water molecules along fiber tracts, and mean diffusivity (MD), reflecting the degree of overall displacement of water molecules in localized tissue [51,75]. Based on literature examining combined effects of alcohol and cannabinoids on neural toxicity in the immature brain [40] and data from our lab showing abnormal brain functioning in abstinent adolescent marijuana users [81,94] and binge drinkers [56], we hypothesized that histories of binge drinking alone and in combination with marijuana would be linked to poorer white matter fiber tract coherence and organization (i.e., lower FA) compared to controls. We further hypothesized that in regions where FA was low in users, MD values would be higher, reflecting tissue loss or potential demyelination.
