AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 4 1118-R1135, Copyright © 1994 by American Physiological Society
A functional model of the circadian system based on the degree of intercommunication in a complex system
A. Diez-Noguera
Laboratori de Fisiologia, Facultat de Farmacia, Universitat de Barcelona, Spain.
A model of the circadian system is presented. It was developed initially
for rats, but after introducing several modifications, we consider that it
may be extended to many other living systems. It was not the purpose of the
study to develop an oversimplified model of the circadian system but rather
to explore the elements and rules that govern the dynamics of a complex
circadian system, assuming its multioscillatory nature. The formulation of
the model is based on the concept of intercommunication in a population of
autonomous oscillators. Most environmental effects (including rhythm
entrainment) can be simulated with the model simply by controlling the
degree of intercommunication. The model introduces the concept of neutral
elements (probably glial cells in real systems) that shorten or lengthen
the period in response to changes in illumination intensity as a
consequence of their presence. Feedback in the system facilitates the
emergence of split patterns. By defining the oscillatory units to have
similar intrinsic period and a relatively low level of internal coupling,
it is possible to obtain complex circadian patterns, maintaining stable
phases among their components, which resemble ultradian rhythms. A computer
program was developed allowing experimentation with a variety of different
definitions and environmental conditions. Although the computer
implementation of the model has required the formulation of the model in
mathematical terms, the strength of the model (and its functional
properties) lies more in the conceptual definition than in its formal
aspects.
