The social neuroendocrinology of human aggression

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Aggression is a common feature of human life and is expressed to varying degrees in many different social contexts including schools, workplace, highways (i.e., ‘road rage’), athletic venues, and the battlefield. Although aggression can serve important adaptive functions (e.g., competing for valued resources, defending oneself against attack), it may become maladaptive when the intensity, frequency, and duration of the aggressive response is out of proportion to the apparent cause(s). Researchers have long suspected that individual differences in testosterone concentrations may underlie variability in human aggressive behaviour. Despite clear evidence in animal models for the important role of testosterone in promoting aggression, the findings in humans have been relatively weak and inconsistent. Notably, testosterone concentrations are not fixed, but rather, change rapidly in response to social interactions, suggesting that it may be critical to consider context dependent changes in testosterone concentrations when attempting to predict variation in human aggression. Indeed, our research has demonstrated that acute changes in testosterone during competition and/or social provocation are consistently positively correlated with reactive aggression in healthy young men. These findings support the hypothesis that competition- or provocation-induced changes in testosterone may serve to fine-tune ongoing and/or future aggressive behaviour. In the current studies, we propose to extend this work in several important ways. First, we will investigate the extent to which competing with an out-group member (i.e., person of another ethnicity) versus an in-group member influences testosterone reactivity and aggressive behaviour. Second, we will investigate the extent to which self-control influences the relationship between acute changes in testosterone and aggression. Finally, and most importantly, we will use a novel and innovative testosterone administration protocol to investigate the causal role of testosterone in modulating aggressive behaviour in young men. The proposed studies will integrate theory and methodology from social and experimental psychology, neuroendocrinology, and pharmacology toward the ultimate goal of understanding and detailing the basic neuroendocrine mechanisms underlying human aggressive behaviour.