Orbitofrontal cortex volume links polygenic risk for smoking with tobacco use in healthy adolescents

Association between vmPFC gray matter volume and smoking initiation in adolescents

Smoking of cigarettes among young adolescents is a pressing public health issue. However, the neural mechanisms underlying smoking initiation and sustenance during adolescence, especially the potential causal interactions between altered brain development and smoking behaviour, remain elusive. Here, using large longitudinal adolescence imaging genetic cohorts, we identify associations between left ventromedial prefrontal cortex (vmPFC) gray matter volume (GMV) and subsequent self-reported smoking initiation, and between right vmPFC GMV and the maintenance of smoking behaviour. Rule-breaking behaviour mediates the association between smaller left vmPFC GMV and smoking behaviour based on longitudinal cross-lagged analysis and Mendelian randomisation. In contrast, smoking behaviour associated longitudinal covariation of right vmPFC GMV and sensation seeking (especially hedonic experience) highlights a potential reward-based mechanism for sustaining addictive behaviour. Taken together, our findings reveal vmPFC GMV as a possible biomarker for the early stages of nicotine addiction, with implications for its prevention and treatment.

Orbitofrontal cortex thickness and substance use disorders in emerging adulthood: causal inferences from a co-twin control/discordant twin study

BACKGROUND/AIMS

Research linking orbitofrontal cortex (OFC) structure and substance use disorders (SUDs) is largely correlational and often implies a causal effect of addiction/substance exposure on the brain, but familial risk factors (e.g. genetic liability) may confound these associations. We tested whether associations between alcohol, cannabis and tobacco use disorders and OFC thickness reflected the potential causal effects of familial risk or SUDs-related consequences (e.g. substance exposure).

DESIGN

A co-twin control/discordant twin design separated familial risk confounding from SUD-related consequences.

SETTING/PARTICIPANTS

A population-based sample of 436 24-year-old twins (62% monozygotic) from the Minnesota Twin Family Study, USA.

MEASUREMENTS

Alcohol, cannabis and tobacco use disorders were assessed using the Composite International Diagnostic Interview-Substance Abuse Module. Cortical thickness of the medial and lateral OFC (mOFC and lOFC, respectively) was assessed using magnetic resonance imaging (MRI).

FINDINGS

Lower mOFC (P-values ≤ 0.006) but not lOFC (P-values ≥ 0.190) thickness was observed in diagnosed individuals (n = 185) relative to non-SUD controls (n = 251). Co-twin control analyses offered evidence that mOFC associations were consistent with familial risk across SUDs (between-pair effect: P-values ≤ 0.047) and the independent consequences of having an alcohol or cannabis use disorder (within-pair effect: P-values ≤ 0.024). That is, within alcohol/cannabis discordant twin pairs, affected twins had significantly lower mOFC thickness compared with their unaffected co-twins.

CONCLUSIONS

A confounder-adjusted analysis of the Minnesota Twin Family Study appeared to indicate that, beyond a substance use disorders general familial risk effect, the experience of an alcohol or cannabis use disorder in emerging adulthood reduces the thickness of the medial orbitofrontal cortex, a region associated with value-guided decision-making.