Moderate alcohol disrupts a mechanism for detection of rare events in human visual cortex.

Moderate doses of alcohol (blood alcohol concentration [BAC] of about 0.05%) may result in acute impairments at various levels of information processing. A number of reports have documented detrimental effects of moderate alcohol on the mismatch negativity (MMN), the electrocortical manifestation of a rapid (100 ms poststimulus) mechanism dedicated to the detection of unexpected auditory change (e.g., Jääskeläinen, et al., 1995). Recently, we and others identified a partial visual counterpart of the MMN, sometimes called the rareness-related negativity (RRN). Analogous to the MMN, the RRN evolves at about 100 ms after the unexpected change and was localized in visual cortex (Kenemans, et al., 2003). Rapid detection of unexpected events is important for everyday-life conditions like driving, prompting the question whether the visual RRN shows sensitivity to moderate alcohol similar to the MMN. In all, 16 subjects were tested either under moderate alcohol or under placebo. Unexpected visual change was implemented by presenting 2.4 versus 0.6 c/d gratings in pseudorandom sequences according to a deviant (10%)/standard (90%) schedule. The alcohol effects on MMN reported before were replicated. Furthermore, the RRN, defined as the difference between deviant and standard event-related potentials between 120 and 170 ms at Oz, was present under placebo but not under alcohol. It is concluded that moderate alcohol does indeed impair the rapid detection in visual cortex of unexpected changes. In contrast, electrocortical correlates of lower level sensory processing were still significantly present under alcohol.