Partners:
Jena, Germany
London, UK
Utrecht, Netherlands
Amsterdam, Netherlands
Barcelona, Spain
Bonn, Germany
Heidelberg, Germany
Szeged, Hungary
Zurich, Switzerland
Marie Curie Action:
035987
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EEG Maturation in Monozygotic and Dizygotic Twins
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.
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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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