The brain in social context: A systematic review of substance use and social processing from adolescence to young adulthood.

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.

Neural Response to Social Exclusion Moderates the Link Between Adolescent Anxiety Symptoms and Substance Use.

BACKGROUND: Substance use (SU) typically increases from middle to late adolescence. Anxiety is one factor associated with greater SU, although variability in who uses substances remains. Some models suggest that brain-based susceptibility markers could reveal which adolescents are at a higher risk for psychopathology, but it is unknown whether these individual differences attenuate or accentuate the association between anxiety and elevated SU even if normative. This study addressed this gap by testing whether neural response to social exclusion moderates the association between anxiety symptoms and increased SU from middle to late adolescence. METHODS: Participants were 181 Mexican-origin adolescents (48% female; 16-17 years old) who completed a social exclusion task during a functional magnetic resonance imaging scan and filled out questionnaires about their SU and anxiety symptoms. Analyses focused on neural response to social exclusion versus inclusion within 3 regions of interest and change in SU across 2 years. RESULTS: Dorsal anterior cingulate cortex response to social exclusion, but not subgenual anterior cingulate cortex or anterior insula, moderated the relation between anxiety symptoms and SU, such that higher anxiety symptoms predicted a greater relative increase in SU only for those youth with a lower dorsal anterior cingulate cortex response to exclusion. CONCLUSIONS: Blunted dorsal anterior cingulate cortex response to social exclusion may serve as a neural susceptibility marker of altered conflict monitoring or emotion regulation in middle adolescence that, in combination with high levels of anxious feelings, elevates the risk for onset of and/or increased SU by late adolescence. These findings have implications for designing targeted interventions to mitigate SU among adolescents.

Neural responses to implicit forms of peer influence in young adults.

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 (MAge = 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.

Reward-Related Brain Activity Prospectively Predicts Increases in Alcohol Use in Adolescents.

OBJECTIVE: Altered activity within reward-related neural regions, including the ventral striatum (VS) and medial prefrontal cortex (mPFC), is associated with concurrent problematic substance use. The aims of the present study were (a) to identify patterns of reward-related neural activity that prospectively predicted changes in alcohol use 2 years after magnetic resonance imaging in a sample of adolescents, and (b) to examine whether these patterns differed by sex. We also tested whether depression symptoms or impulsivity mediated associations between neural activity and future alcohol use. METHOD: Participants were 262 adolescents (129 male and 133 female) of Mexican origin who completed the Monetary Incentive Delay task during a functional magnetic resonance imaging scan at age 16. Participants reported on their alcohol use at ages 16 and 18. RESULTS: Results indicated that different patterns of reward-related neural activity predicted future increases in alcohol use for male and female adolescents. In boys, higher VS activity during reward anticipation and average ventral mPFC activity during reward feedback predicted increases in alcohol use from age 16 to 18 years; in girls, higher dorsal mPFC activity and blunted VS activity during reward anticipation predicted increases in alcohol use from age 16 to 18 years. Depression symptoms or impulsivity did not mediate these associations. CONCLUSION: The results suggest that different pathways of risk may lead to problematic alcohol use for adolescent boys and girls. These sex differences in neural risk pathways have important implications for prevention and intervention approaches targeting Mexican-origin youth.