Fig. 13.

DNLL inactivation mimicked the relief of inhibition produced by a monaural prepulse. A, Control responses evoked without a prepulse. Signals presented to the ear contralateral to the ICc (the excitatory ear) are shown asunfilled bars, whereas signals presented to the ear ipsilateral to the ICc (the inhibitory ear) are shown as hatched bars. BF tone bursts (30 kHz) presented to only the contralateral (excitatory) ear at 15 dB SPL evoked 39 spikes. Binaural tone bursts, having the same contralateral intensity (15 dB SPL) and an ipsilateral intensity of 25 dB SPL, evoked only six discharges, an 85% suppression. When the DNLL was inactivated, the same binaural signal evoked 30 spikes, a 23% suppression. Thus, inactivating the DNLL relieved ∼62% of the ipsilaterally evoked inhibition. Thediagonal slash marks on the horizontal line indicate that tone alone, binaural, and DNLL inactivation records were each obtained separately and independently.B, Relief from inhibition afforded by a 5.0 msec FM prepulse presented to the ear contralateral to the ICc (the excitatory ear). The FM swept from 40 to 20 kHz. The neuron was unresponsive to the FM signal but responded briskly to the trailing binaural tone bursts. The trailing binaural signal evoked 26 spikes when it followed the prepulse by 10 msec (a 33% suppression). Thus the prepulse relieved ∼52% of the ipsilaterally evoked inhibition, a value close to the 62% relieved by DNLL inactivation. Less relief was achieved when the interval was lengthened to 20 msec, and there was no relief at 30 msec, the longest interval.