The Effect and Mechanism of taVNS in Modulating Human Social Attention

The Effect and Mechanism of taVNS in Modulating Human 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.

In a placebo-controlled, single-blind, mixed-design experiment, investigators plan to determine whether taVNS modulates human social attention and whether such effects depend on oxytocin (OT) modulation.

Participants will first complete free-viewing and stressful tasks to establish baseline social attention. Consistent with prior studies, participants whose baseline data exceed ±3 SD will be excluded from the study. One week later, eligible participants will complete the Chinese-language versions of several questionnaires prior to intervention: the Behavioral Activation System Scale (BAS), Behavioral Inhibition System Scale (BIS), Trait Anxiety Inventory, State Anxiety Inventory (STAI), Liebowitz Social Anxiety Scale (LSAS), Beck Depression Inventory (BDI), Autism Spectrum Quotient (AQ), Positive and Negative Affect Schedule (PANAS), and Interpersonal Reactivity Index (IRI).

Next, the first saliva sample (T1: 1-2 mL, passive drool) will be collected, followed by 30-min non-invasive taVNS (left, right, or bilateral tragus) or sham (earlobe) intervention. A second saliva sample (T2) will be obtained immediately post-stimulation. Behavioral assessments - including free-viewing paradigms of social and non-social stimuli and a stressful antisaccade paradigm - will begin after T2 collection. Social-attention metrics (response time, errors, fixation duration, fixation counts, etc.) will be recorded using eye-tracking equipment.

Upon completion of the eye-tracking tasks, the third saliva sample (T3: ~20 min post-stimulation) will be collected. Participants will then repeat the State Anxiety and PANAS (mood) questionnaires to evaluate intervention-related changes in anxiety and mood. A fourth saliva sample (T4: ~30 min post-stimulation) will subsequently be obtained.

A mixed-linear model or mixed-model ANOVA, followed by appropriate post-hoc analyses, will be applied to eye-tracking behavioural data and questionnaires scores to evaluate intervention effects.

Investigators hypothesize that taVNS will increase social attention and oxytocin release, that social attention changes will be associated with the magnitude of oxytocin release and that bilateral tragus stimulation will be the most effective

Inclusion Criteria:

Healthy adults

Exclusion Criteria:

• History of past or current neurological/psychiatric disorders;
• Use of psychotropic medications (including nicotine and alcohol)
• Visual impairments
• Baseline data exceeds ±3 SD from mean