[Principles and significance of genetically-induced variability of the normal human EEG]

This review describes the following results of human genetic research on the "normal" human EEG: As shown by comprehensive studies on mono- and dizygotic twins, interindividual variability of the human EEG under "normal" conditions is largely genetically determined. This was mainly shown for the resting EEG, but holds true also for the sleeping EEG, the reaction to ethanol, and for visually and auditory evoked potentials. Some fairly common EEG variants have been described which follow simple Mendelian modes of inheritance. Hence, they must go back to correspondingly simply differences in certain genes and gene-determined proteins. These variants have been useful as model systems for a neurobiologically founded research strategy in behaviour genetics of man. Comparative studies using psychological, neurophysiological (visual and auditory evoked potentials) and biochemical methods revealed group difference especially between carriers of the low-voltage EEG, the EEG with monomorphic alpha-waves and an EEG variant containing, in addition to alpha-waves, numerous diffuse beta-waves. Utilizing concepts from basic research in neurophysiology, they could be explained by corresponding differences in central information processing. Individual differences of EEG reaction are also observed after a controlled ethanol load. They have a genetic basis, too. An especially clearcut reaction of the EEG to alcohol can be seen in individuals with irregular alpha-activity of low amplitude in the resting EEG. Moreover, these persons appear to be especially susceptible for "learning" to become alcohol addicts. Individual variability in maturation during childhood and youth of brain structures responsible for EEG production are also under genetic control. This EEG maturation influences intellectual and psychic maturation.