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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.


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Fig. 1: 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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