Role of Vagal Stimulation in Social Attention

The objectives of this study are to investigate: 1. whether non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) can enhance human interest in social stimuli in free-viewing and stressful tasks; 2. whether its effect on brain function occurs via modulating endogenous oxytocin release; 3. how the stimulation site and various parameters of taVNS should be set to effectively promote the above-mentioned changes in brain function. The main questions it aims to answer are: 1. Does taVNS facilitate a preference for social relative to non-social stimuli in both free-viewing and stressful tasks? 2. Does taVNS increase peripheral concentrations of the neuropeptide oxytocin, and whether these changes are associated with enhanced social attention? 3. Does taVNS stimulation of the right tragus, left tragus, or bilateral tragus sites produce the strongest effects on oxytocin release and social attention? Investigators will compare the effects of taVNS targeting the left tragus, right tragus, or bilateral tragus with ear-lobe sham stimulation (no vagal activation). Eye-tracking will be used across multiple experimental paradigns. For measurements of oxytocin (OT) and arginine vasopressin (AVP), saliva samples will be collected at baseline, immediately after taVNS, 20 min post-stimulation, and 30 min post-stimulation. Investigators will test whether (a) taVNS facilitates social attention, and (b) its effects are associated with elevated OT and AVP release. Investigators hypothesize that taVNS will enhance social attention and oxytocin release, that changes in social attention will be associated with the magnitude of oxytocin release, and that bilateral tragus stimulation will produce the strongest effects on both social attention and oxytocin release.