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An external stimulus or cue, such as daylight or a regularly repeated occurrence, that serves to regulate an organism's biological clock.
zeitgeberA factor in the environment that has periodicity and is capable of synchronising the endogenous circadian rhythm into a 24-hour cycle. Without zeitgebers, the free-running human clock has long been believed to be about 25.3 hours; more recent work by Charles A. Czeisler MD, PhD, pegs the internal human clock at 24 hours and 11 minutes, ±16 minutes.
zeitgeberZeit, German, time, geber, keeper A factor in the environment with a periodicity, capable of synchronizing the endogenous circadian rhythm into a 24-hr cycle; without zeitgebers, the free-running human clock is 25.3 hrs. See Circadian rhythm, Jet lag, Shift work, Sleep disorders. Cf REM sleep.
zeitgeber(tsīt′gā″bĕr, zīt′) [Ger. Zeitgeber, timekeeper]
Any of the mechanisms in nature that keep internal biological clocks synchronized (entrained) with the environment. Zeitgebers can be physical, involving light or temperature (e.g., sunrise, sunset), or social, involving regular activities (e.g., consistent mealtimes).