Rapid and short-term adaptation in auditory nerve responses.

The peristimulatory adaptation of auditory nerve responses in Mongolian gerbil was studied. Constant-intensity tone bursts were used as stimuli. The time decay of the firing rate following the response peak at stimulus onset was described by fitting two exponentially-decaying components and a constant term to the resulting peri-stimulus-time histograms. The slower (short-term) component had an amplitude which was proportional to the driven-steady-state rate (the portion of the constant term in excess of the spontaneous rate). The short-term time constant was on the order of 60 ms and was independent of intensity. The rapid component grew more quickly with intensity and exhibited a greater dynamic range than did the short-term and steady-state components. The time constant of the rapid component was on the order of 1-10 ms, and decreased with increasing intensity in most units. At a constant intensity above unit threshold, the rapid time constant measured at CF was larger for units with low characteristic frequency (CF) than for units with high CF. These results indicate that as intensity increases, the auditory nerve fiber responds more vigorously and with greater time resolution to the onset of tonal stimuli.