Models of Adolescent Reward Processing. Whereas the adult reward system is fairly well understood, fewer studies have specifically focused on the maturation of the human reward system (X. Xxxxx & Xxxx, 2009; X. X. Xxxxx, et al., 2010). It is suggested that there are differences in how adolescents and adults process rewards and that these differences are associated with risk taking behaviour. Two models have emerged from the literature; both suggest that adolescents use the same underlying brain circuitry to process rewards as adults do. However, the models differ with regards to whether this circuitry is under- (hypo) or over- (hyper) activated during reward processing. Both models focus particularly on activation in the VS, which is a key reward- region that receives dopaminergic afferents from the ventral tegmental area. The first model suggests that the VS is hypoactive and thus less strongly recruited during reward processing in adolescents than it is in adults (Xxxxx, et al., 2004; X. Xxxxx & Xxxx, 2009). According to this model, risk taking is the result of adolescents seeking out risky activities and situations in order to boost the activation in an otherwise sluggish reward system. For the same reason adolescents may be more prone to engage in substance use in order to compensate for the low activation of the reward system. This model is also connected to the Reward Deficiency Hypothesis (Xxxx, Xxxx, et al., 1996), which suggests that risk taking behaviour is the result of reduced activation of the reward system (see Box 1). The opposing model suggests that the reward system of adolescents is hyperactive, meaning that the VS shows increased responsiveness to rewards compared to adults (Xxxxx et al., 2005; Xxxxxx, et al., 2007; Xxxxxx et al., 2006). Studies of dopaminergic function in adolescents also suggest an increase in cortical dopaminergic release during adolescence (Xxxxxxxx, Xxxxxx, & Xxxxxxx, 2003). It is suggested that this increase in VS activation serves an adaptive function as it would increase novelty seeking behaviours that may promote the independence necessary in adulthood. This model is also related to the triadic model, which suggests that adolescent risk taking is the result of interactions between a hyperactive VS combined with limited amygdala activation (mediating harm-avoidance) and prefrontal activation (mediating inhibitory control) (Xxxxx, et al., 2005). Studies that have investigated the development of reward processing suggest that adolescents engage similar n...
