It seems likely that this programme enables humans to anticipate and to adapt automatically to the contrasting conditions of their daytime and night-time worlds ( Rusak, 1989). This parallel has obvious functional implications. In this regard, a series of observations in our laboratory led us to propose a specific model for the human circadian system in which two states, one diurnal and one nocturnal, alternate with one another, and in which transitions between the states are switch-like and are separately entrained to dawn and dusk.Īlthough circadian rhythms are generated within the organism and persist in the absence of external input, it is obvious that the temporal programme outlined above mirrors the contours of the external day-night cycle, in effect creating a ‘day within’ ( Pittendrigh, 1988). Many investigators, however, recognize that human circadian rhythms exhibit discontinuous changes and seem to be governed by multiple processes that require more complex models and methods of analysis.
Sometimes, investigators who study human circadian physiology use sine functions to model circadian rhythms, as if they were inherently continuous and sinusoidal.
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