The role of oxytocin in human social behaviour

Abstract

Social interactions are a fundamental aspect of human life, and behaviours like resource sharing, group defence, bonding, and support between peers have been associated with the neuropeptide oxytocin. However, some evidence has failed to support oxytocin’s foremost prosocial hypothesis, or that its effects are exclusively social. This stems from a still incomplete knowledge of oxytocin’s role on several central and autonomic psychophysiological correlates of social cognition, and from methodological inconsistencies across studies. This thesis describes four studies aimed to test the effects of intranasal oxytocin (IN-OT) on the central and autonomic psychophysiology. The first study addressed the methodological gap in the literature by describing IN-OT’s temporal profile at rest on pupil size and heart rate variability. The second used eye-gaze to test oxytocin’s role in visual attention. The third study uses pupillometry, eye-gaze’s dwell time and spontaneous eye blink rate during a reinforcement learning task to test two of oxytocin’s currently leading hypotheses for its effects on social cognition. Finally, the last study tested whether women’s sexualization influenced men’s cooperative behaviour and concomitant electroencephalography activity during a social dilemma, and whether IN-OT affected such sexualization bias. The thesis’ results suggest the ideal time-window for future studies aiming to probe the effects of IN-OT on pupillometry and heart rate variability. They also validate the posited effects of oxytocin on salience attribution to social stimuli but only on central psychophysiological correlates, and to rewarding/relevant stimuli mostly on autonomic psychophysiological correlates. Behavior-wise, this thesis’ results further corroborate oxytocin’s associations with prosocial attitudes. Altogether, the thesis confirms a dopamine by oxytocin interplay in humans, but challenges oxytocin’s social specificity. Ultimately, this work may serve as foundation for future research on clinical populations and on the interaction of oxytocin with other neuroendocrinological agents.