ISOCHRONIC MAPPING OF THE AUDITORY BRAIN-STEM RESPONSE - NORMATIVE RESULTS

Isochronic mapping involves recording multi-channel evoked potentials from scalp electrodes and plotting contours of peak latencies. In this study, auditory brainstem responses were recorded from 20 electrode s ites for left, right and binaural stimulation of each ear of 10 male a nd 10 female, normally hearing, young adults. Analysis of the data sho wed that the stimulus parameters of intensity, polarity and rate had n o significant effect on the maps. On monaural stimulation, wave V was recorded first at the contralateral mastoid and ipsilaterally frontall y and last at the ipsilateral mastoid some 350 mu s later. Binaural st imulation gave a symmetrical map, with wave V recorded first frontally and last at the occiput. In contrast, wave III was recorded first ips ilaterally and frontally and last at the contralateral mastoid. Wave I I was recorded first at the rear of the contralateral mastoid and last forward of the ipsilateral mastoid. Comparisons between these results and human physiological studies are in agreement for waves V and III but do not support the concept of the VIIIth nerve alone as the genera tor for wave II. These results suggest that this technique is a potent ially useful diagnostic tool and his intended to evaluate it by testin g patients with a range of sensory, peripheral-neural and central-neur al pathologies.