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Study of a 12 Sib FamilyHeredity of Brain Wave PatternsOur interest in the present study of a family consisting of 8 sisters and 4 brothers has a psychiatric background. We conjecture that investigations into the heredity of brain wave patterns may contribute to a better understanding of the complex familial aggregations of psychic illnesses. As compared to psychic illnesses, brain wave patterns exhibit a similar complexity on the trait level but on the other hand, they are "objectively" assessable, i.e. in a raterindependent way and in a standardized experimental setting. We therefore designed this study of a family with 8 sisters and 4 brothers in order to quantify the intrafamilial phenotypic heterogeneity of EEG characteristics and to investigate the question of whether EEG characteristics are quantitative or qualitative traits. To this end, each individual was assessed twice at an interval of 14 days so that the reproducibility of results could be tested and the betweensib differences could be qualified with respect to the stability of the underlying parameters over time. Specifically, we addressed the following questions: (1) To what degree do EEG parameters posses traitlike qualities? (2) Are EEG parameters associated with qualitative or quantitative traits? (3) If quantitative, what is the distribution in the general population: unimodal? normally distributed? (4) Is the betweensib EEG similarity half the withinpair EEG similarity of monozygotic twins? EEG RecordingsOur family sample consisted of 12 healthy sibs (8 sisters, 4 brothers) raised in the same environment and ranging in age between 30 and 48 years. The probands were asked to fill out the "Zurich General Health" (ZGF) questionnaire which comprises 80 items and addresses lifetime consumption behavior, somatic disorders, psychosomatic disturbances and psychic impairment. For each of these probands EEGs were recorded twice at 14day intervals under the condition of quiet wakefulness (eyes closed) using standard 1020 electroencephalic lead placements. Each recording comprised 5 minutes of resting EEG derived from 6 parallel channels (P3O1, P4O2, T3T5, T4T6, T5O1, T6O2). BetweenSib SimilaritiesMost EEG parameters possess distinct traitlike qualities as indicated by a high specificity (informativeness) and by a high stability over time. Accordingly, these parameters were deemed to represent a sound basis for our investigation into the betweensib EEG similarities. Detailed analysis revealed a considerable betweensib variation. For example, with respect to "absolute alphaband power" the 12sib sample was partitioned into 5 subgroups: a subgroup of 3 sibs with parameter values around 180; a subgroup of 5 sibs with parameter values around 280; a subgroup of 2 sibs with parameter values around 380; a subgroup of 1 sib with a parameter value around 480; and a subgroup of 1 sib with a parameter value around 580. In terms of the variation observed in the general population, the variation found in this sib sample lay in the lower part of the distribution of the general population and covered nearly 50% of the total range. And this picture of high withinfamily variation was essentially the same for all parameters under consideration. References

Fig. 3: Similarity between spectral patterns as a function of frequency as derived from a comparison of (a) two very similar and (6) two dissimilar sibs. The spectral resolution is 0.25 Hz and the experimental condition quiet wakefulness with eyes closed. 

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