Given the frequency of comorbid marijuana and alcohol use and their potential interaction, the extent of underlying circuitry disruptions and neurocognitive consequences needs further elucidation. Using diffusion tensor imaging (DTI), we previously characterized the relationship between marijuana and alcohol use and WM integrity among adolescent users and age-matched controls (Bava et al., 2009). Decreased fractional anisotropy (FA) was found most prominently in frontal-parietal circuitry comprising fibers of the inferior frontal region, splenium of the corpus callosum, postcentral gyrus, and left superior longitudinal fasciculus (SLF). Although mean diffusivity (MD) was similar between groups in regions of FA discrepancy, MD in WM adjacent the lingual gyrus was higher in users but lower in the inferior longitudinal fasciculus (ILF) as compared to controls. These findings suggest the presence of selective aberrancies in cerebral WM in adolescent marijuana and alcohol use, and are the basis for neurobehavioral correlation in the current study.
