EEG maturation

H.H. Stassen, J. Katsanis, S. Malone, W.G. Iacono

Background

Evidence from numerous investigations, including twin and familiy studies, has suggested that the inter-individual differences of human brain wave patterns (EEG) are predominantly determined by genetic factors [cf. Young et al. 1972; Propping et al. 1980; Stassen 1980; Lykken et al. 1982; Stassen 1985; Vogel 1986; Baier and Dose 1987; Christian et al. 1988; Stassen et al. 1988; Linkowski et al. 1989; Fujiwara et al. 1990; Meshkova 1992; Beijsterveldt and Boomsma 1994).

With regard to EEG maturation, human brain waves show a characteristic pattern of development from infancy and early childhood through adulthood (Surwillo 1975; Matthis et al. 1980; Vogel et al. 1982; Gasser et al. 1988; Alvarez-Almador et al. 1989; Harmony et al. 1990; Marosi et al. 1992). In particular, investigations by Vogel (1958, 1970), based on 110 pairs of monozygotic and of 98 pairs of dizygotic twins, have suggested that genetic factors determine not only the individual EEG, but also the rhythm of EEG maturation. The maturation always seemed to proceed at the same rate for identical twins, whereas substantial discrepancies could be observed within the pairs of fraternal twins. The same picture of development synchronies, together with wide and pervasive individual differences, was found in the pioneering "Louisville Twin Study" which investigated the development of behavioral processes (Wilson 1983). On the other hand, normative data that enable the distinction between "natural" fluctuations of and significant changes from the genetically promoted time course of maturation are currently not available. Such normative data would be of great value in the context of recent findings concerning anatomical abnormalities in the brains of 48 MZ twin pairs concordant and discordant for schizophrenia (Torrey et al. 1994), as it is not yet known whether these abnormalities begin to develop at an early stage of adolescence and whether these abnormalities could be detected through EEG analysis already at this early stage.

Material and methods

Our sample consists of >50 MZ and >150 DZ same sex adolescent twin pairs with 3 repeated assessments at 3-year intervals. Of these probands 5 minutes of resting EEG derived from 3/5 parallel channels will be transferred to Zurich, re-calibrated, plotted, and inspected visually for artifacts (e.g. body movements, eye blinks, muscle potentials, loose electrodes) taking advantage of the many years of the Zurich laboratory expertise. Finally, time-series will be Fourier-transformed, stored in a data bank and re-transferred to Minneapolis. Subsequent analyses are based on the frequency bands 0-3.75 Hz, 3.75-7.5 Hz, 7.5-15 Hz, 15-30 Hz and include the single-valued parameters Absolute power, Relative power, Centroid, Symmetry, Peak amplitude, Peak frequency as well as multivariate spectral patterns which have proven to measure the fine graduations of inter-individual EEG differences together with the intra-individual stability of brain wave patterns over time.

Control group

A study of 30 healthy volunteers (aged 20-35 years) with repeated assessments at 5-year intervals will serve as control group in order to distinguish between "natural" fluctuations and "significant" changes during adolescence. The choice of controls in this age interval is based on the fact that brain maturation is complete at the age of 20, and changes in EEG patterns during the age interval 20-35 years exclusively reflect random fluctuations. In addition to that, we will rely upon our normative data from healthy adults in order to determine the extent to which adolescent EEGs differ from matured EEGs.

Goals

In this project we aim to determine normative data with respect to EEG maturation and developmental synchronies in MZ and DZ twins during adolescence. Due to the large sample size, cross-sectional as well as longitudinal analyses can be expected to yield robust estimates of the "natural" variability of EEG maturation in males and females, as well as of the degree to which EEG maturation is synchronized in MZ twins. Specifically, we will address the following problems:

References

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