Maturation of the auditory brain stem response in rhesus monkeys (Macaca mulatta).

To document the maturational changes in the auditory brain stem response (ABR) of the rhesus monkey, longitudinal and cross-sectional data were collected on a panel of 31 animals during the first year of life. Each ABR test consisted of averaging 2048 responses to click stimuli delivered at a rate of 21 clicks/sec and elicited at 60, 40, 20 and 10 dB HL intensities in accordance with procedures described previously. The morphology of the ABR wave form recorded at birth was similar to that at 12 months of age and the latencies of the component waves decreased exponentially over this period. The magnitude of decrease in latency was greatest for wave IV and least for wave I. The regression lines for the log of the latencies of 3 waves on age were computed for 3 animals followed longitudinally and for the cross-sectional data set. The slopes of these regression lines were different among animals, indicating differing rates of maturation. However, these slopes were identical for the component waves of any one animal, suggesting that the rate of maturation was constant over the auditory pathway. These changes were similar in pattern to those reported for human data and suggest that the rhesus monkey may serve as an appropriate model of auditory development in man.