White matter fibers within the bilateral crus cerebri also showed diminished FA. As important structural constituents of the fronto-cortico-striatal and corticopontocerebellar circuits, prior studies show a uniform decrease in these regions in disorders of attention (Ashtari et al., 2005) and first episode schizophrenia (Cheung et al., 2008). Although the internal capsule has shown corresponding diminutions in these populations, MJ+ALC users showed a departure from this trend, evidencing increased FA in the anterior limb. This aspect of the internal capsule contains both direct and indirect fronto-thalamic projections. Collectively, changes in the crus cerebri, internal capsule, and inferior frontal tracts may be consistent with aberrant corticothalamic and frontostriatal connectivity, and fit with previous reports of volumetric increases in the right thalamus and greater striatal activation during working memory tasks (Kanayama et al., 2004; Matochik et al., 2005; Padula et al., 2007).
