Abstract
Adolescence is a developmental period characterized by significant increases in the onset of depression, but also by increases in depressive symptoms, even among psychiatrically healthy youth. Disrupted reward function has been postulated as a critical factor in the development of depression, but it is still unclear which adolescents are particularly at risk for rising depressive symptoms. We provide a conceptual stance on gender, pubertal development, and reward type as potential moderators of the association between neural response to reward and rises in depressive symptoms. In addition, we describe preliminary findings that support claims of this conceptual stance. We propose that (1) status-related rewards may be particularly salient for eliciting neural response relevant to depressive symptoms in boys, whereas social rewards may be more salient for eliciting neural response relevant to depressive symptoms in girls and (2) the pattern of reduced striatal response and enhanced medial prefrontal response to reward may be particularly predictive of depressive symptoms in pubertal adolescents. We found that greater vmPFC activation when winning rewards predicted greater increases in depressive symptoms over 2 years, for boys only, and less striatal activation when anticipating rewards predicted greater increases in depressive symptoms over 2 years, for adolescents in mid to late pubertal stages but not those in pre to early puberty. We also propose directions for future studies, including the investigation of social vs. monetary reward directly and the longitudinal assessment of parallel changes in pubertal development, neural response to reward, and depressive symptoms.
Introduction
Rates of depressive episodes rise significantly during adolescence with age 15 found to be the peak age of onset (Lewinsohn et al., 1994) . Not only do many adolescents experience their first depressive episode during this time period, many additional adolescents experience subthreshold rises in depressive symptoms that are nevertheless distressing and interfere with adolescent development (Lewinsohn et al., 2000) . This increase in depressive symptoms during adolescence appears normative in some ways (Sawyer et al., 2009 ) but there are also individual differences in the increase.
Much research has been conducted to delineate risk factors that may contribute to risk for onset of clinical depression during adolescence (Cicchetti and Toth, 1998; Davey et al., 2008; Forbes and Dahl, 2005) . Depression is characterized by a number of symptoms including elevated negative affect and disturbances in sleep and appetite, but it is consistently distinguished from other affective disorders by dysregulation in positive affect and low reward responding (for review, see Forbes and Dahl, 2005) . Accordingly, adolescents with Major Depressive Disorder (MDD) have less striatal response and more ventral medial prefrontal cortex (vmPFC) response to monetary reward (Forbes et al., 2006 (Forbes et al., , 2009 . Similarly, adolescents at risk for MDD (via familial history) also have less striatal response to pleasant stimuli (Monk et al., 2008) and monetary reward (Gotlib et al., 2010) . These findings suggest that reward-related changes may be related to rises in depressive symptoms in youth during adolescence prior to onset of clinical levels of depression.
According to Davey et al.'s (2008) developmental model of depression, social (e.g., greater peer affliation) and neural (e.g., reward circuitry maturation) developmental changes in adolescence result in reward-related changes that may increase risk for depression during this time period. These concurrent neural and social changes during adolescence make pursuit of rewards not only more valued but also more purposeful, leading to increased use of executive function to set and work toward abstract goals involving social rewards (Davey et al., 2008) . As a result, challenges or failures in obtaining dearly-valued social goals (e.g., becoming romantically involved with someone, joining a high-status peer group) can put vulnerable adolescents on a trajectory toward disrupted reward responding and, eventually, depression. Feedback to the developing dopamine system at this sensitive time in development might then lead to disrupted neural reward function and, then, depressive symptoms (Davey et al., 2008) . Neurobiology of Disease 52 (2013) 66-74 

{'paper_id': '4064682', 'title': 'Neural response to reward as a predictor of increases in depressive symptoms in adolescence', 's2_url': 'https://api.semanticscholar.org/CorpusID:4064682', 'source': 'S2ORC'}