Spatiotemporal Aspects of Synergetic Processes in the Auditory Cortex as Revealed by the Magnetoencephalogram

Abstract

Synergetics is a discipline concerned with the cooperation of individual parts of a system that produces spatial, temporal, or functional structures (see, e.g., Haken 1977, 1980 a, b). The macroscopic behavior of such a system can change dramatically when certain external parameters are varied. The classical physical example of a synergetic system is the laser, which exhibits quite a number of ordering effects. It was Haken (1977) and Başar (1983) who emphasized the similarity between the behavior of an excited neuronal population and that of a laser when it is pumped: The external stimulus pushes the spontaneous electric activity of the brain — which can be regarded as a set of weakly coupled oscillators — into the coherent state of a single harmonic oscillator, ringing with an intrinsic frequency, for a certain coherence time (“coherence length”), after which fluctuations set in again. Various brain structures were found to have different intrinsic frequencies (Başar 1983). The higher the entropy of the system, i.e., the more independently the individual neurons are firing, the higher is the “excitability” or “response susceptibility” of the neuronal population and vice versa: During a regular firing (state of low entropy), either maintained by stimulation or occurring spontaneously, the neuronal population is less or not at all responsive to a (second) stimulus.