Introduction
CONSTRICTION, DILATION
Oxytocin (OT) has increasingly gathered the interest of cognitive neuroscientists since it was shown to be implicated in social cognition and behavior in humans (The effects of OT on social cognition have been linked to both central and peripherally measured nervous system activity and integrated into hypotheses such as the social salience hypothesis (OT is produced in the paraventricular, supraoptic, and accessory magnocellular nuclei of the hypothalamus (Yet, the characterization of IN-OT’s impact on the ANS function is still unclear, both during cognitive tasks and at rest. So far, IN-OT’s effects on each branch of the ANS have been inconsistent. During tasks, it has been found to (1) increase PNS activity (specifically, indexed by increased HF-HRV) in a facial emotion recognition task, albeit with no effect on the sympathetic nervous system (SNS) measured by electrodermal activity (Pupillary oscillations also reflect ANS activity; however, it has not yet been used to help characterize the effects of IN-OT at rest. The pupil’s constriction is controlled by the sphincter muscle, innervated by the PNS, and its dilation is controlled by the dilator muscle, innervated by the SNS (In sum, the temporal profile of IN-OT’s effect on the ANS at rest remains to be examined, and its impact at a commonly reported time window of assessments of around 40 min is not known. In the present study, we aimed to assess the effect of 24 IU IN-OT on ANS activity at rest, across a large neuroscience experimental session duration, in healthy males, with a double-blind, randomized placebo-controlled cross-over design, recording their pupillary and cardiac activity at one baseline time window pre-administration and at six time windows post-administration (from 15 to 100 min). We examined the effect of IN-OT on proxies of PNS and SNS activity, in each time window, using electrocardiography (ECG) and pupillometry signals: two positive proxies of PNS activity (HF-HRV and PUI) (