Unitary events in multiple single-neuron spiking activity: 1. Detection and significance

It has been proposed that cortical neurons organize dynamically into functi onal groups (cell assemblies) by the temporal structure of their joint spik ing activity. Here, we describe a novel method to detect conspicuous patter ns of coincident joint spike activity among simultaneously recorded single neurons. The statistical significance of these unitary events of coincident joint spike activity is evaluated by the joint-surprise. The method is tes ted and calibrated on the basis of simulated, stationary spike trains of in dependently firing neurons, into which coincident joint spike events were i nserted under controlled conditions. The sensitivity and specificity of the method are investigated for their dependence on physiological parameters ( firing rate, coincidence precision, coincidence pattern complexity) and tem poral resolution of the analysis. In the companion article in this issue, w e describe an extension of the method, designed to deal with nonstationary firing rates.