The twin design can be a useful tool in pharmacogenetics research, since it permits the detection and estimation of genetic influences on the psycho- and neuropharmacological effects of drugs. However, relatively few studies have investigated genetic influences on EEG changes produced by the administration of psychoactive drugs. Propping et al. (1977) examined individual differences in EEG changes after ethanol ingestion in twins. Acute alcohol produces a significant increase in theta- and alpha-power and decrease in beta-power, suggesting a sedative effect. Importantly, MZ twins showed greater similarity with respect to EEG response to alcohol than DZ twins, suggesting that individual differences in the acute effect of alcohol on the brain are at least partially genetically determined. Furthermore, alcohol-induced changes depended on individual differences in the baseline EEG: individuals with irregular, low amplitude alpha-rhythm showed the largest gain in alpha amplitude, while those with abundant, high amplitude alpha activity showed a blunted EEG response to alcohol. Based on the evidence that “desynchronized”, low-alpha EEG is indicative of higher level of tonic arousal and is prevalent among alcoholics, the authors proposed a model
