Why do we interact with others? Some person might answer that social interaction per se is pleasurable. However, neural mechanisms underlying motivation for social interaction are still unknown. To investigate the neural correlates underlying social interaction, we measured functional magnetic resonance imaging (fMRI) during cyberball paradigm (virtual ball-tossing with other ostensible players). In the experiment, ball-tossing to participants was increased after some ball-tossing blocks. In such situation, they reported that they experienced more pleasant feeling than control task (Simple button-pressing tasks. Difference between the ball-tossing and the button-pressing tasks was only graphical user interface). Furthermore, we found significant activation in the right ventral striatum, part of the reward system, for ball-toss increment. These results suggested that social interaction per se is perceived as social reward. Furthermore, the present study implies that humans have fundamental motivation for social interaction, even without explicit practical reward such as monetary reward.

Funding

This study was partly supported by Grant-in-Aid for Scientific Research (S) no. 21220005 (N.S.), Grant-in-Aid for Scientific Research (A) no. 15H01846 (N.S.), and by Grants-in-Aid for Young Scientists (B) no. 25750407 (H.K.) and no. 15K21602 (S.K.S.) from the Japan Society for the Promotion of Science.