While most of twin EEG studies were conducted in young or middle-aged adult samples, several studies specifically addressed developmental aspects of EEG heritability. van Baal et al. (1996) examined heritability of absolute and relative powers in the main EEG spectral bands in 167 MZ and DZ pairs of 5 year old twins and found very high (80%) heritability for theta, alpha, and beta-1 bands, with somewhat lower heritabilities for delta and beta-2 bands. Another study from the same laboratory found even higher heritabilities (76-89%) of similar spectral EEG parameters in a sample of 16 years old adolescents (van Beijsterveldt et al., 1996). Both studies included opposite-sex DZ twins, which allowed the authors to test for possible differences in heritability between males and females, however, no significant sex differences were observed. One study investigated EEG in infant twins aged 7-12 months and found modest heritabilities and a contribution of shared environmental factors to the main EEG frequency bands; however, heritability tended to increase by the end of the first year of life (Orekhova et al., 2003). In summary, developmental twin studies
