As reported in our previous study, independent samples t-tests, corrected for multiple comparisons with intensity and cluster-based thresholding, revealed 10 clusters (≥ 54 μl) in which MJ+ALC teens showed significantly lower FA than controls (Bava et al., 2009). The most prominent areas of decreased FA for users were found in the left SLF, left postcentral sensory gyrus, and bilateral crus cerebri (p<.001). Temporal regions including the right superior temporal gyrus (p<.001), projection fibers of the left temporo-thalamic tract (p<.01), and right ILF (p<.01) also showed lower FA in MJ+ALC users, as did association fibers in right inferior frontal (p<.001), left occipital-frontal (p<.01), and splenium (p<.01) regions (p-values refer to group difference in FA averaged across each cluster). Interestingly, in three right hemisphere clusters, MJ+ALC users had higher FA than controls (p<.001): the cuneus region of the occipital lobe, anterior limb of the internal capsule, and arcuate portion of the right SLF.
