Physiological control systems can display reversible transitiions in behavior called bifurcations. These transitions can occur between steady state, periodic and chaotic dynamics. Chaotic behavior is deterministic in origin but highly disordered. Preliminary experimental evidence suggective of chaotic behavior in spontaneous cortical neural activity is described in the Progress Report. It has been suggested that these transitions constitute a common dynamical mechanism for several clinically observed failures of physiological regulation. A specific possibility has motivated this investigation: could a bifurcation be an early event in epileptogenesis? This investigaiton proposes to continue both theoretical and experimental investigations of bifurcations in neural behavior. A continued emphasis will be placed on theoretical work. However, the experimental work that has been initiated will continue and become increasingly important. A number of mathematical models of cellular processes display irregular behavior that qualitatively appears to be chaotic. A quantitative assessment of the models using the techniques of dynamical analysis (correlation dimension, Lyapounov exponents, Kolmogorov entropy) will be completed. Our preliminary studies of single unit recordings produced results that are consistent with chaotic behavior. However, the accuracy of these feasibility studies makes a conclusive characterization impossible. We propose to continue these studies using a more accurate experimental technique. A penicillin-induced acute epileptogenic focus will provide a means of investigating possible relationships between bifurcations and epileptogenic activity. In addition to measures of neural behavior derived from dynamical systems theory, we will include a battery of conventional neurophysiological analysis procedures. Correlations between these techniques will be investigated.
