What Is REM Sleep?

A Sleep Stage With Eye Movement, Vivid Dreams, and Muscle Paralysis

Rapid eye movement (REM) sleep is one of the two recognized types of sleep. It is differentiated from non-REM sleep by vivid dreams, paralysis of most of the body’s muscles, and preserved movement of the eyes and diaphragm. It occurs at intervals of 90 to 120 minutes throughout the night and becomes more prolonged towards morning.

The last third of the night often has an increased presence of REM sleep and it is common to wake from it in the morning. A healthy young adult will spend about 20% to 25% of the night in REM sleep and it occurs in four to six discrete episodes. It is important formemory processing and problem-solving.

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How the Brain Produces REM

REM sleep is generated within the brain through a distributed network, rather than there being a single responsible area. Specific signs of REM sleep are generated by unique groups of cells within the pons of the brainstem. The generator for the loss of muscle tone is located in the pericoeruleus/locus coeruleus alpha part of the subcoeruleus area.

Input is received from the pedunculopontine tegmental (PPT) cells to turn REM on and from the locus coeruleus and raphe nucleus to turn REM off. Neurons that generate P-waves in the subcoeruleus area are critical for the consolidation of memory. 


Nathaniel Kleitman, a professor of physiology at the University of Chicago, was central to the discovery of REM sleep. In 1951, he assigned a graduate student named Eugene Aserinsky to investigate the movements of closed eyes of sleeping infants to better understand the perceived cycles of different sleep types.

He was joined by William C. Dement in 1952, who is widely regarded as the father of modern sleep medicine. They developed a method of electrooculography to measure eye motility continuously without requiring tedious direct observation with a flashlight.

They observed the rapid eye movements were associated with irregular respiration and accelerated heart rate, and later demonstrated it was associated with vivid dreaming. They published an important paper on their findings in 1953.


Beyond the curiosity of its presence as an integral part of sleep, REM sleep seems to serve some important functions. It is a time in which the brain is very active, with high metabolic activity noted.

As the body is normally actively paralyzed during REM sleep, it is possible to experience vivid dreams without the danger of acting those dreams out. There are clear variations in physiological measures, suggesting that the body’s systems may be revved up during the state. Males may be noted to have erections during this time. 

As noted above, REM sleep also appears to have important roles in the consolidation of memory. This may involve paring down connections between neurons that are unnecessary and also making unique associations that may promote problem solving ability during wakefulness.

Testing Relevance

Modern sleep medicine has included testing called a diagnostic polysomnogram, sometimes known as a PSG. This overnight sleep study is typically down at a sleep center or sleep laboratory. The PSG includes measures that are helpful to identify REM sleep, including:

  • Electroencephalography (EEG): Measurement of brain waves
  • Electrooculography (EOG): Measurement of eye movements
  • Electromyography (EMG): Measurement of muscle tone

In REM sleep, the brain waves are very active (appearing much like wakefulness), the eyes move vigorously from side to side or up and down, and the muscle tone of the body is low or absent.

The timing of REM sleep may be important to diagnose specific sleep disorders, including narcolepsy. If there is an abnormal presence of muscle tone during REM sleep, this may substantiate the diagnosis of REM sleep behavior disorder.

Associated Conditions

REM sleep should normally occur at the intervals described above. It may occur early in the presence of sleep deprivation or due to narcolepsy. In fact, the presence of REM sleep in the first 15 minutes of a PSG or during the naps that occur as part of multiple sleep latency (MSLT) testing is consistent with the diagnosis of narcolepsy.

This condition is characterized by unstable sleep-wake states with the intrusion of elements of REM sleep into wakefulness, including:

  • Vivid dream content causing hallucinations during sleep transitions
  • Loss of muscle tone causing cataplexy or sleep paralysis
  • Excessive daytime sleepiness 

This condition may require treatment with medications that stabilize sleep or wakefulness, including the use of sodium oxybate (Xyrem or Xywav) and various stimulants (Provigil, Nuvigil, Ritalin, Adderall, Wakix, etc.), respectively. Sunosi (solriamfetol), a wake-promoting agent, can also be used to improve wakefulness in adults with excessive daytime sleepiness due to narcolepsy.

REM sleep behavior disorder often affects older men and is characterized by dream-enactment behaviors. These may include:

  • Hitting
  • Kicking
  • Talking or screaming
  • Other movements (i.e., shooting a basketball)
  • Falling out of bed
  • Injuries to self or bed partner

These movements and behaviors are possible when the normal loss of muscle tone that occurs in REM is incomplete or absent. Therefore, it becomes possible to act the dream out.

This condition was first described by physicians Mark Mahowald, Carlos Schenck and Scott Bundlie at the Minnesota Regional Sleep Center associated with Hennepin County Medical Center and the University of Minnesota in Minneapolis. 

REM sleep behavior disorder is often managed with safety precautions and with the use of higher doses of melatonin or the prescription medication called clonazepam (or Klonopin).

REM sleep may be a time in the night when obstructive sleep apnea may be more likely to occur in susceptible individuals. This may be associated with frequent or early morning awakenings and secondary insomnia.

Finally, REM sleep may be suppressed by certain antidepressant medications or the use of substances, including alcohol and marijuana.

A Word From Verywell

REM sleep is an important part of a normal night of sleep. It may provide the pleasure of recalled dreams. When there are problems with its regulation or its effects, it may be associated with other sleep disorders, including narcolepsy, REM sleep behavior disorder, and even sleep apnea.

If you feel like you are not sleeping normally, consider an evaluation by a board-certified sleep physician who can arrange for further testing and provide any necessary treatment.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Pelayo R and Dement WC. History of Sleep Physiology and Medicine. Principles and Practice of Sleep Medicine, 6th ed., Philadelphia, Elsevier, 2017, pp. 3-14.

  2. Datta S. Regulation of neuronal activities within REM sleep-sign generatorsSleep. 2009;32(9):1113-1114. doi:10.1093/sleep/32.9.1113

  3. American Academy of Sleep Medicine. International Classification of Sleep Disorders, 3rd ed. Darien, IL: American Academy of Sleep Medicine, 2014.

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.