Too Insensitive to Care: Alcohol Increases Human Aggression by Increasing Pain Threshold.

Objective: For thousands of years, people have used alcohol to reduce their sensitivity to physical and emotional pain. Previous research has shown that alcohol increases pain threshold. Previous research has also shown that pain threshold is positively associated with aggression. This research tests the novel hypothesis that the relationship between alcohol and aggression is mediated by increased pain threshold.

Method: To replicate findings, two independent laboratory experiments were conducted (Experiment 1: N=543; Experiment 2: N=327). In both experiments, male and female heavy social drinkers were randomly assigned to consume either an alcohol or a placebo beverage. Next, they reported their pain level to electric shocks that increased in a stepwise manner until the level was described as "painful," which was defined as the pain threshold level. Finally, they delivered painful electric shocks to an ostensible opponent each time they won a competitive reaction time task. Participants won half of the 34 trials (randomly determined). Shock intensity and duration levels were standardized and summed across the 34 trials to create a more comprehensive measure of aggression.

Results: Participants who consumed an alcoholic beverage had a higher pain threshold level than did those who consumed a placebo beverage. The less pain participants felt themselves, the more pain they inflicted on their ostensible partner via electric shock. Results were nearly identical across both experiments.

Conclusions: These findings provide novel evidence regarding one possible reason why intoxicated people behave more aggressively than sober people do. Alcohol intoxication increases aggression partially through its effect on increasing pain threshold.