AJP - Regulatory, Integrative and Comparative Physiology, Vol 247, Issue 3 418-R426, Copyright © 1984 by American Physiological Society
Simulating the action of zeitgebers on a coupled two-oscillator model of the human circadian system
P. H. Gander, R. E. Kronauer, C. A. Czeisler and M. C. Moore-Ede
Our two-oscillator model was originally designed to describe the circadian
rhythms of human subjects maintained in temporal isolation. The performance
of this model in response to simulated environmental synchronizing cycles
(zeitgebers) is examined here. Six distinct types of synchronization are
demonstrated between the x oscillator (postulated to regulate the core
temperature rhythm), the y oscillator (postulated to regulate the
rest-activity rhythm), and z (the zeitgeber). Four types of synchronization
are identifiable, if we consider only the periods of the three oscillators.
Both x and y may be synchronized by z; either may synchronize with z while
the other exhibits a different period; or x, y, and z may each show
different periods. Two further classes of synchronization are discernible
when phase criteria are taken into account. When either x or y is on the
verge of desynchronizing from the other two oscillators, it undergoes
periodic phase modulations while retaining the common overall period. The
type of synchronization observed depends on the periods of x, y, and z and
on the strength of the z drive. The effects of modifying each of these
parameters have been systematically investigated by simulation, and model
performance is summarized in terms of range of entrainment "maps." These
constitute extensive sets of predictions about expected patterns of
entrainment of the core temperature and rest-activity rhythms of human
subjects exposed to various environmental zeitgebers. Experimental data are
available against which model predictions can be tested.
