RESONANCE EFFECT FOR NEURAL SPIKE TIME RELIABILITY

The spike timing reliability of Aplysia motoneurons stimulated by repe ated presentation of periodic or aperiodic input currents is investiga ted. Two properties of the input are varied, the frequency content and the relative amplitude of the fluctuations to the mean (expressed as the coefficient of variation; CV). It is shown that, for small relativ e amplitude fluctuations (CV approximate to 0.05-0.15), the reliabilit y of spike timing is enhanced if the input contains a resonant frequen cy equal to the firing rate of the neuron in response to the DC compon ent of the input. This resonance-related enhancement in reliability de creases as the relative amplitude of the fluctuations increases (CV -- > 1). Similar results were obtained for a leaky integrate-and-fire neu ronal model, suggesting that these effects are a general property of e ncoders that combine a threshold with a leaky integrator. These observ ations suggest that, when the magnitude of input fluctuations is small , changes in the power spectrum of the current fluctuations or in the spike discharge rate can have a pronounced effect on the ability of th e neuron to encode a time-varying input with reliably timed spikes.