MATURATION OF THE CONTRALATERALLY RECORDED AUDITORY BRAIN-STEM RESPONSE

Ipsilaterally and contralaterally recorded auditory brain stem responses to 80 dB nHL clicks were recorded from 37 infants, aged 2 weeks to 20 mo and from six adults, all with normal auditory function. With increasing age, contralateral waves, A, B, C, and D and ipsilateral waves III and V decreased in latency, with the contralateral morphology more closely resembling the ipsilateral morphology as age increased, especially after the age of 9 mo. The mean latencies and their change with age for waves A and B resembled those of ipsilateral waves III and III', respectively; both waves C and D demonstrated similarities with wave V. Large waveform changes were seen with maturation in the latency region of contralateral waves C and D. In 42 of 43 subjects, wave V latency occurred after wave C and before wave D. Peak to peak amplitudes of contralateral waves A-B and D-E' increased with age, but were smaller than those of ipsilateral I'-III and V-V', respectively. The smaller contralateral responses make their use for threshold estimation problematic, especially before the age of 9 months. The contralateral response, however, may help to select wave V in ambiguous cases, and to determine response laterality (Ear Hear 12 3: 167-173).