A functional imaging study of cooperation in two-person reciprocal exchange

Cooperation between individuals requires the ability to infer each other's mental states to form shared expectations over mutual gains and make cooper ative choices that realize these gains. From evidence that the ability for mental state attribution involves the use of prefrontal cortex, we hypothes ize that this area is involved in integrating theory-of-mind processing wit h cooperative actions. We report data from a functional MRI experiment desi gned to test this hypothesis. Subjects in a scanner played standard two-per son "trust and reciprocity" games with both human and computer counterparts for cash rewards. Behavioral data shows that seven subjects consistently a ttempted cooperation with their human counterpart. Within this group prefro ntal regions are more active when subjects are playing a human than when th ey are playing a computer following a fixed (and known) probabilistic strat egy. Within the group of five noncooperators, there are no significant diff erences in prefrontal activation between computer and human conditions.