Down syndrome individuals fail to habituate cortical evoked potentials.

Small sample cortical evoked potentials in response to repetitive auditory stimuli were recorded from 10 Down syndrome individuals and from 10 nonretarded persons whose initial evoked potential amplitude was equated with that of the Down syndrome subjects in a matched-pairs experimental design. Regression analysis of sequential evoked potential amplitude revealed that the nonretarded subjects showed rapid habituation of their cortical evoked potentials whereas the Down syndrome subjects failed to show habituation. The findings support the concept of a deficit in inhibitory capacity at the fundamental electrophysiological level as a substrate for the behavioral-cognitive impairment characteristic of Down syndrome individuals.