A model for discharge patterns of primary auditory-nerve fibers.

A model for the synapse between an inner hair cell and afferent fiber is presented. The hair cell is assumed to release 25-100 quantized neurotransmitter packets per sec. Each packet causes an exponentially shaped unitary excitatory postsynaptic potential (EPSP). Any particular afferent fiber is assumed to have a discharge threshold either above or below that of the unitary EPSP. Using any reasonable distribution of threshold values, the model produces a bimodal distribution of spontaneous discharge patterns. The group producing high spontaneous rates (greater than 20/sec) all have discharge thresholds below the unitary EPSP level, while the low-spontaneous group (rates less than 20/sec) all have discharge thresholds above that level. Other physiologically realistic results are obtained from the two groups.