A twin study of the genetic influences on the electroencephalogram.

Many attempts have been made to relate individual differences in the background electroencephalogram (EEG) to various psychiatric conditions (Glaser, 1963; Hill, 1963; Wilson, 1965) and equivalent investigations have recently been carried out with the averaged evoked response waveform (Shagass and Schwartz, 1961, 1962, 1963, and 1965; Jones et al, 1965; Callaway, Jones, and Donchin, 1970) and the alpha attenuation response (Blum, 1957; Wells and Wolf, 1960; Davidoff and McDonald, 1964; Milstein, Stevens, and Sachdev, 1969). The last two measures represent changes induced in the EEG by stimulation. The main features of the spontaneous EEG show marked between subject variability but a tendency towards consistency and long-term stability within the same individual (Hill, 1963). Similar characteristics have been described for the averaged evoked response waveform (Dustman and Beck, 1963 and 1965) and the alpha attenuation response (Fenton and Scotton, 1967; Milstein et al, 1969). While there is strong presumptive evidence that the interindividual differences in the background EEG are influenced by genetic factors, the exact role of heredity remains unknown (Clarke and Harding, 1969). There have been no previous systematic investigations of the genetic aspects of the alpha attenuation response, but the contribution of heredity to the individual variation in the averaged evoked response is claimed to be substantial (Dustman and Beck, 1965). These findings however remain unconfirmed. In the present study, standardized EEG recordings were obtained from 64 well matched, identical and fraternal twins and measures made of the spontaneous EEG and the alpha attenuation and the averaged evoked responses. By this means, the genetic component of variation of the spontaneous