Neuroendocrinology of human social behaviour

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According to the General Social Survey conducted by Statistics Canada, 2.2 million violent incidents (including sexual assault, physical assault, and robbery) were reported by Canadian citizens in 2014. Clearly, 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 testosterone (T) may be one of the biological culprits that influences the extent to which people engage in aggressive behaviour. Although baseline levels of T are only weakly associated with human aggression, we have demonstrated that competition- and provocation- induced changes in T reliably predict aggressive behaviour in men, but not women. Furthermore, with the support of an NSERC Discovery Grant (2014-2020) we have developed novel pharmacological challenge paradigms to assess the extent to which T plays a causal role in modulating aggression in men. This research indicated that a single dose of T rapidly increased aggressive behaviour, especially in men with dominant and/or impulsive characteristics.  Finally, we have found that effects of T on aggression depend upon variability in a polymorphic region of the androgen receptor gene.  In the current experiments, we propose to build upon these findings in several important ways. First, we will develop a novel pharmacological challenge protocol to examine the extent to which the aggression-potentiating effects of T are mediated by the androgen receptor. Further, we will development a novel pharmacological challenge paradigm to investigate T's causal role in promoting aggression in women. We will also provide a critical test of the "dual hormone" hypothesis by simultaneously manipulating T and cortisol concentrations and assessing the extent to which these hormones interact to predict variability in human aggression. Finally, we will assess the extent to which T plays a broader role in modulating human mating behaviour. This innovative program of research integrates theory and methodology from social psychology, endocrinology, neuroscience, and pharmacology toward the ultimate goal of detailing the basic neuroendocrine mechanisms guiding individual differences in human aggressive behaviour and mating-related psychology and behaviour.