Shortly after the first systematic description of the human EEG by Hans Berger in 1928, large individual differences in EEG pattern were noted: when Adrian and Matthews, other pioneers of the EEG research, presented their own EEGs to the members of the Physiological Society in Cambridge in 1934, it was found that Adrian's EEG displayed a regular alpha-rhythm, whereas Matthews produced “no regular waves” (Niedermeyer, 1999). The first twin studies of EEG followed shortly (see Box 1 for the interpretation of twin findings). Based on visual analysis of EEG patterns, Davis & Davis (1936) concluded that the degree of intrapair differences in MZ twins did not exceed the differences between repeated EEG recordings of the same person. In 1958, the first large-scale genetic study of the human EEG (100 MZ and 98DZ pairs) using multiple quantitative variables was published (Vogel, 1958). Using measures such as percent-time alpha and the dominant EEG frequency, Vogel has shown that MZ twin differences on these quantitative measures do not exceed average differences between the right and the left hemisphere of the same person. Because
