Transitioning from childhood into adolescence: A comprehensive longitudinal behavioral and neuroimaging study on prosocial behavior and social inclusion.

Acting prosocially and feeling socially included are important factors for developing social relations. However, little is known about the development of neural trajectories of prosocial behavior and social inclusion in the transition from middle childhood to early adolescence. In this pre-registered study, we investigated the development of prosocial behavior, social inclusion, and their neural mechanisms in a three-wave longitudinal design (ages 7-13 years; N = 512; N = 456; N = 336). We used the Prosocial Cyberball Game, a ball tossing game in which one player is excluded, to measure prosocial compensating behavior. Prosocial compensating behavior showed a linear developmental increase, similar to parent-reported prosocial behavior, whereas parent-reported empathy showed a quadratic trajectory with highest levels in late childhood. On a neural level we found a peak in ventral striatum activity during prosocial compensating behavior. Neural activity during social inclusion showed quadratic age effects in anterior cingulate cortex, insula, striatum, and precuneus, and a linear increase in temporo-parietal junction. Finally, changes in prosocial compensating behavior were negatively associated with changes in ventral striatum and mPFC activity during social inclusion, indicating an important co-occurrence between development in brain and social behavior. Together these findings shed a light on the mechanisms underlying social development from childhood into adolescence.