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EEG Spectral Patterns of Monozygotic Twins

Strong Genetic Control

It is a fact about monozygotic twins that their speaking voices are easily confusible, strikingly similar in pitch and timbre to an extent almost never found in siblings or in dizygotic twins. Now, the tonal qualities of the voice are largely determined by the shape and relative dimensions of the resonant cavities in the head and chest and by the size, musculature and innervation of the vocal cords. We can assume that the variability in most of the relevant components is under strong genetic control, so that twins make their vocal music with nearly identical instruments. The same holds true for brain waves, where we find strikingly similar patterns regardless of whether the co-twins were raised together or reared apart. Specifically, our studies revealed within-pair EEG similarities of the same order of magnitude (r=0.81) as one finds for EEG similarities computed from repeated assessments on the same individual under comparable experimental conditions (r=0.83). This within-pair similarity is contrasted by distinct inter-individual differences which enable nearly unambiguous identification of unrelated persons [Stassen 1988].

Twins Reared Apart

Within the scope of the "Minnesota Twin Study" [Bouchard TJ, Lykken DT, Heston L], monozygotic (MZ) and dizygotic (DZ) twins separated as infants and reared apart were invited to Minneapolis for a full week of study and testing. The mean age at separation was 4 months while the average age at reunion lay around 24 years. Our EEG analysis yielded comparably high within-pair MZ similarities (r=0.80) as in the sample of MZ twins brought up together.

Continuous Phenotype Range

Our results suggested that EEG characteristics possess trait-like qualities which are clearly attributable to genetic predisposition. Heritability estimates, as derived from our twin data, lay in the range of 0.719-0.761 with the DZ/MZ ratio of EEG similarities being very close to the expected value of 0.5, thus supporting a polygenic additive mode of inheritance.

References

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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
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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
EEG spectral pattern

Fig. 12: Pairs of MZ twins brought up together: the upper half shows the EEG spectral pattern of the first co-twin and the lower half the pattern of the second co-twin. Spectral intensities are plotted on log-proportional scales along the vertical axes.
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