Changing one's prosocial behavior after interpersonal synchrony requires a number of processes to take place. Therefore, we ask here, how the prosocial effects of synchronized interpersonal activity are mediated by the human brain. Īlthough interpersonal synchrony seems to be universally important, little is known about the neural basis of this phenomenon. Finally, Kirschner and Tomasello (2010) showed that joint music making facilitates prosocial and cooperative behaviors already among four-year-old children. Similarly, Hove and Risen (2009) found that the degree of synchrony between participant and experimenter in a finger-tapping task correlates with subsequent affiliation ratings. Likewise, Wiltermuth and Health (2009) demonstrated increased cooperation among students after joint singing, compared to no singing or forced “asynchronous” singing. In fact, within a study comparing four different experimental groups of male adults, Anshel and Kipper (1988) showed that the members of the group, that had sung together, cooperated better in a prisoner's dilemma game and scored higher on a questionnaire on trust, than the members of the other groups that had either read a poem collectively, listened to music or watched a film together. One hypothesis claims that music and dance are culturally evolved tools for fostering group cohesion and commitment, thereby increasing prosocial in-group behavior and cooperation. Humans are the only primates that spontaneously synchronize their voices and movements during music making and dancing, a behavior found across all cultures and emerging early in human childhood. By showing an overlap in activated areas during synchronized drumming and monetary reward, our findings suggest that interpersonal synchrony is related to the brain's reward system. In addition, participants collected more pencils to help the experimenter when she had drummed in-synchrony than out-of-synchrony during the manipulation run. The activity in the caudate during experiencing synchronous drumming also predicted the number of pencils the participants later collected to help the synchronous experimenter of the manipulation run. The same area also responded to monetary reward in a localizer task with the same participants.
Results revealed that participants who mastered the novel rhythm easily before scanning showed increased activity in the caudate during synchronous drumming.
After scanning, this experimenter “accidentally” dropped eight pencils, and the number of pencils collected by the participants was used as a measure of prosocial commitment. In the last scanning part, which served as the experimental manipulation for the following prosocial behavioral test, one of the experimenters drummed with one half of the participants in-synchrony and with the other out-of-synchrony. 18 female non-musicians were scanned with functional magnetic resonance imaging while they drummed a rhythm, in alternating blocks, with two different experimenters: one drumming in-synchrony and the other out-of-synchrony relative to the participant.
We hypothesized that areas of the brain associated with the processing of reward would be active when individuals experience synchrony during drumming, and that these reward signals would increase prosocial behavior toward this synchronous drum partner. Why does chanting, drumming or dancing together make people feel united? Here we investigate the neural mechanisms underlying interpersonal synchrony and its subsequent effects on prosocial behavior among synchronized individuals.
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