REM sleep

REM is short for Rapid Eye Movements. Also known as paradoxical sleep or para-sleep.

In young adults REM sleep occupies about 25% of sleep time. The first episode of REM sleep occurs fairly regularly 80-90 minutes after falling asleep. This time is often shortened in depression.

REM sleep tends to come in ca 5 episodes during the night. They get longer and with shorter intervals as the night passes. It is difficult to awaken a REM-sleeper, quite as difficult as in deep orthodox sleep. On the other hand, spontaneous awakening is relatively frequent.

The EEG in REM sleep is very much like in the awake state, with lots of beta rhythm.

Most dreams, especially the long, interesting ones, occur during REM sleep. When a person is forcibly roused from REM sleep, he will usually report having been interrupted in a dream, which may often be described in some detail. After the REM sleep period is ended, the memory of the dream lapses rapidly. Everybody dreams; those who claim that they do not just never wake up thoroughly enough during REM sleep.

In REM sleep, the general muscle tone is very low; the body is flat out except for the respiratory muscles. There is sporadic muscle twitching and the characteristic rapid, extensive eye movements which give the impression that the sleeper is trying to follow something with the gaze. There is also miosis and erection.

In REM sleep, breathing and pulse tend to be fairly rapid and often irregular.The metabolic rate is not consistently changed up or down, but the normal regulation of temperature is not working and the body becomes poikilothermic. Fortunately, not too much can happen to the body temperature in 30 minutes or so.

Studies of regional brain blood flow indicate that a lot happens, often with episodes of asymmetrical perfusion, but with no obvious pattern. With this and the EEG and the dreaming, it is clear that the brain is very active in REM sleep, but the activity is kept "inside the brain" by strong inhibition of the motor system. In a few, usually elderly persons, this inhibition does not work, and the patient lives out the dreams motorically, with great danger of damage to the patient or bedmate.

The reason why we REM sleep is even less clear than the reason why we sleep at all. If a person is selectively deprived of REM sleep (by awakening every time the characteristic EEG appears) there are few distinctive symptoms, but there will be more REM sleep in the following nights. A "REM sleep centre" cannot be pointed out. 

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Last updated 99 11 18