SYNCHRONY IN EXCITATORY NEURAL NETWORKS

Synchronization properties of fully connected networks of identical os cillatory neurons are studied, assuming purely excitatory interactions . We analyze their dependence on the time course of the synaptic inter action and on the response of the neurons to small depolarizations. Tw o types of responses are distinguished. In the first type, neurons alw ays respond to small depolarization by advancing the next spike. In th e second type, an excitatory postsynaptic potential (EPSP) received af ter the refractory period delays the firing of the next spike, while a n EPSP received at a later time advances the firing. For these two typ es of responses we derive general conditions under which excitation de stabilizes in-phase synchrony. We show that excitation is generally de synchronizing for neurons with a response of type I but can be synchro nizing for responses of type II when the synaptic interactions are fas t. These results are illustrated on three models of neurons: the Lapic que integrate-and-fire model, the model of Conner ef al., and the Hodg kin-Huxley model. The latter exhibits a type II response, at variance with the first two models, that have type I responses. We then examine the consequences of these results for large networks, focusing on the states of partial coherence that emerge. Finally, we study the Lapicq ue model and the model of Conner et al. at large coupling and show tha t excitation can be desynchronizing even beyond the weak coupling regi me.