Neural Correlates of Social Influence Among Cannabis Users

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.

Psychiatric comorbidity in adolescent use and poly-use of combustible, vaporized, and edible cannabis products

Cannabis legalization and commercialization has resulted in novel alternative cannabis products on the market, including edible and vaporized cannabis, which may appeal to youth with psychiatric problems. Psychiatric comorbidity in adolescent use and poly-use (i.e., use of >2 products) of combustible, edible, and vaporized cannabis products has largely gone uninvestigated. This 2015 cross-sectional survey of Los Angeles, California area adolescents (Mage = 16.1, N = 3177) characterized associations of various psychiatric problems with use and poly-use of combustible, edible, and vaporized cannabis. Exposure variables included past 30-day non-cannabis substance use (alcohol, e-cigarettes, combustible cigarettes, and nonmedical prescription opioid and stimulant use; yes/no), and psychiatric problems including past-week depressive symptom frequency, past 6-month ADHD symptom and conduct problem frequency, anhedonia, and five dimensions of impulsivity (sensation seeking, perseverance, lack of premeditation, positive urgency, and negative urgency). Outcome variables included past 30-day use (yes/no) of combustible, edible, and vaporized cannabis, independently, and number of cannabis products used (single, dual-use, poly-use). Results showed that all forms of non-cannabis substance use (ORs range: 13.7-36.1) and all psychiatric symptoms and traits (ORs in SD units range: 1.1-2.1) were positively associated with combustible, edible, and vaporized cannabis product use. The magnitude of comorbidity did not significantly differ by cannabis product type used in most cases. Psychiatric comorbidity was typically stronger in poly-product than single-product cannabis use and greater for externalizing-type than internalizing-type psychiatric problems. Practitioners, policy makers, and scientists should be aware that pervasive psychiatric comorbidity may be observed across the spectrum of cannabis product use among adolescents, particularly poly-product users.

Shifted balance of dorsal versus ventral striatal communication with frontal reward and regulatory regions in cannabis-dependent males

The transition from voluntary to addictive behavior is characterized by a loss of regulatory control in favor of reward driven behavior. Animal models indicate that this process is neurally underpinned by a shift in ventral-dorsal striatal control of behavior; however, this shift has not been directly examined in humans. The present resting state functional magnetic resonance imaging (fMRI) study employed a two-step approach to: (a) precisely map striatal alterations using a novel, data-driven network classification strategy combining intrinsic connectivity contrast with multivoxel pattern analysis and, (b) to determine whether a ventral to dorsal striatal shift in connectivity with reward and regulatory control regions can be observed in abstinent (28 days) male cannabis-dependent individuals (n = 24) relative to matched controls (n = 28). Network classification revealed that the groups can be reliably discriminated by global connectivity profiles of two striatal regions that mapped onto the ventral (nucleus accumbens) and dorsal striatum (caudate). Subsequent functional connectivity analysis demonstrated a relative shift between ventral and dorsal striatal communication with fronto-limbic regions that have been consistently involved in reward processing (rostral anterior cingulate cortex [ACC]) and executive/regulatory functions (dorsomedial prefrontal cortex [PFC]). Specifically, in the cannabis-dependent subjects, connectivity between the ventral striatum with the rostral ACC increased, whereas both striatal regions were uncoupled from the regulatory dorsomedial PFC. Together, these findings suggest a shift in the balance between dorsal and ventral striatal control in cannabis dependence. Similar changes have been observed in animal models and may promote the loss of control central to addictive behavior.