Adolescence is a period of normative heightened sensitivity to peer influence. Individual differences in susceptibility to peers is related to individual differences in neural sensitivity, particularly in brain regions that support an increasingly greater orientation toward peers. Despite these empirically-established patterns, the more specific psychosocial and socio-cognitive factors associated with individual differences in neural sensitivity to peer influence are just beginning to gain research attention. Specific features of the factors that contribute to how adolescents process social information can inform understanding of the psychological and neurobiological processes involved in what renders adolescents to be more or less susceptible to peer influences. In this paper, we (1) review the literature about peer, family, and broader contextual influences on sensitivity to peers' positive and negative behaviors, (2) outline components of social information processing theories, and (3) discuss features of these models from the perspectives and social cognitive development and social neuroscience. We identify gaps in the current literature that need to be addressed in order to gain a more comprehensive view of adolescent neural sensitivity to peer influence. We conclude by suggesting how future neuroimaging studies can adopt components of this social information processing model to generate new lines of research.

Young adults are acutely sensitive to peer influences. Differences have been found in neural sensitivity to explicit peer influences, such as seeing peer ratings on social media. The present study aimed to identify patterns of neural sensitivity to implicit peer influences, which involve more subtle cues that shape preferences and behaviors. Participants were 43 young adults (M_Age = 19.2 years; 24 males) who underwent functional magnetic resonance imaging while completing a task used to assess neural responses to implicitly "socially tagged" symbols (previously judged by peers as liked vs. not liked, thus differing in apparent popularity) vs. novel symbols that carried no social meaning (not judged by peers). Results indicated greater activity in brain regions involved in salience detection (e.g., anterior cingulate cortex) and reward processing (e.g., caudate) to socially tagged vs. novel symbols, and particularly to unpopular symbols. Greater self-reported susceptibility to peer influence was related to more activity in the insula and caudate when viewing socially tagged vs. novel symbols. These results suggest that the brain is sensitive to even subtle cues varying in level of peer endorsement and neural sensitivity differed by the tendency to conform to peers' behaviors particularly in regions implicated in social motivation.

Substance use escalates between adolescence and young adulthood, and most experimentation occurs among peers. To understand underlying mechanisms, research has focused on neural response during relevant psychological processes. Functional magnetic resonance imaging (fMRI) research provides a wealth of information about brain activity when processing monetary rewards; however, most studies have used tasks devoid of social stimuli. Given that adolescent neurodevelopment is sculpted by the push-and-pull of peers and emotions, identifying neural substrates is important for intervention. We systematically reviewed 28 fMRI studies examining substance use and neural responses to stimuli including social reward, emotional faces, social influence, and social stressors. We found substance use was positively associated with social-reward activity (e.g., in the ventral striatum), and negatively with social-stress activity (e.g., in the amygdala). For emotion, findings were mixed with more use linked to heightened response (e.g., in amygdala), but also with decreased response (e.g., in insula). For social influence, evidence supported both positive (e.g., cannabis and nucleus accumbens during conformity) and negative (e.g., polydrug and ventromedial PFC during peers' choices) relations between activity and use. Based on the literature, we offer recommendations for future research on the neural processing of social information to better identify risks for substance use.