A study of 5-6 year old twins showed significant heritability of inter-electrode EEG coherence, with stronger genetic influences (heritability around 60%) observed for long-distance frontal-parietal and central-parietal connections within the hemispheres, whereas most inter-hemispheric coherences showed lower heritability (Ibatoullina et al., 1994). These findings based on a moderate sample of twins were corroborated in a much larger scale study of 5-years old twins that also reported heritability estimates of 50-60% (van Baal et al., 1998), however, the latter study also found substantial heritability of inter-hemispheric connections. Furthermore, van Baal et al. have followed up their sample to age 7 and found that EEG coherence values changed significantly from age 5 to age 7, and their heritability increased for occipital cortical connections. Longitudinal genetic analysis indicated the emergence of new genetic influences on frontal-parietal coherences, consistent with available evidence for rapid cognitive development during this age period (van Baal et al., 2001). A study from the same group using an adolescent sample of twins (age 16) yielded very similar results, with around 60% of individual differences in inter-electrode coherence explained by genetic factors, except the delta band, where heritabilities were somewhat lower (van Beijsterveldt et al., 1998a).
