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After the invention of the EEG, the stages of sleep were determined in 1936 by Harvey and Loomis, the first descriptions of delta and theta waves were made by Walter and Dovey, and REM sleep was discovered in 1953. Sleep apnea was identified in 1965. [2] In 1970, the first clinical sleep laboratory was developed at Stanford. [3]
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 of alternate NREM and REM sleep takes an average of 90 minutes, occurring 4–6 times in a good night's sleep. [17] [22] The American Academy of Sleep Medicine (AASM) divides NREM into three stages: N1, N2, and N3, the last of which is also called delta sleep or slow-wave sleep. [23] The whole period normally proceeds in the ...
Each sleep cycle lasts about 90 to 110 minutes and includes stages that fall into two main phases: non-REM (or NREM) sleep and REM sleep. Non-REM sleep has three sub-stages: light sleep, deep ...
[10]: §9.1–2 263–282 (PGO waves have long been measured directly in cats but not in humans because of constraints on experimentation; however, comparable effects have been observed in humans during "phasic" events which occur during REM sleep, and the existence of similar PGO waves is thus inferred.) [15] These waves occur in clusters ...
Stage 3 was formerly the transition between stage 2 and stage 4 where delta waves, associated with "deep" sleep, began to occur, while delta waves dominated in stage 4. In 2007, these were combined into just stage 3 for all of deep sleep. [7] Dreaming is more common in this stage than in other stages of NREM sleep though not as common as in REM ...
The sleep cycle has proven resistant to systematic alteration by drugs. Although some drugs shorten REM periods, they do not abolish the underlying rhythm. Deliberate REM deprivation shortens the cycle temporarily, as the brain moves into REM sleep more readily (the "REM rebound") in an apparent correction for the deprivation. [13]
Within a few months of postnatal development, there is a marked reduction in percentage of hours spent in REM sleep. By the time the child becomes an adult, he spends about 6–7 hours in NREM sleep and only about an hour in REM sleep. [46] [47] This is true not only of humans, but of many animals dependent on their parents for food. [48]