ASA 125th Meeting Ottawa 1993 May

4aBV6. Neural processing of temporal gaps in the inferior colliculus of the awake young and old CBA mouse.

Joseph P. Walton

Robert D. Frisina

William O'Neill

Otolaryngol. Div. and Dept. of Physiol., Univ. Rochester School of Medicine, Rochester, NY 14642-8629

The ability to detect brief silent intervals or gaps in sound forms one important property of temporal resolution. Psychoacoustical evidence suggests such fundamental processing correlates with more complex perceptions, such as speech perception in noise. Moreover, studies have also implicated deficits in temporal resolution as a possible cause for the difficulties observed in presbycusis. The current study compared neuronal response properties and minimal gap thresholds (MGT) in the young (2--4 month) and old (>24 month) CBA mouse model of presbycusis. The following measures were obtained from over 40 single units in each age group; intensity functions for 100-ms tone and noise bursts, spontaneous rate, Q10 bandwidth, and gap functions. Neural correlates of gap detection were studied by imbedding a silent gap (widths from 0.5 to 20 ms) between two noise bursts presented at 30 dB above unit threshold. MGT was quantified by comparing spike counts in multiple time windows before, during, and after the gap. Comparison between young and old response patterns indicate: (1) PST histograms displayed numerous patterns including; onset, onset-sustained, on-off, primarylike, buildup, and off responses, (2) a wide range of spontaneous rates were encountered from 0 to 60 spikes/s, (3) MGT varied with response type regardless of age, and (4) the lowest MGTs (1--2 ms) observed were found both in young and old animals, but the frequency of occurrence was lower in the older animals. [Work supported by NIH-NIA P01 AG09524-01A1.]