Temporal integration in an anuran auditory nerve

We determined temporal integration in individual auditory nerve fibers of the arboreal frog, Eleutherodactylus coqui by measuring the change in rate threshold to tonal stimulation for tone burst durations from 20 to 450 ms. Temporal integration was quantified in two ways: (1) we calculated the temporal integration time constant of the fiber (tau), and (2) we calculated the shift in threshold per decade increment of the tone stimulus (dB/decade). In some cases, the procedure was repeated using a continuous, broadband noise masker (20-50 dB/Hz). Our results indicate that low frequency fibers (CF less than 0.50 kHz) have the longest mean integration time (274 ms), mid-frequency fibers (0.50 to 1.30 kHz) have the shortest mean integration time (183 ms) and high frequency fibers (CF greater than 1.3 kHz) have an intermediate mean integration time (235 ms). Continuous noise increased the integration times of some, but not all fibers, and caused some fibers which did not display temporal integration to do so. We investigated the possibility that these changes may be caused by a decrease in the slope of the rate-intensity function (measured between +5 and +15 dB re threshold) with the addition of the continuous noise masker. The slope of the rate-intensity function decreased (from 73 spikes/s/dB to 49 spikes/s/dB) with the addition of the continuous noise for those fibers (N = 28) that showed an increase in temporal integration with the addition of noise. However, the slopes of the rate-intensity functions also decreased by 30% for those fibers (N = 8) that did not show increasing temporal integration.