Establishing cooperation in a mixed-motive social dilemma. An fMRI study investigating the role of social value orientation and dispositional trust.

When people are confronted with social dilemmas, their decision-making strategies tend to be associated with individual social preferences; prosocials have an intrinsic willingness to cooperate, while proselfs need extrinsic motivators signaling personal gain. In this study, the biological roots for the proselfs/prosocials concept are explored by investigating the neural correlates of cooperative versus defect decisions when participants engage in a series of one-shot, anonymous prisoner's dilemma situations. Our data are in line with previous studies showing that prosocials activate several social cognition regions of the brain more than proselfs (here: medial prefrontal cortex, temporo-parietal junction, and precuneus BA 7 (Brodmann area 7), and that dispositional trust positively affects prosocials' decisions to cooperate. At the neural level, however, dispositional trust appears to exert a greater marginal effect on brain activity of proselfs in three social cognition regions, which does not translate into an increase in cooperation. An event-related analysis shows that cooperating prosocials show significantly more activation in the precuneus (BA 7) than proselfs. Based on previous research, we interpret this result to be consistent with prosocials' enhanced tendency to infer the intentions of others in social dilemma games, and the importance of establishing norm congruence when they decide to cooperate.