AGE-RELATED ALTERATION IN PROCESSING OF TEMPORAL SOUND FEATURES IN THE AUDITORY MIDBRAIN OF THE CBA MOUSE

The perception of complex sounds, such as speech and animal vocalizati ons, requires the central auditory system to analyze rapid, ongoing fl uctuations in sound frequency and intensity A decline in temporal acui ty has been identified as one component of age-related hearing loss. T he detection of short, silent gaps is thought to reflect an important fundamental dimension of temporal resolution. In this study we compare d the neural response elicited by silent gaps imbedded in noise of sin gle neurons in the inferior colliculus (IC) of young and old CBA mice. IC neurons were classified by their temporal discharge patterns. Phas ic units, which accounted for the majority oi response types encounter ed, tended to have the shortest minimal gap thresholds (MGTs), regardl ess of age. We report three age-related changes in neural processing o f silent gaps. First, although the shortest MGTs (1-2 msec) were obser ved in phasic units from both young and old animals, the number of neu rons exhibiting the shortest MGTs was much lower in old mice, regardle ss of the presentation level. Second, in the majority of phasic units, recovery of response to the stimulus after the silent gap was of a lo wer magnitude and much slower in units from old mice. Finally, the neu ronal map representing response latency versus best frequency was foun d to be altered in the old IC. These results demonstrate a central aud itory system correlate for age-related decline in temporal processing at the level of the auditory midbrain.