Abstract

Interpersonal aggression is a significant source of individual and societal distress. For this reason, countless research projects have attempted to identify the biological and psychological determinants of aggressive behaviour. An emerging body of literature suggests that the nonapeptide oxytocin (OT), generally regarded as a facilitator of prosocial behaviours, can instead amplify aggression and hostility under certain contexts. The current dissertation was designed to clarify the association between OT and aggression, by investigating this relation in both animal and human samples. In the first study, we conducted a systematic meta-analysis of genetic OT-knockout animal-model studies. Relative to genetically unmodified controls, OT receptor knockout mice were found to exhibit significantly elevated aggression, across all behavioural paradigms and outcome measures. Other forms of genetic modification were found to be less reliably associated with subsequent aggression, suggesting that prenatal OT exposure plays a critical role in the development of aggressive behaviour in adulthood. Evidence of contextual and individual variability was also observed. In the second study, we investigated the association between exogenous OT administration and a form of cognitive bias that may be predictive of future aggressive behaviours: autobiographical memory retrieval biases. We found that, under placebo, high-aggression participants exhibited greater difficulty retrieving specific memories of positive events. Following OT administration, the retrieval of specific memories for positive cue words was selectively improved in high-aggression individuals. Additionally, such individuals rated the emotional valence of their autobiographical memories less negatively under OT, when compared to placebo. Importantly, these findings were exclusive to memories retrieved within a social context. Recollections produced in a non-social environment were rated less positively following OT administration, exclusively for high-aggression participants. These findings again suggest important individual and contextual variability and highlight the potentially deleterious effects of OT administration in the absence of social contact. Together, these studies indicate that OT does modulate the frequency of aggressive behaviours, as well as the cognitive biases that may precede them. Critically, these data also highlight important developmental, individual, and contextual considerations, which in turn allows us to identify viable targets for future research.