We used affective modulation of the eye-blink component of the startle reflex to examine effects of three levels of alcohol intoxication and a no-intoxication control on emotional responses to pleasant, neutral, and unpleasant pictures. Non-problematic student drinkers (n=101; 48 female) were randomly assigned to intoxication groups. Normal inhibition of startle during exposure to pleasant pictures was intact across groups. In contrast, potentiation of startle during viewing of unpleasant pictures was evident in the no- and low-intoxication groups, compared to the intermediate- and high-intoxication groups, in which it was significantly reduced. This pattern suggests that a direct and selective anxiolytic effect of alcohol can occur at higher levels of intoxication without an analogous impact on response to emotionally positive stimuli at similar levels.
Our meta-analysis examined the impact of specific alcohol placebo procedures on two manipulation checks (participant reports of number of alcohol drinks consumed and subjective intoxication) to determine which procedures produced the smallest effect sizes in comparisons between alcohol and placebo conditions. Databases for the years 1990-2007 yielded 44 studies that met inclusion criteria. These were subjected to detailed coding of procedures pertinent to placebo effectiveness. Alcohol versus placebo condition comparisons generally produced large effect sizes for both manipulation checks, but they were moderated by double-blind procedures and by peak breath-alcohol concentration (BrAC) attained in the alcohol condition. Other procedures moderated only the estimated number of alcohol drinks consumed. Implications for selection and assessment of alcohol placebo manipulations and for interpretability of experiments using them are discussed.
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