Neuronal interspike time distribution and the estimation of neurophysiological and neuroanatomical parameters

The first three moments of the interspike interval are determined for Poisson excitation of a neuron with exponentially decaying membrane potential and a fixed threshold for action potentials. Analytic calculations are presented for the first and second moments for small threshold to EPSP ratios and a wide range of input frequencies. The coefficient of variation plotted against mean interval reveals maxima and minima which had not been apparent from computer simulations. Numerical methods are employed for higher thresholds and for the third moment. The dependence of mean and standard deviation on threshold is approx-imately exponential at a given input frequency. From experimentally determined histograms of interspike intervals for two spontaneously active cut cochlear nucleus neurons, estimates are made of their membrane time constants, input rates of excitation and threshold to EPSP ratios. The number of connections from cochlear nerve fibers to these neurons is hence deduced. 1