The effect of gap-marker spectrum on gap-evoked auditory response from the inferior colliculus and auditory cortex of guinea pigs.

The objective of this study is to verify the effects of gap marker spectrum on gap-evoked auditory responses. The gap-evoked potentials were recorded using electrodes implanted in the inferior colliculus (IC) and auditory cortex (AC) of guinea pigs. The gap markers were noise bursts in four frequency bands (500-8,000 Hz, 500-16,000 Hz, 500-32,000 Hz, and 16,000-32,000 Hz), and were tested at three sound levels. The onset response to the post-gap marker was measured to obtain the gap response threshold, and to establish input-output functions for latency and amplitude. Similar to previous behavioural studies, it was found that the gap-response threshold decreased with increasing marker bandwidth. This change was more significant at the cortical level in which the averaged gap-threshold decreased by approximately 2 ms with the bandwidth change. However, the gap threshold in the high frequency region (16,000-32,000 Hz) was comparable to that of the low frequency region (500-16,000 Hz). These results suggest that the total bandwidth of all auditory channels that are recruited determine the temporal resolution measured in gap-evoked potentials.