A functional model of the circadian system based on the degree of intercommunication in a complex system

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.