Genetic aspects of the EEG: an investigation into the within-pair similarity of monozygotic and dizygotic twins with a new method of analysis.

A considerable number of previous studies emphasized the importance of genetic factors in the spontaneous EEG. In this context MZ twins were found to resemble their co-twins as much as they resemble themselves over time, whereas investigations into the within-pair similarity of DZ twins yielded very inconsistent findings. To test these conclusions, we re-analysed the EEGs of an earlier twin study (24 MZ pairs/25 DZ pairs) by means of a new method of analysis. In our study, MZ twins proved to be less like one another than each person is to himself over time. However, this result might be because the EEG data were not optimal for the applied method of analysis, but the existence of true within-pair differences cannot be excluded. Contrary to earlier findings in the literature, the analysis of the EEG of DZ twins showed that, for a sufficiently representative sample, the within-pair similarity is significantly above the inter-individual similarity between unrelated persons.