A frequency-dependent saturation evident in rate-intensity functions of the chinchilla auditory nerve

The shape of Fate-intensity functions recorded from individual neurons of t he auditory nerve using stimulus frequencies at and below the characteristi c frequency have been both well-characterized and modeled by other research ers. However, previous studies of rats-intensity functions using stimulus f requencies above the characteristic frequency have primarily focused on the slopes of the rising phases of the functions. Hence, they did not determin e whether Pare-intensity functions recorded using stimulus frequencies abov e the characteristic frequency saturate, and, if so, at what firing rates t he saturation occurs. In this study, rate-intensity functions have been obt ained from neurons of the eighth nerve of the chinchilla in response to gat ed, sinusoidal stimuli in order to investigate saturation firing rates for frequencies above the characteristic frequency. For each neuron, rate-inten sity functions were obtained for stimulus intensities up to 90 dB SPL at th e characteristic frequency and at as many frequencies above the characteris tic frequency as time would allow. These data clearly reveal that, for freq uencies above the characteristic frequency, saturation occurs at a rate tha t decreases monotonically as the frequency of stimulation is increased. In addition, an empirical equation is given which summarizes the dependence of saturation on stimulus frequency for the data of this study. (C) 1998 Else vier Science B.V. All rights reserved.