Abbreviation for ‘non-rapid-eye movement sleep’, also referred to as quiet or inactive sleep, and one of the five EEG stages. The period of NREM sleep, taking up about 75% of sleep time and lasting from four to six hours, consists of four such stages (which stages 3 and 4 combined since 2007). Stage 1, occurring at the beginning of sleep and accompanied by slow eye movements, lasts for five to ten minutes as the person falls to sleep. EEG recordings show that the alpha waves of wakefulness disappear and are replaced by theta waves. In the transition from wakefulness to Stage 1 hypnic jerks may be evident. In Stage 2, there are no eye movements, heart and body temperature decrease, and the sleeper can be easily awakened. EEG reveals patterns of sleep spindles and K-complexes. Stage 3/4 is classified as deep or slow-wave sleep, with the typical delta waves now dominating. During this stage dreaming can occur, but is much less than during REM sleep. Dreams during NREM sleep are brief, less likely to involve visual images relative to REM sleep, and subject to forgetting. Up to the age of about 6 months, infants begin sleep with a period of REM sleep, but after this age the onset of sleep assumes the adult form with NREMs.
See Active sleep, Behavioral state, Electroencephalography (EEG), EEG stage 1 sleep, REM sleep, Sleep-wake cycle, Wakefulenss