In several forms of abnormal behavior in infants and children, the cause is either uncertain or an unspecified organic brain lesion is assumed to be present. Evoked averaged auditory nerve and brain-stem responses to click stimuli were recorded from groups of normal, autistic, minimal brain dysfunction (MBD) and psychomotor retarded children in order to search for electrophysiological evidence for a brain lesion. Most of the control children were awake and most of the experimental children were in sedated sleep but records were also made from some children while awake and again in the same children when asleep and no change was seen in the response traces. In several of the autistic children there were no electrophysiological responses (indicating a profound hearing loss). In several of the psychomotor retarded children the responses from the region of the inferior colliculus were absent. In the other children in the experimental group, auditory nerve and brain-stem responses were recorded with normal response thresholds but abnormal in other ways: the latency of the auditory nerve response was longer than in the normal children. Also, brain-stem transmission time, measured as the time interval from the negative peak of the auditory nerve response to the positive trough of the response from the inferior colliculus, was shortest in the control group and longest in the MBD group. These results thus present electrophysiological evidence for the existence of an organic brain lesion in these children, at least in the brain-stem regions concerned with auditory function. Together with evidence from other studies, there is support for the conclusion that most of the abnormal behavior seen in these patients is due to a diffuse brain lesion.
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