THE EFFECT OF SYNCHRONIZED INPUTS AT THE SINGLE NEURON LEVEL

It is commonly assumed that temporal synchronization of excitatory syn aptic inputs onto a single neuron increases its firing rate. We invest igate here the role of synaptic synchronization for the leaky integrat e-and-fire neuron as well as for a biophysically and anatomically deta iled compartmental model of a cortical pyramidal cell. We find that if the number of excitatory inputs, N, is on the same order as the numbe r of fully synchronized inputs necessary to trigger a single action po tential, N-t, synchronization always increases the firing rate (for bo th constant and Poisson-distributed input). However, for large values of N compared to N-t, ''overcrowding'' occurs and temporal synchroniza tion is detrimental to firing frequency. This behavior is caused by th e conflicting influence of the low-pass nature of the passive dendriti c membrane on the one hand and the refractory period on the other. If both temporal synchronization as well as the fraction of synchronized inputs (Murthy and Fetz 1993) is varied, synchronization is only advan tageous if either N or the average input frequency, f(in), are small e nough.