脳波の個人差の遺伝性

Heritability of Individual EEG Pattern

　脳波の個人差の遺伝学的基礎を客観的の方法によつて研究するために，11-12才の選択されていない健康なふたごの脳波を，一定の条件下で自動分析装置で記録し，その測定値について統計学的処理を行なつた。まず，ふたごの一人をrandomにとり，17人について分散分析を行なつた結果は，

（1）2台の同一型式の分析装置で記録された量の間に大きいちがいがあつた。

（2）速波には個人差がみとめられた。

（3）ひとりの被験者の左右の中心回転部の間にはまつたく差はなかつた。

（4）1時間程度の使用時間では，分析装置はきわめて安定して働くことが明らかにされた。つぎに，1卵性のふたごと同数の同性の2卵性のふたごをrandomにとつて，heritability（遺伝性または遺伝力）を計算すると，

（5）α波の帯域のheritabilityは，安静時でも，閃光刺激をあたえても，いつもきわめて高かつた。

（6）閉眼安静時に左右の中心回転部をくらべると，優位半球である左は，劣位半球である右より徐波のheritabilityが高く，反対に速波のheritabilityが低かつた。この事実を考察するにあたつて，協同研究者たちの心理実験の結果を引用し，劣位半球では，覚醒時の高次活動が自律的であり，このような場合には個人の遺伝的の特長が表面化すると考えられた。また，

（7）閃光刺激をあたえると，低周波の刺激では速波のheritabilityが大きくなり，また，おのおのの帯域の測定値と全部の帯域の測定値の和との比について計算すると，高周波の刺激では徐波のheritabilityが大きくなることが認められた。

（8）α波のheritabilityは，高周波の閃光刺激をあたえたときの方が，低周波の閃光刺激をあたえたときよりいつも大きく，α波が閃光刺激に対して徐波と同じ態度をとることがみられた。

　For the purpose to investigate hereditary basis of detailed normal EEG patterns, EEG of normal monozygotic and dizygotic twins was analysed by automatic frequency analyser of Walter type. EEG lead from left and right central areas at rest and left central area under photic stimulations was analysed by the apparatus. The age of the twins is 11 or 12 years, and they are nonselected (Table, 1, 2). Both twins of a pair were examined simultaneously, and two sets of analysers were used alternatively (Figure 1). A twin of each pair was selected at random for analyses of variance. First analysis of variance indicated significant variance between recordings by two sets of analyser (Table 4). Second analysis of variance, which was carried out separately for two analysers, indicated significantly high variance among 17 individuals in fast wave ranges (Table 5). There is no significant variance between left and right sides of individuals, and no significant variance among 3 measurements at the same area of individuals. The same number of monozygotic and samesexed dizygotic twin pairs was selected at random for calculation of heritability (Table 3). Two kinds of variates were used for the calculation of heritability : absolute "measurement" in each frequency range (Table, 6, Figure, 2, 3) and the "ratio" of measurement in each frequency range to the sum of measurements of 6 frequency ranges (Table, 7, Figure, 4, 5). It is seen that

　1) heritability in alpha range is always remarkably high at rest as well as under photic stimulations.

　2) At rest heritability in slower ranges of left side is often higher than that of right side, and heritability in faster ranges of left side is often lower than that of right side. This result seems to show that in dominant cerebral hemisphere (all subjects are righthanded) higher nervous activity is functioning more actively than nondominant hemisphere, which is functioning more autonomically, and that individual pattern of autonomically functioning nervous activity is controlled by heredity. The assumption is based upon results of experiments carried out by Takagi, Takuma and Kamitake. Among the results sense of time span of 10 or 30 seconds is highly heritable (Figure 6). Experiment 3 of Figure 7 shows heritability of number of blinking in an unit time while the subjects are given psychological tests. These results seem to indicate that pattern of higher activity is heritable if voluntary control does not modify individual pattern of behavior, and if the higher nervous activity is functioning in terms of autonomic state.

　3) It was also seen that under low frequency photic stimulations heritability in fastest wave range is elevated (Figure 2, 3, 4, 5), and that under high frequency photic stimulations heritability in slower wave ranges is markedly elevated (Figure 4, 5). It was also seen that heritability in alpha wave range under high frequency photic stimulations is always greater than that under low frequency photic stimulations. These results are discussed, and it was felt that the study on greater sample of twins of wider range of age under various experimental conditions is desirable.