Mechanisms of the cochlear nucleus octopus cell's onset response: synaptic effectiveness and threshold.

Octopus cells are one of the principal cell types in the mammalian posteroventral cochlear nucleus. These cells respond to the onset of a toneburst with a precisely timed spike followed by little, if any, sustained activity. While experimental studies have partially characterized the cell, the mechanisms of this onset response are not well understood. The present study involved a model-based investigation that analyzed the responses of a compartmental model of the octopus cell in terms of synaptic effectiveness and dynamic spike threshold. The simulations demonstrate that properties of the onset response (first-spike latency, temporal precision of the first spike, and sustained firing rate) can be predicted from the values of these cell properties for a wide range of model configurations. These relationships were further analyzed through the development of mathematical expressions for synaptic effectiveness and dynamic spike threshold. This computational analysis resulted in a relatively simple explanation of the onset response, as well as predictions of the responses of octopus cells to nontonal, complex stimuli.