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

Department of Psychiatry, Psychotherapy and Psychosomatics

Psychiatric Hospital, University of Zurich


Normative Study of 91 Healthy Volunteers

The EEG Trait

In this century, rapid progress in the field of quantitative genetics has deeply influenced our understanding of the development of human individuals within their environments. Today, it is generally accepted that external conditions may induce quantitative differences in the individuals' phenotypic appearance, while the essential and qualitative character of the underlying "traits" remains unchanged, whatever the environment.

Repeated Assessments of the Same Individual

Human brain wave patterns (EEG) represent complex traits as is illustrated by the fact that the inheritance does not follow simple mendelian modes in the great majority of parameters used to quantify EEG characteristics. To decompose the information contained in the human EEG into "trait" and "state" components, we performed a normative study with 138 healthy volunteers (75 males and 63 females with ages between 20 and 35 years) who had been ascertained with the aid of a specifically developed questionnaire comprising 65 somatic, psychiatric and social items. The EEGs of these persons were recorded twice at an interval of 14 days and at a fixed time between 8 and 10 o'clock in the morning, thus excluding variations due to circadiane rhythms. All EEGs were traced under comparable experimental conditions (bipolar leads: P3-O1, P4-O2, T3-T5, T4-T6, T5-O1, T6-O2, and in part of the cases F7-T3, F8-T4). The longterm stability of all extracted "traits" was tested on the basis of a 5-year follow-up on 30 cases (15 males, 15 females).

Static and Dynamic Components

Our results show that EEG trait components explain about 75% and EEG state components (reflecting reactions to or interactions with the immediate environment) about 25% of the observed phenotypic variance. EEG trait variables have an approximately normal distribution in the general population, thus suggesting an oligogenic/polygenic additive background.


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

Repeated assessments on the same individuals at 14-day intervals reveal the stability of most EEG parameters over time. Scatter plots of the parameters "relative power", "centroid", "symmetry" and "peak amplitude" demonstrate large inter-individual differences on the one hand, and an almost perfect reproducibility of the individual quantities at 14-day intervals. The first measurements are plotted along the x-axis (day 1) and the measurements taken 14 days later (day 2) are plotted along the y-axis. The experimental condition is quiet wakefulness (eyes closed) and the channel is T3-T5.
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