming states that we dream to rehearse threatening situations, so that we are better prepared to face danger in the waking world.

The list goes on; contemporary hypotheses claim that dreaming helps us process emotions, clear mind clutter, maintain proper brain function and promote creativity. Considering the complexity of dreaming and the difficulty of studying it, a consensus on its purpose will be hard to reach.

Let's look at what happens if you don't get any REM sleep.

Dreams and REM Sleep

What happens if you don't get any REM sleep? Originally, researchers thought that no REM sleep meant no dreams. Now, scientists have confirmed that dreaming is not confined to REM sleep, and that people dream during NREM sleep.

Researchers have also determined that people can function with no major adverse effects when they are deprived of REM sleep, but we cannot survive without NREM sleep. People who have injuries to the brainstem, which controls REM, do not face adverse psychological effects due to REM dreaming deprivation.


Yet, in the study of dreams, people are often awakened during REM sleep so that they can give dream reports. Dream reports taken at this time are typically longer, more vivid, more emotional and more structured than those taken after NREM sleep. And lucid dreams, or dreams in which people are aware that they are dreaming, usually occur during REM sleep.

In people who have REM sleep behavior disorder (RSBD), the body does not experience temporary paralysis, or muscle atonia, as is typical during REM sleep. Instead, they act out their vivid dreams through sudden movements and vocalizations. RSBD is a parasomnia, or a disorder involving unusual experiences that disrupt sleep. Many researchers would argue that dreaming cannot be divorced from REM altogether.

Still, some researchers say that there isn't much connection between the two, though most believe that dreaming is likely influenced by REM. Even though REM sleep is no longer synonymous with dreaming, there is still debate over the exact relationship between dreaming and REM.

Dream Recall

woman dreaming
Some people say they never dream. Research isn't sure if this is true, or if these people simply don't remember their dreams. Thomas Barwick/Getty Images

It is said that five minutes after the end of a dream, we have forgotten 50 percent of the dream's content. Ten minutes later, we've forgotten 90 percent of its content. Why is that? We don't forget our daily actions that quickly.

There are some people who say that they never dream. It's unclear if this is possible, but we do know that some people rarely or never remember their dreams. In the early 2000s, neuropsychologist and psychoanalyst Mark Solms found that people who developed lesions in the white matter of their medial prefrontal cortex reported that they stopped dreaming. Dream recall can vary person to person, but it can also vary day to day for one person.


Researchers have been studying dream recall for decades. Even so, we don't know whether people who never remember their dreams actually dream less than people who frequently remember their dreams, or whether they are just forgetting their dreams more easily. People who have reported never remembering their dreams have been able to recall them when they are awakened at the right moment. Many people have formed hypotheses about why remembering dreams is so notoriously difficult.

Freud theorized that we forget our dreams because they contain our repressed thoughts and wishes, so we don't want to remember them anyway. Other research points to the simple reason that other things get in the way. We are forward-thinking by nature, so remembering something when we first wake up is difficult.

Dreams may be so hard to remember because the hippocampus, a structure in the brain responsible for learning and memory processes, is not fully active when we wake up. This could result in a dream being present in our short-term memory, but not yet able to move to long-term storage.

Some researchers believe that changing levels of the neurotransmitters acetylcholine and norepinephrine are part of the reason we forget our dreams. Others think that some dreams may just be too useless to remember, so the brain tends to discard them. And some scientists think that people with certain personality traits — like those who are prone to daydreaming and introspection — have less difficulty remembering their dreams.

Despite the unknowns around dream recall, there are some measures that we can take to increase the likelihood that we remember our dreams when we wake from our slumber.

Those who believe we have a lot to learn about ourselves from our dreams are big proponents of dream journals. Here are some steps you can take to increase your dream recall:

  • "Well, the first thing is that people need to understand, they need to sleep long enough to remember their dreams. Because the second half of the night is the one that is dominated by REM sleep," neuroscientist Ribeiro says. "If you cut your sleep short, you will tend to have poor dreams to report."
  • Ribeiro also says that what you do before going to bed is important. Activities like drinking alcohol, using cannabis, or exercising too late can negatively affect the quality of our dreams and our ability to remember our dreams upon waking.
  • When you go to bed, tell yourself you will remember your dreams.
  • If we wake up straight out of a dream, we are more likely to remember it. We are also more likely to remember dreams that are vivid and coherent. Set your alarm to go off every hour and half so you'll wake up around the times that you leave REM sleep, when you're most likely to remember your dreams. (Or, drink a lot of water before you go to bed to ensure you have to wake up at least once in the middle of the night!)
  • Keep a pad and pencil next to your bed.
  • Try to wake up slowly to remain within the "mood" of your last dream. "People will be quite surprised that after years of not remembering anything," says Ribeiro, "they can suddenly remember pages and pages of dreaming."

Controlling Dreams

lucid dream
Many scientists theorize you can induce, or even control, your dreams using a variety of techniques. Ezra Bailey/Getty Images

We are typically unaware that we are asleep while we are in the throes of an emotional dream. But it is possible to be aware that we are dreaming, and it's even possible to gain control over our dreams.

Lucid dreaming occurs when you realize that you are dreaming. In some cases, the sleeping person can control what happens in the dream narrative. Some lucid dreams occur spontaneously, but people can also learn how to lucid dream. It is estimated that half of all people will have at least one lucid dream during their lifetime. But overall, lucid dreaming is rare, and even people who tend to lucid dream do so infrequently.


Lucid dreaming is mentioned throughout history, though the term wasn't coined until 1913 by Dutch psychiatrist Frederik van Eden. Paul Tholey, a German dream researcher who was involved in lucid dream research at Goethe University, developed a technique to induce lucid dreams in 1959. The reflection technique, as he called it, required people to ask themselves throughout the day if they were awake or dreaming. Budding lucid dreamers can also practice recognizing odd occurrences, or dream signs, that suggest they are in a dream and not reality.

Psychophysiologist Stephen LaBerge, scientist Denholm Aspy, and other dream researchers have studied lucid dreaming techniques extensively. They refer to a technique similar to Tholey's reflection method that they call "reality testing." This technique and one called the mnemonic induction of lucid dreams (MILD) have been among the most successful techniques for inducing lucid dreaming.

Reality testing involves questioning whether you are awake or dreaming throughout the day, then performing a test to determine which state you are in. Reliable reality tests could be rereading written text or closing your lips and inhaling. The hope is that if you make these actions habits while you are awake, then you can perform them reflexively when you are dreaming. These reality tests can cause strange occurrences in your dream, alerting you to the fact that you are dreaming.

The MILD technique involves similar reminders to the reality testing method but focuses those reminders at night rather than throughout the day and night. Before sleeping, the dreamer should repeat a mantra such as "next time I'm dreaming, I will remember that I'm dreaming." Then, you focus on reentering a recent dream and looking for clues that it is indeed a dream. You imagine what you would like to do within that dream.

For example, you may want to fly, so you imagine yourself flying within that dream. You repeat these last two steps (recognizing when you're dreaming and reentering a dream) until you go to sleep.

The MILD technique is often paired with the wake back to bed (WBTB) technique, where a person wakes up five or six hours after falling asleep and remains awake for a short time before falling back asleep. This could help increase mental alertness and target the REM sleep stage, when most lucid dreaming occurs.

Using these techniques, people have been able to have lucid dreams at will. Because this type of technique takes such mental training, however, some companies have introduced devices that attempt to induce lucidity through external stimuli.

While lucid dreaming may just seem like a cool way to enter fantasy land, it also has several applications outside of recreation. Lucid dreaming can help in personal development, enhancing self-confidence, overcoming nightmares, improving mental (and perhaps physical) health and facilitating creative problem-solving. For instance, lucid dreams could help reduce symptoms of anxiety or post-traumatic stress disorder.

Finally, lucid dreaming can function as a "world simulator." Just as a flight simulator allows people to learn to fly in a safe environment, lucid dreaming could allow people to learn to live in any imaginable world and to experience and better choose among various possible futures.

"How much you can practice your skills in the simulated world inside your own brain is, I think, a frontier of research," says Ribeiro.

Dream Incubation

image of 'heaven'
Another dream technique called dream incubation is when you "plant a seed" for a what you want to dream about. So if you want to dream about what heaven looks like, you would tell yourself that you'll dream about that before you go to bed. Kiratsinh Jadeja/Getty Images

Dream incubation is learning to plant a seed for a specific dream topic to occur. For example, you might go to bed repeating to yourself that you'll dream about a presentation you have coming up or a vacation you just took. Those who believe in problem solving through dreams use this technique to direct their dreams to a specific topic.

While somewhat similar to lucid dreaming in that problems can be solved, dream incubation is simply focusing attention on a specific issue when going to sleep. Several studies have shown this method to be successful over a period of time.


For example, Harvard psychiatrist Deirdre Barrett found in her research that it was certainly possible to come up with novel solutions in dreams that are both personally satisfying and reasonable to an outside observer. People have used dreams to solve problems with visual solutions and problems that require more creative, abstract solutions.

Ribeiro says that using the time before you go to sleep to set your intentions for your dreams can be effective. He says the following:

In the West world, people act as if dreams are something that happen to them. But among Native Americans, for example, people often go to the dream experience not as somebody that is being hunted by the dream, but as somebody that is hunting the dream, that is going after the dream. You have an intention. 'I want to solve a problem. I have a question regarding my family, regarding my work, regarding my most intimate problems.' You could, you should present those things to your dream as a way to seek advice and seek guidance. And this is a way to dream that is more aligned with with the ways by which dreaming evolved.

Throughout history, inventors, writers, artists and scientists have credited their dreams for many of their biggest successes.

  • Kekulé, the German chemist who discovered the structure of the benzene molecule, had worked endlessly to figure it out. Then, in a dream, he saw snakes forming circles with their tails in their mouths. When he awoke, he realized that the benzene molecule, unlike all other known organic compounds, had a circular structure rather than a linear one.
  • The inventor of the sewing machine, Elias Howe, struggled in 1884 to figure out how the needle could work in a machine for sewing. He supposedly had a dream where he was surrounded by warriors with spears that had a hole in the point. When he woke up, he realized that a needle with a hole in the point would solve his problem.
  • Mary Shelley, author of "Frankenstein," got the idea for the famed book in a dream.
  • Many musicians, including Paul McCartney, Billy Joel and Beethoven, reportedly found inspiration for their music in their dreams. Some hear musical arrangements in their dreams, while others hear lyrics.

What Do Our Dreams Mean?

dream of falling from the sky
"What does my dream mean?" is one of the questions we still can't quite answer. That's because a dream about falling from the sky could mean one thing to you and something entirely different to someone else. Matthias Clamer/Getty Images

Those on the physiology side of the "why we dream" argument see dreams as nonsense that the brain creates from fragments of images and memory. For them, dreaming may serve a purpose, but the content of dreams is not inherently meaningful.

For centuries, however, people have looked at their dreams as both omens and insights into their own psyches. Many think dreams are full of symbolic messages that may not be clear to us on the surface, but can be interpreted if we dig deeper. Mainstream science does not support one-size-fits-all dream interpretations. But that does not mean that dreams are meaningless.


The art of interpreting dreams goes back thousands of years. People have long turned to guides that equate certain dream symbols with fixed meanings. While these fixed interpretations may not be accurate for everyone, a person's dreams may still have personal significance.

In the book "The Oracle of Night: The History and Science of Dreams," Ribeiro points to the existence of recurring dreams as evidence that dreams have meaning. "It would be impossible for dreams to repeat if their genesis were entirely accidental," he says in the book.

For many years, people have been working with their dreams in psychotherapy. Freud's "The Interpretation of Dreams" jumpstarted the popularity of dream interpretation in psychoanalysis. Freud considered dream interpretation to be a road into "knowledge of the unconscious activities of the mind."

Dream work is also used in other therapeutic schools, like family therapy and cognitive behavioral therapy. Some therapists encourage their clients to explore and analyze their dreams. Focusing on dreams during therapy sessions can allow clients to share emotions, memories and behaviors with a therapist that they might not otherwise divulge. Dreams can provide clinically useful information and highlight emotional concerns.

Relying on dream interpretation guides to elucidate dreams about cheating partners, bears or falling off of cliffs is likely a futile effort. But discussing our dreams and understanding what they mean to us individually can be beneficial.

Recurring Dreams and Nightmares

Nightmares are perhaps the worst kind of dreams because they can cause fear and anxiety. They also occur more in children than adults. kampee patisena/Getty Images

Many people have the same or a similar dream many times, over either a short period of time or during their lifetime. Recurring dreams often emerge during times of stress. They have many different themes, but there are some subjects that pop up frequently, like being chased or failing a test. These dreams can be positive or negative.

Sometimes, recurring dreams are symptoms of PTSD or generalized anxiety disorder. They may represent a way to process trauma or practice avoiding threats, but it's not completely clear why they occur.


Nightmares are dreams that are so distressing they usually wake us up, at least partially. Nightmares can occur at any age but occur in children more than adults. Nightmares usually cause strong feelings of fear, sadness or anxiety. Their causes are varied.

Some medications (or withdrawal from them) cause nightmares. Traumatic events also cause nightmares. Recurrent nightmares are also associated with acute stress disorder, anxiety and depression. Persistent nightmares can have a range of adverse effects — they can cause sleep deprivation, they can interfere with relationships and they have been linked to self-injury and suicide.

If a health condition is contributing to the nightmares, then treatment addresses that underlying condition. Some sleep centers offer nightmare therapy and counseling. Nightmares associated with PTSD have been treated with imagery rehearsal therapy, where the affected person changes the ending to the nightmare while awake so the dream is no longer threatening.

People with PTSD, depression or anxiety also may take medication to alleviate the feelings leading to their nightmares. People who have nightmares could also benefit from lifestyle changes like exercising, practicing relaxation techniques and avoiding stimulants before bed.

Another method of treating nightmares is through lucid dreaming. Lucid dreaming may allow people to reduce the frequency, intensity and distress of nightmares, but more research is needed to form clearer conclusions.

Unlike nightmares that occur during REM sleep, night terrors generally occur during non-REM sleep, usually in the first cycle of the deepest phase of sleep (within the first hour or two of going to bed). Night terrors can last anywhere from a few minutes to 30 or 40 minutes.

People having night terrors are still asleep but may look like they are awake. For example, they may sit up in bed screaming with their eyes wide-open. When they actually do wake up, they usually have no memory of the episode (although some people do remember them). Night terrors occur most frequently in children, but adults can also experience them.

Premonitions and the Future of Dream Research

The science of dreams is obviously not a clear-cut one. While many believe our dreams mean something, there are also many who don't. But what about dreams that have foretold future events? Has this simply been coincidence? Scientific research does not support the existence of premonitions in dreams.

But Ribeiro argues that there is nuance; we can understand precognitive dreams in a neurobiological manner rather than a metaphysical one. He notes how throughout history and across the world, dreams have been treated as tools for the exploration of the future. They were gateways for people to get advice, knowledge and insight. We are now detached from that, he says.


"In the European-centered tradition of science and capitalism, dreams lost entirely the importance for socialized matters, for scientific matters, for state matters, for military matters," says Ribeiro. "It doesn't make any sense anymore. A CEO wouldn't go in a meeting with the board of directors and say, 'I had a dream that we should do this and that.' This will disqualify that person immediately."

He says that by replacing dreams with science, we've gained a way to predict the future in quantitative and effective ways. But we've also lost touch with an old mechanism that has been of central importance throughout the human lineage.

Research in various areas of dreaming is ongoing, particularly in the areas of REM sleep and lucidity. Scientists posit that two-way communication with people who are dreaming is possible. Researchers are also developing sleep-tracking devices that can help record dream reports and guide dreams in certain directions.

According to Ribeiro, we must understand the history and science of dreams because sleeping and dreaming are important to our health as individuals and as a society. The reduced emphasis we place on sleep and dreaming across the world today may be harmful, he says.

"We should not think that the ability to dream and recall dreams and share dreams is something that will not be necessary in the future, that is not necessary now," says Ribeiro. "We need to go back to dreaming and go back to dream sharing and go back to collective dreams if we want to stay around for much longer."

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