Cochlear processes reflected in responses of the cochlear nerve.

The effects of sound frequency, intensity, and duration on responses of cochlear-nerve fibers and inner hair cells (IHCs) are reviewed and compared. The frequency selectivity observed in the nerve is already present in the IHC receptor potential but synaptic transmission appears to influence some other properties of the nerve response. First, the average rate-intensity function of a nerve fiber spans a smaller operating range than the IHC input-output characteristic. However, nerve fibers with different sensitivities can innervate the same IHC and respond over different regions of its characteristic. Second, adaptation is present in the nerve-fiber response but not observed in the IHC. It appears to result from a decrease in synaptic transmission and produces temporal contrast and a decrease in operating range. Interactions among the various effects have important influences on the spatiotemporal pattern of cochlear-nerve responses to complex stimuli.