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Recently, ultradian rhythms of arousal lasting approximately 4 hours were attributed to the dopaminergic system in mammals. [5] When the dopaminergic system is perturbed either by use of drugs or by genetic disruption, these 4-hour rhythms can lengthen significantly into the infradian (> 24 h) range, sometimes even lasting for days (> 110 h ...
Empirically, it is an ultradian rhythm of approximately 90 minutes (80–120 minutes [2]) characterized by different levels of excitement and rest. The cycle is mediated by the human biological clock.
A zeitgeber (/ ˈ (t) s aɪ t ɡ eɪ b ər, ˈ z aɪ t-/ (T)SYTE-gay-bər, ZYTE-, German: [ˈtsaɪtˌɡeːbɐ]) is any external or environmental cue that entrains or synchronizes an organism's biological rhythms, usually naturally occurring and serving to entrain to the Earth's 24-hour light/dark and 12-month cycles.
So, siestas and afternoon naps take advantage of this normal rhythm by allowing a person to take a daytime rest when the body is most receptive to its benefits. The current culture of siestas.
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] Within the sleep of adults and infants there are cyclic fluctuations between quiet and active sleep.
Researchers’ suspect that circadian rhythms, which cause cortisol to peak shortly after waking and decrease to its lowest levels around bedtime, play a role in mood patterns. (Getty Images)
Ultradian rhythms, which are cycles shorter than 24 hours, such as the 90-minute REM cycle, the 4-hour nasal cycle, or the 3-hour cycle of growth hormone production. [citation needed] Tidal rhythms, commonly observed in marine life, which follow the roughly 12.4-hour transition from high to low tide and back.
Kleitman made countless additional contributions to the field of sleep research and was especially interested in "rest-activity" cycles, leading to many fundamental findings on circadian and ultradian rhythms. Kleitman proposed the existence of a Basic rest activity cycle, or BRAC, during both sleep and wakefulness. [4] [5]