Recent DTI work in young adults with history of cannabis dependence shows reduced FA, increased radial diffusivity, and increased MD in the bilateral posterior internal capsule/thalamic radiation, left middle temporal gyrus and right superior temporal gyrus (Ashtari et al., 2009). Vulnerability in fronto-temporal areas bears resemblance to the current findings, though predominance of parietal changes in our group may reflect more heterogeneous use of both cannabis and alcohol in our group. Another study of adults who used moderately as adolescents suggests no changes in white matter structure relative to non-users (Delisi et al., 2006). Although this study may indicate a reversibility of white matter changes with long-term abstinence, current alcohol use in 20% of their sample suggests the possibility that methodological factors may contribute to inconsistencies with the current findings. Our diffusion protocol, employing comparatively higher angular resolution and increased image resolution may yield increased sensitivity to white matter alterations. Similarly, differences in power and sample characteristics (e.g, chronicity of substance use) could impact detection of significant effects. Also diverging from the present study is a recent report of higher
