Abstract
BACKGROUND: Given the insula's role in the representation of bodily states associated with hedonic (i.e., enhancement motives) and aversive (i.e., craving) aspects of substance use, this longitudinal study examined associations between insula structure (i.e., white matter [WM] and gray matter [GM] volume), enhancement motives for alcohol and cannabis use, craving for alcohol and marijuana, and alcohol and cannabis involvement in treated adolescents. Enhancement motives and craving, as conscious representations of bodily states associated with use, were hypothesized as mediators (i.e., linking mechanisms) of the association between insula volume and substance use. METHODS: Adolescents (age 14 to 18, N = 30) recruited from substance use treatment reported on enhancement motives and obsession/craving for both alcohol and cannabis at baseline (near the start of treatment), and on alcohol and cannabis involvement (e.g., binge drinking, alcohol abuse/dependence symptom count) at baseline and over 1-year follow-up. Insula WM and GM volumes were determined using FreeSurfer. RESULTS: Enhancement motives for drinking served as a link between left insula WM volume and frequency of binge drinking at baseline and 1-year follow-up. This novel finding is consistent with the insula's role in representing bodily states (e.g., "high" associated with binge drinking) that can motivate drinking behavior. Although right insula WM volume was positively correlated with obsession/craving for alcohol, and obsession/craving was positively correlated with alcohol outcomes, the indirect effect was not significant. Insula WM volume was not associated with cannabis-related variables. Insula GM volume was not associated with enhancement motives, obsession/craving, or alcohol involvement. CONCLUSIONS: Enhancement motives for alcohol use, but not obsession/craving for alcohol, provided an important link between left insula WM volume and frequency of binge drinking in treated adolescents. Results are consistent with the insula's role in the processing of hedonic bodily states available to conscious awareness, particularly in the form of enhancement motives for alcohol use.