Rapid eye movement sleep or REM sleep is a phase of sleep where

  • The closed eyes move rapidly and randomly beneath the closed eyelid in a manner to be clearly visible to an observer;
  • The sleeping person lacks muscle tone, such as the ability to remain seated in an upright position; and
  • An EEG exhibits a rapid low-voltage pattern.

polysomnigraph is an instrument that is designed to easily detect these signs without a human observer.  

About 20-25% of overall adult sleep is REM sleep. Typically, a person has about four or five episodes of REM sleep in a typical night's sleep, with the length of REM sleep increasing the longer a person has been asleep (or is closer to waking). The amount of REM sleep decreases as a person ages with infants spending about 80% of their sleep time in REM sleep.

During REM sleep, the brain is much more active than it is during other periods of sleep, being almost as active as when a person is fully conscious. The body's physiology is also quite different than during the rest of sleep - certain neurotransmitters stop working and the body is nearly entirely paralyzed. In addition, it appears that most of the dreams a person remembers happens during this period of sleep.

The purpose of REM sleep is not well understood.  However, it is clear that a person who does not have REM sleep will start to suffer symptoms typical of complete sleep deprivation, such as depression and poor concentration.

Rapid eye movement sleep at Wikipedia

Community content is available under CC-BY-SA unless otherwise noted.