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EEG Maturation in Monozygotic and Dizygotic Twins

A Longitudinal Study of 200 Twin Pairs

In a large twin-family study comprising EEG recordings of 919 subjects, we applied methods of quantitative genetics to explore the trait-like qualities of EEG parameters, and to quantify the proportions of phentotypic variance that can be attributed to genetic and environmental influences. Our study confirmed previous findings regarding the existence of strong heritable factors that contribute a major proportion to the inter-individual variance in human brain wave patterns. Quantitatively, we found for major EEG parameters a heritability estimate of h^2=0.75 independently derived using two different methods; through an analysis of (a) the parent-offspring EEG similarity and (b) the difference in within-pair EEG similarity between monozygotic and dizygotic twins. The heritability estimates were consistent across the lateral EEG channels, whereas the central channel did not fully fit this picture of overall consistency.

Brain Maturation

Regardless of the many similarities to brain wave patterns of adults, the immature EEG nonetheless exhibits unique characteristics during infancy, childhood and adolescence. These characteristics show distinct inter-individual differences, change continuously over time, and by the age of 20 years they achieve their final form. Since the rhythm of EEG maturation is determined by genetic factors, developmental EEG changes appear to proceed at the same rate for identical twins, whereas the developmental synchronies are much lower within pairs of fraternal twins. Given these empirical findings, we expected that the parent-offspring EEG similarity will continuously increase during adolescence, and that at each stage of development the within-pair EEG similarity of MZ and DZ twins will be in magnitude identical to that of adult twins.

Parent-Offspring Similarity

Our results did not uniformly support these hypotheses. While the within-pair MZ similarity of all EEG parameters under investigation was as high as that of adult twins and the within-pair DZ similarities varied, as expected, from complete similarity (to the extent of being identical twins) to complete dissimilarity (no familial resemblance at all), the parent-offspring EEG similarities were, yet unexpectedly, for the frequency-related EEG parameters as high as those of adult offsprings. Only for the power-related EEG parameters the parent-offspring similarity was found to be significantly lower in the adolescent-offspring sample than in the adult-offspring sample. These findings suggest that the development of brain wave patterns during brain maturation does not uniformly involve all EEG characteristics. For example, the central pacemaker system of alpha frequency, which is hypothesized to be located in the thalamus, does not appear to change its function during adolescence as indicated by the fact that the parent-offspring similarity was identical in the adolescent-offspring and the adult-offspring samples.

References

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Absolute power 7.5-15 Hz

Fig. 29: Distribution of the EEG parameter "absolute power 7.5-15 Hz" in the general population: the figure shows an approximately normal, slightly right-skewed distribution with a mean value of 464.7 and a standard deviation of 157.7 (note that values>600 appear in the right-most bar of the plot). The experimental condition is quiet wakefulness (eyes closed) and the channel is T5-O1.
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