Interval histograms of period of the electroencephalogram and the reaction time in twins.

Measures of central tendency, dispersion, skewness, and kurtosis of interval histograms of half wavelengths in the electroencephalogram (EEF) and performance on an auditory reaction time (RT) task were compared in seven pairs of male monozygotic twins aged 101-134 months and seven pairs of unrelated boys matched to the twins for age. Interval histograms were formed from measurements of 780 half waves taken from EEGs recorded from the left parietal-occipital derivation while subjects performed the RT task. Except in the case of the dispersion of the EEG distributions,the F ratios of within-pair variance in unrelated pairs to within-pair variance in twins were all statistically significant at the 0.05 level of confidence. Statistically significant intraclass correlations of means, medians, and modes of the histograms were found in the group of monozygotic twins but not in the sample of unrelated subjects. Intraclass correlations for dispersion, skewness, and kurtosis of the histograms and for RT were not significantly different from zero in either the twins or unrelated subjects. EEG findings suggested that the basic frequency of the brain's rhythmic electrical activity may be genetically determined; RT findings were inconclusive.