The Effect Of Oxytocin On Cooperation And Its Brain Mechanism

Cooperation is an important social interactive behavior.Previous studies have found that oxytocin can improve the cooperative activities of individual in joint decisionmaking tasks,such as Prisoner's Dilemma,Public Goods Game and Trust Game.Moreover,such effect can be affected by social context clues(such as familiarity between individuals,in-group and out-group)and individual differences(such as gender and social value orientation).Some researchers have argued that the effect of oxytocin on cooperation in joint decision-making tasks is due to its ability to reduce individuals' anxiety about "betrayal" by their peers.However,the effect of oxytocin on joint action which does not involve trade-offs between individual and group interests remains elusive.Therefore,it is imperative to study the effect of oxytocin on joint action which helps to understand the mechanism by which oxytocin enhances cooperation.In this study,2(condition: oxytocin,placebo)x 2(task: cooperation task,independent task)double-blind within-subject design was conducted to examine the effect of oxytocin on cooperation.Forty college students were recruited,and each of them participated the experiment twice paired with a stranger(another participant).In on experiment,they were given nasal sprays of oxytocin,and in the other experiment,they were given nasal sprays of placebo.In each experiment,participants were required to complete a “Etcha-Sketch” task together with the partner(cooperation task)as well as complete the same task by themselves(independent task/control task).The participants' brain activities in the prefrontal cortex(PFC)and temporoparietal joint(TPJ)were recorded by fNIRS simultaneously during the experiment.The social value orientation of the participants were measured in the experiment.In addition,the evaluation of cooperation performance from each participant were collected after the experiment,including the self-contribution rating,the peer-contribution rating,the tacit understanding ratign and the dominant evaluation.The results showed that(1)the performance of the individual task was significantly higher than that of the cooperative task,but the oxytocin group did not show the improvement of the cooperative performance compared with the placebo group.(2)A significant positive correlation between the cooperative performance and tacit understanding rating was found in the oxytocin group,while a significant positive correlation between the cooperative performance and selfcontribution rating was found in the placebo group.(3)Compared with the independent task,the inter-brain synchronization in the orbitofrontal cortex emerged during the cooperation task,and such inter-brain synchronization was positively correlated with the cooperative performance.(4)Under the oxytocin condition,the brain activity in right superior temporal gyrus emerged during cooperative tasks,and such activity showed interaction effect of condition and task.(5)Under the oxytocin condition,the inter-brain synchronization in dorsolateral prefrontal cortex and central posterior gyrus emerged during the cooperative task,and such inter-brain synchronization showed the interaction effect between condition and task.(6)During the cooperative task,no directional neural coupling was found between dominant roles(leader to follower,follower to leader).Our results show that the effect of oxytocin on joint action is reflected in the subjective evaluation after cooperation.Compared with the placebo condition,participants under the oxytocin condition tend to attribute the cooperative performance to the interaction between the two agencies,which reflects the promoting effect of oxytocin on social bonding.In addition,the inter-brain synchronization can be used as a neural marker to reflect the cooperative performance.The inter-brain synchronization in the orbitofrontal cortex during cooperation reflects the continuous prediction and adjustment of cooperative behaviors by both agencies.The activation of the "social brain" area in the oxytocin condition during cooperation shows an increased willingness of participants to cooperate at the neural level.In this study,the effect of oxytocin on joint action was investigated from the perspective of single-brain and multi-brain mechanisms,providing more evidence for the effects of oxytocin on cooperation and its neural mechanisms.