Impaired gap encoding in aged mouse inferior colliculus at moderate but not high stimulus levels

Age-related deterioration of auditory temporal acuity has been identified as a contributing factor in presbycusis. In the present study, the effects of aging and stimulus level on gap encoding and gap recovery functions were investigated by measuring near-field auditory evoked potentials in the inferior colliculus of eight 3 month old and eight 24 month old CBA/CaJ mice, in response to gap stimuli embedded in broadband noise (40, 60, and 80 dB SPL). Gap encoding was assessed by measuring latencies and amplitudes of peak features of the near-field response, and also with a procedure that calculated the root mean square of the response within specific time windows. The chief differences in gap encoding between young and old mice were longer gap thresholds, slower recovery functions, and longer response peak latencies for old mice at 60, but not 80 dB SPL, although the latency of the earliest measured peak remained delayed for this condition in the old compared with the young mice. These results demonstrate that age-related changes in temporal acuity may interact with stimulus level, and suggest that adequate amplification may be critically important for maintaining temporal acuity with advancing age.