Sensitivity of the cochlear nucleus octopus cell to synaptic and membrane properties: A modeling study

Abstract

Octopus cells of the posteroventral cochlear nucleus precisely fire at the onset of short-duration tone bursts, followed by little sustained activity. While this characteristic onset response has been described in experimental studies, its underlying mechanisms are not completely known. The objective of this study was to investigate these mechanisms through a sensitivity analysis of selected parameters of a compartmental model of the octopus cell. The parameters relate to cell morphology, passive electrical properties, synaptic inputs, and active channels. The modeled responses were used to evaluate the effects of four postulated mechanisms on the onset response: the cell’s small membrane time constant, the cell’s numerous weakly effective excitatory inputs, increases in spike threshold caused by sustained depolarization, and electrical loading of the soma by the dendrites. Simulations indicate that the model’s onset response to tone bursts is an emergent property of multiple cell parameters that is best predicted by the ratio of synaptic conductance density to membrane leakage conductance density and by the level of sustained depolarization during the tone burst.