TEMPORAL FLUCTUATIONS IN BIORHYTHMS: EXPRESSION OF SELF-ORGANIZED CRITICALITY?

Recently, a general organizing principle has been reported connecting 1/f-noise with the self-similar scale-invariant 'fractal' properties in space, hence reflecting two sides of a coin, the so-called self-organized critical stale. The basic idea is that dynamical systems with many degrees of freedom operate persistently far from equilibrium at or near a threshold of stability at the border of chaos. Temporal fluctuations which cannot be explained as consequences of statistically independent random events are found in a variety of physical and biological phenomena. The fluctuations of these systems can be characterized by a power spectrum density S(f) decaying as f(-b) at low frequencies with an exponent b < 1.5. We present a new approach to describe the individual biorhythm of humans using data from a colleague who has kept daily records for two years of his state of well-being applying a fifty-point magnitude category scale. This time series was described as a point process by introducing two discriminating rating levels R for the occurrence of R >= 40 and R <= 10. For b < 1 a new method to estimate the low frequency part of S(f) was applied using counting statistics without applying Fast Fourier Transform. The method applied reliably discriminates these types of fluctuations from a random point process, with b = 0.0. It is very tempting to speculate that the neural mechanisms at various levels of the nervous system underlying the perception of different values of the subjective state of well-being, are expressions of a self-organized critical state.