br Conclusion br Acknowledgements SH was supported by a stud

Conclusion
Acknowledgements SH was supported by a studentship from Medical Research Council (Reference: 1242237) and a Scatcherd European Scholarship. BD was supported by a Rhodes scholarship and a Clarendon scholarship. GS was supported by a James S. McDonnell Foundation (Understanding Human Cognition) Scholar Award. The authors would like to thank the schools and teachers that made this study possible and the parents/guardians and youths who participated in this study. We would also like to thank Lena Schliephake for helping with the data collection. The authors declare that they have no conflict of interest.
Introduction Adolescence is often perceived to be a sensitive caspofungin for social and emotional development. Indeed, compared to children, adolescents spend more time interacting with peers, and exhibit greater concern with social status, friendships, and romantic relationships (Brown and Larson, 2009; Furman et al., 2009; Suleiman and Harden, 2016). The behaviors, beliefs, or mere presence of peers have also been shown to influence adolescents at various behavioral and neurobiological levels (Doom et al., 2016; Peake et al., 2013; Shulman et al., 2016). In addition to this period of heightened sensitivity to peers, adolescents may display greater emotional variability than adults (Larson et al., 2014), heightened intensity of emotion, regardless of valence (Silk et al., 2009), and particular difficulty regulating emotions elicited by social stimuli (versus nonsocial; Silvers et al., 2012). Taken together, these concurrent changes during adolescence highlight a significant need to better understand the developmental trajectories of affective processing elicited by peer faces. For the past decade and a half, there has been growing research interest in understanding how these social and affective changes are related to neural development, given that adolescence is also a period of remarkable neural plasticity (Kadosh et al., 2013; Zelazo and Carlson, 2012). Indeed, it is now widely accepted that key regions and networks involved in social cognition, emotional reactivity, and emotion regulation all undergo significant functional development during adolescence (Casey et al., 2008; Pfeifer and Blakemore, 2012; Somerville et al., 2011a). However, the field’s existing models of socio-affective neurodevelopment in adolescence (Nelson et al., 2016, 2005) largely describe which brain regions are implicated in these tasks, rather than more precisely proposing when and how the functioning in these regions change (Pfeifer and Allen, 2016). In comparison, dual systems and imbalance models have been used extensively to explain sensitive periods in adolescent risk behavior, and propose age-based trajectories for sensitivity to rewards and regulatory capacities, as well as describe the relationships between these trajectories (Blakemore and Robbins, 2012; Casey et al., 2016; Shulman et al., 2016). These models have sometimes been applied to understanding affective changes in adolescence (Crone and Dahl, 2012; Pfeifer and Allen, 2012; Somerville et al., 2011a,), but have been less extensively tested in this domain. Therefore, one aim of this study was to explore whether brain functioning elicited by socio-affective stimuli reveals a similar sensitive period of imbalance in our cross-sectional sample (following Giuliani and Pfeifer, 2015; Hare et al., 2008; Somerville et al., 2013); such that neural indices of socio-affective reactivity would exhibit non-linear developmental trajectories, with activity peaking by middle adolescence, and that regulation-related responses would display roughly linear patterns of change across the duration of adolescence. In order to acknowledge the importance of peers for affective and regulatory neurodevelopment in adolescence, the current study used a novel set of dynamic adolescent facial expressions.
Methods