mCAP br Conflict of interest br Acknowledgements This work

Conflict of interest
Acknowledgements This work was funded by the Deutsche Forschungsgemeinschaft, project SFB TRR-58 C01, and the Department of Child and Adolescent Psychiatry, University Hospital Münster.
Introduction The drive for social acceptance can promote a corresponding fear of rejection that, if extreme, may manifest as social anxiety (Klapwijk et al., 2013). Since prediction error signaling supports learning, altered signaling may contribute to some of the hallmarks of social anxiety disorder. Specifically, altered prediction error signaling could lead to deficient recall of positive past social experiences, which in turn could promote the negative social expectation and interpretation biases that are common to patients with social anxiety (Clark and McManus, 2002; Rapee and Heimberg, 1997). Such deficits may be particularly detrimental during adolescence, a sensitive developmental period that is marked by heightened salience of social acceptance and rejection (Brown and Larson, 2009) and the establishment of complex, peer-focused patterns of behavior and learning (Blakemore, 2008; Crone and Dahl, 2012; Nelson et al., 2005; Steinberg and Morris, 2001). These shifts coincide with peak onset rates of social anxiety, and occur in conjunction with significant changes in mCAP function (Casey et al., 2000; Nelson et al., 2014; Ordaz et al., 2013; Pfeifer et al., 2013; Rubia et al., 2006; Satterthwaite et al., 2013). Adolescence begins with hormonal changes of puberty, followed by the physical expression of pubertal maturation over subsequent years (Grumbach, 2002); its conclusion is culturally constrained by the assumption of adult roles (Blakemore and Mills, 2014). This transition involves acquiring skills needed for peer-based relationships (Blakemore and Mills, 2014), which thereby promotes novel patterns of peer-focused behavior and learning (Blakemore, 2008; Crone and Dahl, 2012; Nelson et al., 2005; Steinberg and Morris, 2001). A Prediction Error (PE) model may explain how brain dysfunction during adolescence, a sensitive period of brain development (Casey et al., 2000; Nelson et al., 2014; Ordaz et al., 2013; Pfeifer et al., 2013; Rubia et al., 2006; Satterthwaite et al., 2013), fosters maladaptive social responding. However, limited research uses PE models to assess adolescent psychopathology. In general, PE models specify that predictions are elicited by cues that precede motivationally-salient outcomes; discrepancies between predicted and actual outcomes result in updated predictions (Pessiglione et al., 2006; Schonberg et al., 2007). PEs associated with unexpectedly positive and negative outcomes, respectively, heighten or diminish activity in the striatum (Schultz et al., 1997), a subcortical structure that guides reward-related behavior and learning (O’doherty, 2004; Yin et al., 2009). Functional connectivity between the striatum and medial prefrontal cortex (mPFC) is implicated in updating both predictions and the value ascribed to outcomes (Haber et al., 2006; O’doherty, 2004). However, such connectivity may reach functional maturity relatively late in development (Forbes and Dahl, 2012; Gogtay et al., 2004; Sowell et al., 2002). In fact, recent studies find PE-related developmental differences in the striatum (Cohen et al., 2010) and/or striatal-mPFC connectivity (van den Bos et al., 2012) as well as evidence of deficient mPFC-based connectivity in youths (Britton et al., 2013; Fitzgerald et al., 2011; Roy et al., 2013). Failure to establish normative striatal-MPFC connectivity during adolescence, when peer acceptance becomes a much more motivationally-salient outcome, may have a negative impact on PE-based social learning. This may be one mechanism that contributes to the particularly high onset rate of adolescent social anxiety disorders. However, the same mechanism may be less critical for maintaining symptoms among anxious adults, who have moved beyond a critical phase of development when behavior may be more easily shaped by social learning.