The Effects of Oxytocin on Fairness Perception and Related Prosocial Behaviors

Fairness preference is a cornerstone of human sociality, often driving individuals to incur personal costs in order to uphold fairness norms. Oxytocin (OT), a neuropeptide, is considered a potential modulator of prosocial behavior, yet its specific mechanism of action in fairness decision-making remains unclear. Previous research has predominantly focused on the overall effects of OT on behaviors, without differentiating its roles across distinct processing stages such as cognitive evaluation and emotional anticipation. Furthermore, there is a lack of systematic investigation into whether its effects are modulated by social context and gain-loss contexts. Using a randomized, double-blind, placebo-controlled between-subjects design, the present study combines functional magnetic resonance imaging (fMRI) with the Dictator Game (DG) and the Ultimatum Game (UG) to elucidate how intranasal OT influences fairness perception and related prosocial behavior. The UG additionally involves strategic considerations of the proposer arising from the recipient's ability to reject the offer. Participants, act as proposers, are instructed to rate their perceived levels of fairness and guilt when receiving advantageous inequity and fair allocations in both gain and loss contexts. Following ratings, participants make decisions of accepting or rejecting the current allocation. Their brain activity and behavioral responses will be synchronously recorded during the tasks, and scores of questionnaires including Positive and Negative Affect Schedule, State-Trait Anxiety Inventory, Sensitivity to Punishment and Sensitivity to Reward Questionnaire, Social Value Orientation, Self-Report Altruism Scale, Prosocial Tendencies Measure, Behavioral Inhibition System and Behavioral Activation System Scale, Interpersonal Reactivity Index, Toronto Alexithymia Scale, Beck Depression Inventory-Ⅱ, Guilt and Shame Proneness Scale, Test of Self-Conscious Affect are also collected before the experiment.

Inclusion criteria

• Healthy subjects without past or current psychiatric or neurological disorders.

Exclusion criteria

• History of head injury; pregnant, menstruating, taking oral contraceptives; medical or psychiatric illness.
• The presence of metal in the body or claustrophobia.