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.
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).
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.
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.
Distribution of the EEG parameter "relative power 7.5-15 Hz" in the general population: the figure shows an approximately normal, slightly right-skewed distribution with a mean value of 44.4 and a standard deviation of 7.8 (note that values>60 appear in the right-most bar of the plot). The experimental condition is quiet wakefulness (eyes closed) and the channel is T5-O1.
Distribution of the EEG parameter "peak amplitude 7.5-15 Hz" in the general population: the figure shows an approximately normal, slightly left-skewed distribution with a mean value of 42.6 and a standard deviation of 20.6 (note that values>100 appear in the right-most bar of the plot). The experimental condition is quiet wakefulness (eyes closed) and the channel is T5-O1.
Distribution of the EEG parameter "peak frequency 7.5-15 Hz" in the general population: the figure shows an approximately normal, slightly asymmetric distribution with a mean value of 10.3 and a standard deviation of 1.0. The experimental condition is quiet wakefulness (eyes closed) and the channel is T5-O1.
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