Prior research suggests that adolescents are drawn to the temptations of immediate rewards to a greater degree than adults, particularly when making decisions in the company of their peers. Dual-systems models of adolescent decision making posit that this immediate reward bias derives from a developmentally normative imbalance in the neural dynamics characterizing the adolescent brain. At a time when the brain’s “top-down” cognitive control system is still developing the processing efficiency and functional integration thought to support mature self-regulation in adulthood, changes in “bottom-up” dopaminergic functioning imbue adolescents with heightened sensitivity to environmentally salient rewards. The resulting bias toward under-controlled, reward-driven behavior may be further accentuated by the presence of peers, who are hypothesized to prime incentive processing circuitry to respond to opportunities for immediate rewards.

The present study utilized functional magnetic resonance imaging (fMRI) to examine age- and context-related differences between adolescents and adults in neural activity and choice behavior corresponding to the comparative evaluation of sooner-smaller and larger-later rewards in an intertemporal choice task. Half of the participants were scanned in a standard “alone” condition, and half were scanned in a “peer” condition, wherein two same-sex, same-age peers informed the participant that they would be observing task performance from the scanner control room. Although behavioral results did not support the hypothesis that peer presence would accentuate adolescents' bias toward immediate rewards, they confirm that, even when making decisions alone, adolescents are more inclined than adults to sacrifice the added value of a larger future reward in order to receive a smaller reward immediately. Furthermore, fMRI results demonstrate at least three important differences between adolescents and adults in neural activity corresponding to the comparative evaluation of rewards. First, adolescents evince stronger activation than adults in regions implicated in incentive processing (including bilateral caudate), consistent with a bias toward reward-driven behavior. Second, adolescents show stronger functional connectivity between a region in the orbitofrontal cortex (OFC) whose activity is correlated with impulsive choice and a region in the ventromedial prefrontal cortex (vmPFC) shown by prior research to represent the value of decision options. This stronger OFC-vmPFC connectivity among adolescents is consistent with greater affective (OFC) influence on choice valuation and behavior (vmPFC). Finally, adolescents show stronger deactivation of regions implicated in cognitive control (including anterior cingulate and dorsolateral prefrontal cortex) when evaluating rewards with relatively longer delays, consistent with a failure to carefully consider the value of future rewards. Together, results suggest that neurodevelopmental theories of adolescent decision making would be improved by more explicit modeling of age differences in the neural processes underlying evaluation of the temporal properties of rewards.