rather than shared environmental, factors. Because MZ twins reared apart share their genotypes but not environment, their phenotypic resemblance is due solely to their genetic commonality. Consequently, correlation between MZ twins reared apart can serve as a direct estimate of heritability. Another large twin study has yielded highly convergent results, indicating very high heritability of spectral band power (van Beijsterveldt et al., 1996). Collectively, these studies suggest that the stable (trait-like) part of EEG variance is almost entirely determined by genetic factors, with little contribution from the shared environmental factors. Sample sizes tended to increase in subsequent studies, providing more accurate estimates of heritability, and the results were remarkably consistent across studies, pointing to a very high heritability of the resting-state human EEG characteristics. Of different EEG frequency bands, alpha band power (8-13 Hz) tends to yield the highest heritability estimates (Anokhin et al., 2006a; Christian et al., 1996; Lykken et al., 1974; Smit et al., 2006; van Beijsterveldt et al., 1996; Vogel, 1970b). Fig. 2 illustrates intrapair twin correlations with respect to alpha-band power (unpublished data from the author's laboratory).
