Research Group 'Psychiatric Genetics', Head: Prof. Dr. Hans H. Stassen

Department of Psychiatry, Psychotherapy and Psychosomatics

Psychiatric Hospital, University of Zurich


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.


Stassen HH, Bomben G, Propping P: Genetic aspects of the EEG: an investigation into the within-pair similarity of monozygotic and dizygotic twins with a new method of analysis. Electroenceph clin Neurophysiol 1987; 66: 489-501
Stassen HH, Lykken DT, Bomben G: The within-pair similarity of twins reared apart. Eur Arch Psychiatr Neurol Sci 1988; 237: 244-252
Stassen HH, Lykken DT, Propping P, Bomben G: Genetic determination of the human EEG (survey of recent results from twins reared together and apart). Human Genetics 1988; 80: 165-176
Stassen HH, Lykken DT, Propping P: Zwillingsuntersuchungen zur Genetik des normalen Elektroenzephalogramms. In: P. Baumann (ed): Biologische Psychiatrie der Gegenwart, Wien: Springer 1993, 139-144
Kaprio J, Buchsbaum M, Gottesman II, Heath A, Körner J, Kringlen E, McGuffin P, Propping P, Rietschel M, Stassen HH: What can twin studies contribute to the understanding of adult psychopathology? In: T.J. Bouchard jr. and P. Propping: Twins as a tool for behavioral genetics. Chichester: John Wiley & Sons, Dahlem Workshop Reports, Life Sciences Research Report 1993; 53: 287-299
Dünki RM, Schmid GB, Scheidegger P, Stassen HH, Bomben G, Propping P: Reliable computer-assisted classification of the EEG: EEG variants in index cases and their first-degree relatives. Am J Med Genetics B 1996; 67,1: 1-8
Stassen HH, Bomben G, Hell D: Familial brain wave patterns: study of a 12 sib family. Psychiat Genetics 1998; 8: 141-153
Stassen HH, Coppola R. Torrey EF, Gottesman II, Kuny S, Rickler KC, Hell D: EEG differences in monozygotic twins discordant and concordant for schizophrenia. Psychophysiology 1999; 36,1: 109-117
Dünki RM, Schmid GB, Stassen HH: Intraindividual specificity and stability of the human EEG: Linear vs. nonlinear approaches. Meth Inform Med 2000; 39: 78-82
Umbricht D, Koller R, Schmid L, Skrabo A, Grübel C, Huber T, Stassen HH: How specific are deficits in mismatch negativity generation to schizophrenia? Biol Psychiatry 2003; 53: 1120-1131
Stassen HH: EEG and evoked potentials. In: D. Cooper (ed) Nature Encyclopedia of the Human Genome. Nature Publishing Group, London 2003; 3: 266-269
Weisbrod M, Hill H, Sauer H, Niethammer R, Guggenbühl S, Stassen HH: Nongenetic pathologic developments of brain-wave patterns in monozygotic twins discordant and concordant for schizophrenia. Am J Med Genetics B 2004; 125: 1-9
Buckelmüller J, Landolt HP, Stassen HH, Achermann P: Trait-like individual differences in the human sleep EEG. Neuroscience 2006; 138: 351-356
Absolute power 7.5-15 Hz

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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