Increased frequency of social interaction is associated with enjoyment enhancement and reward system activation

Positive social interactions contribute to the sense that one's life has meaning. Enjoyment of feelings associated through social interaction motivates humans to build social connections according to their personal preferences. Therefore, we hypothesized that social interaction itself activates the reward system in a manner that depends upon individual interaction preferences. To test this hypothesis, we conducted a functional magnetic resonance imaging (fMRI) study in which 38 participants played a virtual ball-toss game in which the number of ball tosses to the participant was either similar to (normal-frequency condition) or higher than (high-frequency condition) the number of tosses to the other players. Participants reported greater-than-anticipated enjoyment during the high-frequency condition, suggesting that receiving a social reward led to unexpected positive feelings. Consistent with this, the high-frequency condition produced stronger activation in the ventral striatum, which is part of the reward system, and the precuneus, representing positive self-image, which might be translated to social reward. Furthermore, ventral striatal activation covaried with individual participants' preference for interactions with others. These findings suggest that an elevated frequency of social interaction is represented as a social reward, which might motivate individuals to promote social interaction in a manner that is modulated by personal preference.