Abstract
The scientific question we address is how physiological rhythms spontaneously self-regulate. It is fairly widely believed, nowadays, deterministic mechanisms, including perhaps chaos, offer a promising avenue to pursue in answering this question. Complementary to these deterministic foundations, we propose an approach which treats physiologiocal rhythms as fundamentally governed by several random processes, each of which biases the rhythm in different ways. We call this approach stochastic feedback, since it leads naturally to feedback mechanisms that are based on randomness. To illustrate our approach, we treat in some detail the regulation of heart rhythms and sleep-wake transitions during sleep — two classic "unsolved" problems in physiology. We present coherent, physiologically based models and show that a generic process based on the concepts of biased random walk and stochastic feedback can account for a combination of independent scaling characteristics observed in data.