Longitudinal genetic analysis of EEG coherence in young twins

During middle childhood, continuous changes occur in electroencephalogram (EEG) coherence, an index of cortico-cortical connectivity of the brain. In the gradual development of EEG coher-ence, occasional “growth spurts ” are observed which coincide with periods of discontinuous de-velopment in cognition. Discontinuous development may reflect changes in the genetic architec-ture of a trait over time, for instance, by the emergence of new genetic factors. To examine stability and change in genetic and environmental influences on EEG coherence from ages 5 to 7 years, intrahemispheric EEG coherences from 14 connections were collected twice in 209 twin pairs. Overall, heritabilities (h2) were moderate to high for all EEG coherences at both ages (average: 58%). For occipito-cortical connections in the right hemisphere, h2 increased with age due to a decrease in environmental variance. For prefronto-cortical connections in the left hemisphere, h2 decreased with age due to a decrease in genetic variance. New genetic factors at age 7 were found for prefronto-parietal coherence, and centro-occipital and parieto-occipital EEG coherences in both hemispheres and, in the left hemisphere, for prefronto-frontal EEG coherences. Mean genetic cor-relation for these cortico-cortical connections over time was 0.72, indicating that at least part of the genetic influences is age-specific. We argue that this is convincing evidence for the existenc