CHAOS IN NEURONAL NETWORKS WITH BALANCED EXCITATORY AND INHIBITORY ACTIVITY

Neurons in the cortex of behaving animals show temporally irregular sp iking patterns. The origin of this irregularity and its implications f or neural processing are unknown. The hypothesis that the temporal var iability in the firing of a neuron results from an approximate balance between its excitatory and inhibitory inputs was investigated theoret ically, Such a balance emerges naturally in large networks of excitato ry and inhibitory neuronal populations that are sparsely connected by relatively strong synapses. The resulting state is characterized by st rongly chaotic dynamics, even when the external inputs to the network are constant in time. Such a network exhibits a linear response, despi te the highly nonlinear dynamics of single neurons, and reacts to chan ging external stimuli on time scales much smaller than the integration time constant of a single neuron.