STUDIES ON THE HEREDITARY vs. ENVIRONMENTAL FACTORS IN PSYCHOLOGICAL FUNCTIONS BY THE TWIN METHOD
A STUDY ON THE BRAIN WAVES OF TWINS
1963 Volume 33 Issue 6 Pages 305-317
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1963 Volume 33 Issue 6 Pages 305-317
After years of study on the problem of hereditary and environmental factors in human behavior by the twin method, the writer has reached the conclusion that the psychological functions connected more with the activity of the cerebral cortex are rather influenced by the environmental conditions while those more dependent upon lower parts of the brain are predominantly determined by the hereditary factors. This indicates that the psychological and brain functions are characterized by the functionally corresponding structures of strata, and the writer should like to consider it further as an evidence for the strata theory of personality of K. Gottschaldt. The purpose of the present paper is to give another experimental evidence to the strata hypothesis in terms of the brain waves of twins.
The brain waves in the twins of 26 MZ (or EZ in German) pairs and 19 DZ (or ZZ) pairs were investigated either in the state of rest or under stimulation (i, e., sound of a bell, instruction to open the eyes, light stimulus and mental arithmetic) by the 7 FG-040 EEG recorder and the EA-101 EEG analyzer of the San-ei Sokki Co. Ltd. in Japan. The hereditary and environmetal factors are quantitatively specified by the following three kinds of ratio: (1) the ratio of mean intra-pair differences; H:E=mDd:mDm (or E:U=mDz:mDe), where H is hereditary factor; E, envion-mental factor; mDd, mean of intra-pair differences for DZ and mDm, the same mean for MZ, (2) the ratio of mean square of intra-pair differeneces; (3) the ratio of intra-class correlation coefficients; H:E=(ir-fr):(1-ir), where ir is the intra-class correlation coefficient for MZ; fr, the same coefficient for DZ, the correlation coefficient being computed after R. A. Fischer, i.e., r=NΣi=1(xr-x)(x′-x)/Ns2. The definition of this ratio is after K. J. Holzinger and others who originally used it for inter-class correlation. The writer here applies it to intra-class correlation.
The main results are as follows:
(1) The hereditary factor in EEG in the state of rest differs in its strength from one frequency band to another. It is very strong in the α waves and weak in the β, δ and θ waves.
(2) The three indices of the ratio of hereditary and environmental factors show a parallel relation, particularly in α, β1 and β2. Hence any of these indices may be used as a measure of hereditary factor, if the absolute values of the indices are not always equal. Actually, the ratio of intra-class correlation coefficients is the greatest and the ratio of mean intra-pair differences is the least. Gottschaldt's method, that is, the ratio of mean intra-pair differences, has often been criticized from the theoretical point of view. However, it is simple to compute and may be practically used for a general indication, though the three indices must be taken together into more careful consideration.
(3) The hereditary factor is considerably suppressed under experimental stimulation as compared with that in the state of rest. The rate of suppression is more or less different according to the mode of stimulation and greatest under the instruction to open the eyes.
