Impulse entrainment: Computer simulations and studies on the parallel fibers of the cerebellum

The interspike interval for a pair of propagating impulses was studied from a simulation model of axons with a triphasic recovery cycle (relative refractory, supernormal, and subnormal periods) and from electrophysiologic results on the parallel fibers of the cerebellar cortex. Impulse entrainment, whereby convergence of the interspike interval to a fixed value occurs, was predicted from the model for impulses initiated at any point during the recovery cycle. Convergence of the interspike interval toward a fixed value was also observed for the parallel fibers when impulses were initiated during the relative refractory or the early supernormal periods. We suggest that convergence of the interspike interval contributes to regularization of constitutent impulses within a spike train.