A study involving 20 pairs of monozygotic and 17 pairs of dizygotic twins between the ages of 5 and 6 years was conducted to explore the extent to which electroencephalographic (EEG) coherence is affected by genetic and environmental factors. EEG was recorded by electrodes placed on the scalp at F3, F4, P3, P4, C3, C4, O1, and O2 according to the standard 10/20 system. The active electrodes were referenced to linked earlobes. The frequency band pass was 0-45 Hz. Five 5-s periods of background and orienting response EEG were recorded in a sound-attenuating room. The orienting response (OR) was elicited by a series of pure tones differing in frequency and presented in random sequence. Both genetic and environmental influences were found to affect variability in EEG coherence. Genetic effects were slightly more influential during OR than in the resting state. Environmental factors were the predominant influence on interhemispheric connections. Genetic influences were responsible primarily for coherence variations in long distance, intrahemispheric connections.
