Variability and Chaos: Neurointegrative Principles in Self-Organization of Motor Patterns

Abstract

J R- . 9 U 7 0 5 In this chapter e discuss the possibility that varabiflity may be a central feature of self- organizing prftesses. We suggest that variability may be inherently part of the mechanisms by which adaptive heurocircuits'- emerge, and contrast such functional neurocircuits against definitions involving anatomical or dynamical structures which the self-organizational definition both contains and supercedes. The experimental work focuses on an invertebrate animal, the sea slug, Pleurobranchaea calffornica, which has a rich behavioral repertoire of buccal/oral behaviors, and a relatively simple nervous system containing identifiable neurons. We present evidence from work on a set of 20 neurons, which we refer to as BCNs (buccal-cerebral neurons), that communicate between the buccal ganglion and cerebral ganglion. These neurons are crucial for generating all buccal/oral behaviors, and provide an advantageous source of experimental material for inquiring into the self-organization of group activity. Variability in the activity of the BCNs, and in the motoneurons that they drive, is attributable to low- dimensional chaoseas shown by: 1) autocorrelation functions; 2) correlation analysis of phase portrait dimenSiens; 3) calculation of Lyapunov exponents; and 4) the structure of 1 D maps of Poincar6 sectio7fs: -Xhese findings indicate that some variability may arise from the same mechanisms that generate the patterned activity: i.e., that the observed variations are not noise that is superimposed on the code underlying a behavior., ut rather that they constitute the code itself. We discuss the findings with respect to he role of sensory feedback in the production of adaptive behavior of animals as tley_- interact with complex and often unpredictable environmentsandw-e suggest tha chaotic neural activity provides a means for the nervous system to create nev. informational space rendering animals more stably adaptable in such changing environments., j*/. ,