Effect of cooperation level of group on punishment for non-cooperators: a functional magnetic resonance imaging study

Sometimes we punish non-cooperators in our society. Such behavior could be derived from aversive emotion for inequity (inequity aversion) to make non-cooperators cooperative. Thus, punishing behavior derived from inequity is believed to be important for maintaining our society. Meanwhile, our daily experiences suggest that the degree of cooperation by the members of society (cooperation level of the group) could change the punishing behavior for non-cooperators even if the inequity were equal. Such effect of the cooperation level of the group cannot be explained by simple inequity aversion. Although punishment-related brain regions have been reported in previous functional magnetic resonance imaging (fMRI) study, little is known about such regions affected by the cooperation level of the group. In the present fMRI study, we investigated the effect of the cooperation level of the group on the punishing behavior for non-cooperators and its related brain activations by a paradigm in which the degree of the cooperative state varied from low to high. Punishment-related activations were observed in brain regions such as the anterior insula, dorsolateral prefrontal cortex (DLPFC), and anterior cingulate cortex (ACC). The quantity of punishment in a high cooperation context was greater than in a low cooperation context, and activation in the right DLPFC and ACC in a high cooperation context showed greater activity than in a low cooperation context. This indicates that the cooperation level of the group, as well as aversive emotion for inequity, is the important factor of punishing behavior.