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While slow waves and sleep spindles are present in stages 2 and 3, stage 2 sleep is characterized by a higher prevalence of spindles, while slow waves dominate the EEG during stage 3. [22] [21] Slow-wave sleep is an active phenomenon probably brought about by the activation of serotonergic neurons of the raphe system. [23]
Polysomnogram demonstrating slow-wave sleep. High amplitude EEG is highlighted in red. Slow-wave sleep (SWS), also known as Stage 3, is characterized by a lack of movement and difficulty of arousal. Slow-wave sleep occurring in both hemispheres is referred to as bihemispheric slow-wave sleep (BSWS) and is common among most animals.
The cause of sleepwalking is unknown. A number of, as yet unproven, hypotheses are suggested for why it might occur, including: delay in the maturity of the central nervous system, [6] increased slow wave sleep, [28] sleep deprivation, fever, and excessive tiredness. There may be a genetic component to sleepwalking.
The optimal nap duration is around 10–20 minutes, as researchers have proven that it takes at least 30 minutes to enter slow-wave sleep, the deepest period of sleep. [46] Napping too long and entering the slow wave cycles can make it difficult to awake from the nap and leave one feeling unrested. This period of drowsiness is called sleep inertia.
NREM sleep can be further classified into NREM stage 1, 2 and 3. The previously considered 4th stage of NREM sleep has been included within stage 3; this stage is also called slow wave sleep (SWS) and is the deepest stage of sleep. [1]
The delta waves have been shown to be generated by recurrent connections within the cerebral cortex. During slow wave sleep, the cortex generates brief periods of activity and inactivity at 0.5–4 Hz, resulting in the generation of the delta waves of slow wave sleep.
NREM parasomnias are arousal disorders that occur during stage 3 (or 4 by the R&K standardization) of NREM sleep—also known as slow wave sleep (SWS). They are caused by a physiological activation in which the patient's brain exits from SWS and is caught in between a sleeping and waking state.
The sleep cycle is an oscillation between the slow-wave and REM (paradoxical) phases of sleep. It is sometimes called the ultradian sleep cycle , sleep–dream cycle , or REM-NREM cycle , to distinguish it from the circadian alternation between sleep and wakefulness .