The electroencephalogram (EEG) as a research tool in human behavior genetics: psychological examinations in healthy males with various inherited EEG variants. III. Interpretation of the results.

Interpretation of the results from psychological examinations of 298 probands with inherited EEG variants requires (1) critical evaluation of previous literature on psychological EEG correlates, (2) knowledge of the main concepts and experimental approaches for elucidating the basic mechanisms of EEG rhythms, (3) discussion of previous attempts to link psychological variation in human populations with corresponding variation in brain function, and (4) interpretation of results from considerations at these three levels with the data from our own study. At the first level (previous psychological studies), comparison with Schmettau's study proved to be especially revealing: Her conclusions about personality correlates with high alpha-index and with "flat" EEGs were very similar to ours with the monotonous alpha- (R) and low-voltage (N) EEGs, respectively. Her EEG type with high beta-index overlaps with our beta-diffuse (BD) type; a tendency to psychasthenia and low resistance to stress is less obvious in our group, but is expressed indirectly by reduced speed and accuracy in tests requiring attentiveness and persistence. The correlation between alpha-frequency and intelligence found in other studies was confirmed by the especially high intelligence scores of our group with occipital fast alpha-variants (BO). At the second and third levels of the discussion (EEG mechanisms; neurophysiological theories), the cooperation of cerebral cortex (EEG battery), thalamus (pacemaker), and ARAS (tonic arousal) is discussed, and the personality typologies of Eysenck and Claridge are mentioned. From this and other evidence, the following hypotheses are discussed: 1) The personality profiles of the R group are influenced by high activity and efficiency of the thalamic alpha-pacemaker(s), which leads to a high degree of modulation, selection, and amplification of afferent stimuli. 2) In the countertype of this EEG variant, the N EEG, a low modulation and amplification by the thalamic alpha-pacemaker is assumed. This leads to relatively low intensity of feeling and to low spontaneous activity, but to faster information processing. Combined with an increased level of tonic arousal in the ARAS, it may cause certain 'neurotic' complaints (our low-voltage borderline (NG) group). 3) The EEG with diffuse beta-waves (BD) is caused by a high level of tonic arousal in the ARAS, which tends to distrub the thalamocortical circuit. This leads to reduced stress resistance and to impairment of intellectual functions, especially space perception. Due to limited evidence, the next two hypotheses are advanced only tentatively: 4) alpha-rhythm with very high frequency 16--19 c/s) leads to improvement of information processing and, hence, to high intellectual performance and motor dexterity. 5) Probands with frontoprecentral beta-groups (BG) show no psychological signs of increased tonic arousal; therefore, these beta-groups are caused not by increased tonic arousal of the ARAS, but by a genetic variant of a thalamic subsystem.