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Brain biological clocks
DOI link for Brain biological clocks
Brain biological clocks book
Brain biological clocks
DOI link for Brain biological clocks
Brain biological clocks book
ABSTRACT
Many body functions vary cyclically with a period of about a day; they have a circadian rhythm. Functions regulated in this way include sleep/wakefulness, core temperature, and the secretion of anterior pituitary hormones. Humans isolated from all external time cues show intrinsic circadian rhythms with a period of about 25 hours initially. This decoupling of circadian rhythms from the normal 24-hour period is called free running and shows that there exist intrinsic circadian clocks that are usually entrained by environmental cues called zeitgebers (German “time-giver”). Zeitgebers include light, exercise, social interactions, and work schedules. Light is the strongest. A powerful light pulse given during subjective night, produces shifts in the circadian rhythm. In humans with normal sleep patterns the nadir in core temperature occurs at about 5 a.m. A light pulse 300given during the night before this time causes circadian rhythms to be delayed (phase delay) whereas a light pulse after this time causes phase advance.