Dissociable brain networks involved in development of fairness considerations: understanding intentionality behind unfairness.

In this functional magnetic resonance imaging study, we examined developmental changes in the brain regions involved in reactions to unfair allocations. Previous studies on adults suggested that reactions to unfairness are not only affected by the distribution itself but also by the ascribed intentionality of the proposer. In the current study, we employed the mini Ultimatum Game (Falk, Fehr, & Fischbacher, 2003) to examine responder behavior to unfair offers of varying degrees of intentionality. Sixty-eight participants from four age groups (10-, 13-, 15-, and 20-year-olds) carried out the task while fMRI data were acquired. Participants of all ages showed activation in the bilateral insula and dorsal anterior cingulate cortex (dACC) during rejection of unintentional but acceptance of intentional unfair offers. Rejection of unintentional unfair offers further involved increasing activation with age in the temporoparietal junction and the dorsolateral prefrontal cortex. These findings provide evidence for an early developing insula-dACC network involved in detecting personal norm-violations and gradually increasing involvement of temporal and prefrontal brain regions related to intentionality considerations in social reasoning. The results are discussed in light of recent findings on the development of the adolescent social brain network.