Transmission of information by the axon: II. The channel capacity

The rate of transmission of information by the axon was analyzed in terms of the information theory. It is concluded that the Poisson rather than the uniform density function is optimal for the maximal rate of transmission in a nervous channel using interval code. If the refractory period is neglected, the information capacity {Mathematical expression} and the optimal mean rate of firing {Mathematical expression} are equal and given by: {Mathematical expression} where N is the variance of the jitter in the interval between the action potential. Under physiological conditions, the channel capacity and the optimal mean rate of firing are limited by both the refractory period and the noise. Figures 1 and 2 allow the calculation of the capacity and the optimal mean firing rate for any given refractory period and "noise" level. The analysis is applicable for neuronal channels in which each stimulus produces a single spike and the noise results from the jitter in either the propagation velocity or the synaptic delay.