Time course of adaptation and recovery from adaptation in the cat auditory-nerve neurophonic.

The auditory-nerve neurophonic (ANN) reflects the ensemble response of phase-locked firing in single auditory-nerve fibers to sustained signals. Consequently, neural response properties such as adaptation and recovery from adaptation can be observed. In this study, ANN responses to 800-Hz, 100-ms tones presented at 10-30-dB SL were recorded using bipolar platinum-iridium electrodes placed on the auditory nerve of the cat. The cat ANN adaptation properties were determined and fit to the equation: A(tp) = Yre(-tp/tau Ar) + Yse(-tp/tau As) + Ass. The rapid time constant of adaptation (tau Ar) was invariant across stimulus level, with a mean value of 4.8 (+/- 2.1) ms. The short-term time constant (tau As) decreased approximately 21 ms for each 10-dB increase in probe amplitude. The mean tau As was 116 ms at 10 dB SL, 83.2 ms at 20 dB SL, and 73.5 ms at 30 dB SL. The ANN recovery from adaptation data was analyzed and fit to the equation: A(delta t) = Amax - Yre(-delta t/tau Rr) - Yse(-delta t/tau Rs). Here, tau Rr, the rapid time constant of recovery, and tau Rs, the short-term time constant, were independent of masker intensity in the studied range, with values of 16.2(+/- 9.8) and 125(+/- 50.1) ms, respectively. The results of this study indicate that ANN time constants are comparable to those measured for single units and that the adaptation behavior of phase-locked and nonphase-locked activity appears to be similar.