The ground state of cortical feed-forward networks

The occurrence of spatio-temporal spike patterns in the cortex is explained by models of divergent/convergent feed-forward subnetworks-synfire chains. Their excited mode is characterized by spike volleys propagating from one neuron group to the next. We demonstrate the existence of an upper bound for group size: above a critical value synchronous activity develops spontaneously from random fluctuations. Stability of the ground state, in which neurons independently fire at low rates, is lost. Comparison of an analytic rate model with network simulations shows that the transition from the asynchronous into the synchronous regime is driven by an instability in rate dynamics. (C) 2002 Elsevier Science B.V. All rights reserved.