AJP - Regulatory, Integrative and Comparative Physiology, Vol 247, Issue 3 427-R444, Copyright © 1984 by American Physiological Society
Modeling the action of zeitgebers on the human circadian system: comparisons of simulations and data
P. H. Gander, R. E. Kronauer, C. A. Czeisler and M. C. Moore-Ede
In our two-oscillator model for the human circadian timing system, the
effect of an environmental synchronizing cycle (zeitgeber) is determined by
the periods of the two oscillators and of the zeitgeber and by the
zeitgeber strength. The oscillators x and y are postulated to regulate the
core temperature and rest-activity rhythms, respectively. From published
examples of experiments in which human subjects were exposed to artificial
zeitgebers, it is possible to derive estimates of the periods of the core
temperature and/or the rest-activity rhythms and the zeitgeber. Two
strengths of zeitgeber input to the model that correspond to two of the
common zeitgeber regimes used in human entrainment studies have now been
elucidated. Thus specific model simulations can be generated for each of
the available examples of entrainment of human subjects by artificial
zeitgebers. Such simulations indicate that the model can reproduce, with
remarkable subtlety, the types of full and partial entrainment observed
experimentally. The model is thus demonstrated to accommodate the period
and phase control of endogenous rhythms by environmental zeitgebers, which
is a crucial functional attribute of circadian timing systems.
