AGE-RELATED-CHANGES IN AUDITORY-EVOKED POTENTIALS OF GERBILS .1. RESPONSE AMPLITUDES

Auditory brainstem responses (ABRs) were recorded in young (6-10 month ) and aged (36 month) Mongolian gerbils. For each subject, ABR thresho lds and response amplitudes were measured at octave intervals from 1 t hrough 16 kHz. Data from the young animals served as the baselines for comparison to aged animals which were categorized on the basis of aud itory brainstem response (ABR) thresholds. The aged groups included su bjects with thresholds (a) at the mean of a pool of 50 aged gerbils, ( b) one standard deviation (SD) lower than the mean, (c) one sd higher than the mean, and (d) near normal for young gerbils. The amplitudes o f ABR waveforms for the aged gerbils were reduced compared to the youn g subjects, particularly at high sound pressure levels. This was true even for aged subjects with thresholds similar to those for younger su bjects. The slopes of the amplitude-intensity (I/O) functions were sha llower in all aged subjects compared to young subjects. The results su ggest that ABR amplitudes and I/O slopes decrease as a function of age and that the decreases are not a direct result of loss of auditory se nsitivity. The reductions in ABR amplitudes from aged gerbils presumab ly reflect age-related pathology in the auditory periphery, as previou s studies have shown reductions in amplitudes of the compound action p otential of aged gerbils.