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Sample hypnogram (electroencephalogram of sleep) showing sleep cycles characterized by increasing paradoxical (REM) sleep In the ultradian sleep cycle , an organism alternates between deep sleep (slow, large, synchronized brain waves) and paradoxical sleep (faster, desynchronized waves).
Most of the activity in Stage II is in the 3–6 Hz range. Stage III and IV sleep are defined by the presence of delta frequencies and are often referred to collectively as "slow-wave sleep". Stages I–IV comprise non-REM (or "NREM") sleep. The EEG in REM (rapid eye movement) sleep appears somewhat similar to the awake EEG.
Slow-wave sleep (SWS), often referred to as deep sleep, is the third stage of non-rapid eye movement sleep (NREM), where electroencephalography activity is characterised by slow delta waves. [ 2 ] Slow-wave sleep usually lasts between 70 and 90 minutes, taking place during the first hours of the night. [ 3 ]
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. In humans, this cycle takes 70 to 110 minutes (90 ± 20 minutes). [1]
A K-complex is a waveform that may be seen on an electroencephalogram (EEG).It occurs during stage 2 NREM sleep.It is the "largest event in healthy human EEG". [1] They are more frequent in the first sleep cycles.
During rest following a sleep-deprived state, there is a period of rebound sleep which has longer and deeper episodes of SWS to make up for the lack of sleep. [ 6 ] On a hypnogram, a sleep cycle is usually around 90 minutes and there are four to six cycles of REM/NREM stages that occur during a major period of sleep.
Non-rapid eye movement sleep (NREM), also known as quiescent sleep, is, collectively, sleep stages 1–3, previously known as stages 1–4. Rapid eye movement sleep (REM) is not included. There are distinct electroencephalographic and other characteristics seen in each stage. Unlike REM sleep, there is usually little or no eye movement during ...
REM sleep is decreased during the first half of the sleep period and stage 1 sleep is increased in the second half of the sleep period. [5] Most antidepressants, in particular selective serotonin re-uptake inhibitors (SSRIs), such as citalopram and paroxetine , are potent inhibitors of REM sleep and may also cause a REM rebound on discontinuation.