What is Rapid Eye Movement (REM) Sleep?

REM Sleep is one of the three states of consciousness. Read on the learn what happens during this mysterious sleep stage and the questions that remain to be answered.

By Andrea Pisani Babich

Apr 25th, 2022

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Expert Insights from Dr. Anna Pickering a medical writer who received an honors baccalaureate of science in biochemistry and biophysics, minoring in chemistry, from Oregon State University and her doctorate in cell and molecular biology from the University of Hawaii at Manoa’s John A. Burns School of Medicine.

Rapid Eye Movement (REM) sleep is one of the four stages of our sleep cycle and is easily recognized by its eponymous rapid eye movements from side to side under closed eyelids. “Common signs that a person is in REM sleep include twitching of their face and limbs as well as quick or irregular breathing,” says Dr. Pickering.

Other characteristics of REM sleep include:

  • quick and irregular breathing
  • increased heart rate
  • increased blood pressure
  • body temperature that reflects the temperature of your bedroom instead of decreasing as it does during the first three stages of sleep
  • brainwave activity similar to that while we are awake
  • sexual arousal in both men and women
  • twitching of the face and limbs
  • tendency towards obstructive sleep apnea due to lack of muscle tone within airways

But there is much more to know about REM sleep than just these descriptions. Our current knowledge of this stage of sleep is limited partly because it is a relatively new field of study and partly because of prevailing attitudes about sleep.

What is REM Sleep?

REM sleep occurs in cycles of about 90-120 minutes throughout the night, and it accounts for up to 20-25% of total sleep time in adult humans, although the proportion decreases with age (a newborn baby may spend 80% of total sleep time in the REM stage). 

In particular, REM sleep dominates the latter half of the sleep period, especially the hours before waking, and the REM component of each sleep cycle typically increases as the night goes on.

Related: Sleep wake homeostasis

As the name suggests, it is associated with rapid (and apparently random) side-to-side movements of the closed eyes, a phenomenon which can be monitored and measured by a technique called electrooculography (EOG). This eye motion is not constant (tonic) but intermittent (phasic). 

It is still not known exactly what purpose it serves, but it is believed that the eye movements may relate to the internal visual images of the dreams that occur during REM sleep, especially as they are associated with brain wave spikes in the regions of the brain involved with vision (as well as elsewhere in the cerebral cortex).

A Brief History of Sleep Research and REM Sleep

In 1924, a piece of technology called the electroencephalogram (EEG) was invented to study how the human brain functions during different activities and experiences, including sleep. By 1928, a man named Hans Berger was recording legible patterns of brainwave activity. But it wasn’t until 1953 that Dr. Eugene Aserinsky discovered rapid eye movements during sleep.

In the following five years, Dr. William Dement used the EEG to identify the sleep cycle and its four stages of sleep that are defined by changes in the brain’s electrical activity. Since then, researchers have learned a lot about the mysteries of sleep, primarily that sleep is not a time of total inactivity, a notion that even educated people clung to. This belief appears to have delayed the progression of sleep study. In fact, there is so much going on while we sleep, that for as many answers scientists have discovered, they have raised new questions including:

  • What is the function of sleep?
  • What is the exact role of each stage of sleep?
  • What is the function of dreams?
  • How does REM sleep influence memory formation?

Here is what we do know about REM Sleep.

Dreams and REM Sleep

The majority of dreams – certainly the most memorable and vivid dreams – occur during REM sleep, and it is thought that the muscular atonia that accompanies it may be a built-in measure to protect us from self-damage which could occur while physically acting out these vivid REM dreams. 

This hypothesis is borne out by Michel Jouvet’s early experiments on cats in which the muscle inhibition nerves were severed, leading these cats to physically stalk invisible prey and run and jump around wildly during the dreams of REM sleep.

Our dreams occur during this fourth stage of sleep, and they tend to be more vivid than the few dreams we may have earlier in our sleep cycles. Most dreams we remember occur during the longest REM sleep stage that happens just before we awaken, although dreams may occur throughout the night as many as seven times.

Dreaming is one of the many aspects of sleep that we still don’t understand. Scientists do not agree on the purpose of dreams, but there seems to be no shortage of theories.

Some theories about the role of dreams include:

  • Memory consolidation theory. Some scientists believe that our dreams bear some resemblance to events in our waking lives and that they help us to sort out important memories from unimportant ones. Those memories deemed important are processed into long-term memory.
  • Threat simulation theory. Subscribers to this theory think that our dreams provide us with opportunities to rehearse how to escape danger, injury, or death in threat scenarios. They suggest that dreams evolved as a way to help our primitive ancestors survive. Early humans who could avoid danger most effectively because they had prepared escape strategies in their dreams were more likely to survive than those who were unprepared. Dreams that prepared them for possible dangers and how to avoid them gave them an edge over their doomed peers who did not practice in the safety of their own minds.
  • Housekeeping theory. Francis Crick, who co-discovered the DNA helix, and Grahame Mitchison hypothesized that dreams act as an “unlearning” mechanism. According to this theory, dreams identify unwanted thoughts or erroneous information, and erase them from the brain lest they become the basis of obsession, paranoia, or other pathologies that prevent the brain from working efficiently.
  • Problem solving theory. Similar to the threat simulation theory, in this theory, dreamers act out scenarios or problems in their dreams and test out solutions that might be too threatening in their waking lives.
  • Multiple roles. There is no reason to believe that dreams serve only one of these purposes. Perhaps dreams fill all of these roles on an “as needed” basis.
  • No role. There are still some sleep experts who believe that, by and large, dreams are merely visual representations of random brain cell activity during sleep.

REM Sleep Behavior Disorder

“If you’re frequently acting out in your dreams and experiencing jerky arm and leg movements while you sleep, you may be suffering from REM Sleep Behavior Disorder,” says Dr. Pickering.

REM Sleep Behavior Disorder (RBD) is a condition that causes people to act out their dreams, often unpleasant ones, through speech or physical movement. RBD can be characterized by jerky arm and leg movements or even full, violent episodes during sleep.

During REM sleep, our bodies are almost completely immobilized to the point of paralysis to prevent us from acting out what we dream. When this mechanism fails and people begin to move in response to what they are dreaming, they may be diagnosed with REM Sleep Behavior Disorder (RBD). This rare diagnosis is usually preceded by injury to themselves or their bed partners as a result of sleepers acting out their dreams, which are very vivid during REM sleep. In fact, once a woman swallowed her engagement ring in her sleep as the result of a nightmare on a high-speed train with bad guys who could potentially steal her sentimental piece of jewelry.

Related: What is REM rebound?

Dreams that are violent or frightening could prompt the sleeper to scream, shout, punch, kick, or even jump out of bed and run from the room. Researchers have estimated that RBD affects only about .5% of the population, 90% of whom are male and over 50 years old. Also, people who take antidepressants, are going through withdrawal, or are suffering from PTSD have a higher chance of suffering from RBD.

Those with REM sleep behavior disorder often later develop other neurological disorders including Parkinson’s disease, sudden dramatic drops in blood pressure, loss of smell, and cognitive impairment. Since REM sleep is regulated in the brainstem, the changes in this part of the brain that trigger these other neurological disorders also disrupt the normal muscle atonia of REM sleep.

“Possible treatments for REM Sleep Behavior Disorder include Clonazepam, which has proven to be highly effective, some antidepressants, or melatonin,” says Dr. Pickering. “Consult with your doctor about your sleep behavior to find the best course of action.”

REM Sleep and Depression

Research has shown that deprivation of REM sleep may not have an effect on non-depressed people. While they compensate for their REM debt by having more of it when they are able to, there appear to be no long-term, adverse physical or psychological effects. All of which raises lots of questions about the function of REM Sleep. Do we need it or not? If so, why?

However, at least one sleep study of depressed people showed that skipping REM sleep, and therefore dreams, helped 9 of 12 of them to get past their depression in the five months of the study. Dr. Rosalind Cartwright, chair of psychology at Rush-Presbyterian-St. Luke’s Medical Center, told WebMD, “Depressed people don’t solve problems during their dreams, like other people do. They pile up their troubles, and the last dream of the night is the worst. They wake up in a worse mood if you let them sleep through those dreams. But if you interrupt them, they normalize and feel better in the morning.”

This was a small study and not everyone agrees with Cartwright’s findings. While some researchers see potential for further research in her conclusion, they note that the lift in mood is not long lasting and generally reverses after two or three days. But, certainly, Cartwright’s findings are tantalizing data points in the study of REM sleep and depression.

It is also important to note that some recent research suggests REM is involved in regulation of emotional memories, and that REM disruption may contribute to mental health disorders like depression, anxiety, or PTSD.


Plenty of research needs to be done in the field of sleep and its various stages. We’re here to help you get the best night’s sleep possible and live life to the fullest. Stay tuned to Mattress Advisor for the latest news in the study of sleep as it unfolds.

Expert Bio

Expert Bio

Dr. Anna Pickering is a freelance medical writer based in Portland, OR working for The Med Writers. She received an honors baccalaureate of science in biochemistry and biophysics, minoring in chemistry, from Oregon State University and her doctorate in cell and molecular biology from the University of Hawaii at Manoa’s John A. Burns School of Medicine. Before transitioning to writing she completed a year of postdoctoral research at Oregon Health and Science University and worked briefly at the biotech startup Ayumetrix.