AGE-RELATED-CHANGES IN THE COMPOUND ACTION-POTENTIALS OF THE 8TH-NERVE IN GUINEA-PIGS

The eighth nerve compound action potential (CAP) in 95 guinea pigs was measured using click stimuli to investigate age-related changes in th eir neural auditory thresholds. The animals were separated into three groups: group A (n = 43, 86 ears; 2-4 months old); group B (n = 29; 58 ears, 13-15 months old); and group C (n = 23; 46 ears, 23-25 months o ld). With increasing age, a gradual elevation of CAP thresholds was cl early seen among the three groups. The negative peak (N1) latencies of the CAP were prolonged, and the N1 amplitudes of the CAP decreased. T here were significant differences in N1 latencies among the three grou ps and in N1 amplitudes between groups A and B, and between groups A a nd C. However, the rate of decline of the thresholds as well as the in put-output function curves of the CAP varied in some of the oldest ani mals, suggesting that there were some individual differences in degene rative aging processes of the auditory system.