Peter Grund

Adolescence is a sensitive period of neurodevelopment partially characterized by enhanced susceptibility to impulsive decision-making. Impulsivity predisposes individuals to risk-taking behaviors, including substance abuse—greater temporal discounting is reliably associated with substance abuse. Participants (N=74) completed a five-wave longitudinal study of adolescent brain and behavioral development, completing a delayed discounting task at each assessment point. The task calculated participants' indifference points at 6 distinct temporal intervals. Participants were sorted into groups based on frequency and type of substance use post-initiation: alcohol use only (AO; N=32), infrequent marijuana use (IAM; N=25), or frequent marijuana use (FAM; N=17). The impact of age on delay discounting was examined. Mean delay discounting area-under-the-curve (AUC) scores were compared between groups at assessment points pre- and post-initiation of substance use controlling for relevant covariates. Age prior to substance use initiation was correlated with both pre-AUC (r(75)=0.345; p=0.002) and post-AUC (r(80)=0.271; p=0.015). At the time point preceding substance involvement, a one-way ANCOVA with continuous covariates of age and verbal IQ yielded a significant effect of group on mean AUC scores prior to the initiation of substance use (F=4.835, p=0.002). Follow-up post-hoc tests revealed FAM had reduced AUC scores relative to AO users (p=0.018), but not IAM (p=0.082). Analyzing individual indifference points (IPs) suggested that FAM’s reduced AUC scores were largely driven by steep discounting slopes between the 10, 30, and 180 day IPs.