Analysis of auditory nerve-brainstem responses (ABR) in neonates and very young infants.

Auditory nerve-brainstem responses (ABR) to click stimuli were recorded in 26 normal infants when they were neonates and again in the same infants when they were 3 months old. The cochlear microphonic potential was also recorded in several of the neonates. The following response parameters were studied: latency and amplitude of the auditory nerve response, amplitude of the brainstem response elicited from the region of the interior colliculus, the ratio of the amplitudes of these two waves and brainstem transmission time (BTT): the time interval between these two responses. It was found that the auditory nerve response is only slightly prolonged in neonates with respect to adults and shortens by a small amount from birth to the age of 3 months. The latency of the auditory nerve response in neonates is only about 0.3 ms longer than in adults. BTT is longest in neonates and shortens significantly in 3-month-old infants.