this, pre-onset use white matter integrity in MJ+ALC users is unknown, and pre-existing vulnerabilities including increased incidence of behavioral dysregulation (Kirisci et al., 2004; Tarter et al., 2003) and negative affectivity (Chassin et al., 2004) may be associated with neurological differences that predispose individuals in this group to substance use. Further, MJ+ALC users were more likely to have a parental history of substance use disorders. Considering that white matter changes in adolescent MJ+ALC users may have predated the onset of use, future follow-ups of this cohort will help determine whether increases in substance use result in greater deviations in white matter microstructure. Assessments prior to MJ+ALC use onset will provide important information on the relative influence of premorbid characteristics and initiation of heavy substance use.
