Among affected tracts within fronto-parietal networks, the left SLF showed prominently decreased FA and the greatest volume of anisotropic differences. As the SLF encompasses projections from parietal to dorsomedial and dorsolateral prefrontal cortices (Makris et al., 2005), this anatomic finding bears a potential association with the increased activation in right prefrontal and parietal areas evident during inhibitory processing (Tapert et al., 2007) and with the increased right parietal BOLD response observed during spatial working memory (Schweinsburg et al., 2008b) among marijuana users. Greater reliance on right frontal and cerebellar regions to adequately learn novel verbal material has also been documented in marijuana-using adolescents (Jacobsen et al., 2007) and speaks to the broad range of functional impact that may be associated with white matter deficits within the left SLF.
