NREM
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The NREM (non-rapid eye movements) is a sleeping period of a human being without rapid eye movement (REM). During this stage, brain activity decreases and the person becomes completely relaxed. Unlike REM sleep, there is usually little or no eye movement during this stage. Dreaming is rare during NREM sleep, and the muscles are not paralyzed as in REM sleep.
Stages of NREM sleep
NREM sleep is divided into four stages:
- Stage 1 - occurs in the beginning of sleep, with slow eye movements and a 50% reduction in consciousness. People in this stage often believe that they are fully awake.
- Stage 2 - the person is unconscious, though awakened easily. No eye movements occur, and dreaming is very rare during this stage. EEG recordings tend to show characteristic "sleep spindles" and "K-complexes" during this stage.
- Stage 3 - transition between stage 2 and stage 4. Brain activity begins to decrease.
- Stage 4 - the deepest stage of sleep, with very little brain activity. Dreaming is more common in this stage than in other stages of NREM sleep though not as common as in REM sleep. This is also the most common stage in which parasomnias occur.