Discounting and VBM

Abstract

Adolescence is a period of significant development in cognition, behavior, and the brain. Neural development during human adolescence involves highly coordinated and sequenced events, characterized by both progressive and regressive processes. In this study we were interested in the emergence of self-control as indexed by impulsivity, and the malleability to change their own preferences, a trait linked to pro-social behavior. We used a computationally derived measure of impulsivity based on an inter-temporal choice task, to examine how its trajectory over adolescence related to maturational morphological brain changes estimated by voxel based morphometry (VBM). We observed a global decrease in grey matter volume over the course of adolescence. Over and above these changes greater impulsivity as indexed in a higher self-discounting parameter was linked to greater grey matter volume within right dorsomedial prefrontal cortex (DMPFC). Likewise we observed that greater choice stochasticity, indexed by a higher decision-variability parameter (reflecting more "noisy" and "exploratory" choices) was linked to greater grey matter volume within bilateral dorsal striatum. We interpret these findings as suggestive that delay in cortical maturation within impulsivity-related brain areas, possibly linked to sluggish neuronal pruning, is a key mediator of impulsivity. Finally, the ability to shift towards other's behavior was positively correlated to grey matter volume within right dorsolateral prefrontal cortex (DLPFC). At first sight, this result seems to contradict previous findings but it does not; DLPFC undergoes a normal pruning across adolescence, however, the more grey matter participants had at the onset of the puberty, the more malleable were in shifting towards other's behaviour. This finding supports the idea that pro-social traits are developed in childhood.