NREM sleep

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Non-rapid-eye-movement sleep, in which four progressively deepening stages can be distinguished by EEG measurements: Stage I NREM sleep, without delta waves, is the stage of transition between wakefulness and sleep, and it occupies about 5 per cent of sleeping time in healthy adults; Stage II NREM sleep, with delta waves 20 per cent of the time, is characterized by sleep spindles and K complexes, and it occupies about 50 per cent of normal adult sleeping time; and Stages III and IV NREM sleep, or slow-wave sleep, with delta waves more than 50 per cent of the time, are the deepest levels, and they occupy about 10–20 per cent of normal adult sleeping time. Also called quiet sleep or synchronized (S) sleep. See also sleep. Compare REM sleep.

Subjects: Psychology.

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