Cortical evoked potentials in monozygotic twins and unrelated subjects: comparisons of exogenous and endogenous components.

Cortical evoked potentials to auditory stimulation were recorded in six pairs of monozygotic twins and six pairs of unrelated subjects matched for age and sex while they performed a stimulus detection task. The cortical potentials were coherently averaged, and the peak latencies of the exogenous (P1, N1, and P2) and endogenous (N2 and P3) components of the average evoked potential (AEP) were investigated. It was hypothesized that latency of the exogenous components of the AEP would be similar in all matched pairs since the characteristics of these components depend primarily on the physical parameters of the stimulus. As endogenous components appear to be associated with a person's intentions, expectations, and decisions, we expected them to be more alike in twins than in unrelated individuals. Findings were in accord with the hypothesis. Latencies of the exogenous components were closely similar in all pairs of subjects. By contrast, latencies of the endogenous components were significantly (P less than or equal to 0.001) more alike in twins than in unrelated subjects.