LOW-DOSES OF ETHANOL REDUCE EVIDENCE FOR NONLINEAR STRUCTURE IN BRAINACTIVITY

Recent theories of the effects of ethanol on the brain have focused on its direct actions on neuronal membrane proteins. However, neuromolec ular mechanisms whereby ethanol produces its CNS effects in low doses typically used by social drinkers (e.g., 2-3 drinks, 10-25 mM, 0.05-0. 125 gm/dl) remain less well understood. We propose the hypothesis that ethanol may act by introducing a level of randomness or ''noise'' in brain electrical activity. We investigated the hypothesis by applying a battery of tests originally developed for nonlinear time series anal ysis and chaos theory to EEG data collected from 32 men who had partic ipated in an ethanol/placebo challenge protocol. Because nonlinearity is a prerequisite for chaos and because we can detect nonlinearity mor e reliably than chaos, we concentrated on a series of measures that qu antitated different aspects of nonlinearity. For each of these measure s the method of surrogate data was used to assess the significance of evidence for nonlinear structure. Significant nonlinear structure was found in the EEG as evidenced by the measures of time asymmetry, deter minism, and redundancy. In addition, the evidence for nonlinear struct ure in the placebo condition was found to be significantly greater tha n that for ethanol. Nonlinear measures, but not spectral measures, wer e found to correlate with a subject's overall feeling of intoxication. These findings are consistent with the notion that ethanol may act by introducing a level of randomness in neuronal processing as assessed by EEG nonlinear structure.