Abstract

The nonapeptide oxytocin promotes social affiliation in both human and non-human animals. However, the mechanisms underlying this phenomenon require further elucidation. There is increasing evidence that oxytocin is facilitating pro-social behaviour by modulating stress reactivity and social cognitive processes. Two double-blind placebo controlled studies were conducted to further test this theory. Study 1 examined the influence of intranasal oxytocin on the affective and cortisol response to the Yale Interpersonal Stressor (YIPS), a live social-rejection paradigm. Ninety-Six undergraduate students underwent the YIPS, where participants are excluded from two separate conversations by two same-sex confederates. Salivary cortisol levels and mood were repeatedly measured throughout the study. Participants were administered a single dose of intranasal oxytocin (24 I.U.) or placebo prior to beginning the YIPS. The YIPS elicited a significant negative mood response that was more pronounced in females than males. However, no significant cortisol response to the stressor and no sex difference in cortisol reactivity were observed. A significant effect of drug condition on cortisol levels was observed. Participants who were administered oxytocin, relative to placebo, exhibited a decrease in cortisol levels during the YIPS. The study ultimately revealed that oxytocin was effective at reducing cortisol concentrations during an interpersonal challenge.

The aim of study 2 was to investigate the relationship between oxytocin and basic emotional information processing in men and women. Eighty-four participants self-administered 24 I.U. intranasal oxytocin or saline and later completed an assessment of the acoustic startle reflex with varying emotional foregrounds. Oxytocin had no impact on the affective modulation of the startle eyeblink response. Rather, oxytocin significantly diminished the acoustic startle response irrespective of the emotional foreground of pictorial stimuli. The results are consistent with studies showing a dampening effect of intranasal oxytocin on the activation of the amygdala in response to emotional stimuli, and further support oxytocin’s anxiolytic effects on physiological arousal.

Overall, both studies demonstrate that oxytocin modulates the HPA axis during interpersonal challenge, and also the basic startle reflex. It is possible that by dampening these physiological systems, oxytocin is serving to facilitate social approach behaviour.