The effect of oxytocin on pupil response to naturalistic dynamic facial expressions

The neuropeptide oxytocin (OT) has been found to play an important role in a variety of social behaviours and social cognition in particular. The social salience hypothesis of OT suggests that OT shifts attention towards socially relevant stimuli, which offers an explanation for improvements on social cognition measures following OT administration. Pupil dilation occurs with increasing attentional resource allocation and previous research has found that OT administration led to an increase in pupil diameter in response to social stimuli relative to placebo (PL), thereby suggesting increased social attention. The current study aimed to investigate the effects of OT on pupillary responses to more naturalistic social stimuli in a larger sample. Ninety-four male participants took part in the double-blind, placebo controlled, mixed-design study, in which they self-administered either an OT or PL nasal spray before viewing naturalistic dynamic facial expressions of emotion (happy, sad, fear and anger). Contrary to prediction, there was no effect of OT administration on pupil diameter. The results are discussed in light of the social salience hypothesis and with reference to the methodological differences between studies.