Alcohol-induced biphasic background and stimulus-elicited EEG changes in relation to blood alcohol levels.

The effects of 0.8 g alcohol kg-1 on CNS processes as reflected in EEG changes were studied in controlled experiments in 14 subjects in relation to BAC levels. A Two Period Change-Over Design with repeated trials over time allowed us to ascertain the time course and to isolate alcohol-induced changes from diurnal variations and effects of sequence and period. Based on spectral analysis of analog EEG recordings, the study has shown differential patterns of bi-phasic or tri-phasic alcohol-induced EEG changes over time in a number of parameters in background and in stimulus-elicited EEG responses varying with the BAC level and the metabolic phase of alcohol biotransformation. An increase in alpha activity during the absorption phase, a shift in the median of the total spectral power to the right (upwards), a decrease in slow activity in the delta and theta bands, and a decrease in variability of the background EEG on one hand and a reduction in stimulus-elicited EEg responses in total spectral alpha, theta and delta bands on the other are all interpreted as a stimulating excitatory effect during the absorption phase, parallel to the increase in BAC. The reverse pattern in the first part of the elimination phase infers a decrease in cerebral activation reflecting the sedative, depressant action of alcohol in this phase. The effects observed in the last trial, to a certain extent interpreted as stimulating, were simultaneous with the beginning of the post-alcohol hangover phase.