Hierarchical regression analyses of FA in the right occipital region (MJ+ALC FA > Control FA) indicated a significant FA × group interaction in predicting performance on D-KEFS TMT Switching (β = 3.85; p <.001). Simple effects analyses revealed that higher FA was associated with better performance on TMT Switching in the MJ+ALC group (β = .55; p <.01) (see Figure 1). Concomitant with this finding, an interesting trend emerged suggesting that higher FA in this region was associated with poorer performance on TMT Switching in controls (β = -.32; p=.06). When predicting CVLT-II List A Trial 1 scores, a significant FA × group interaction (β = 2.16; p<.05) indicated that for users only, increased FA in the right occipital region was associated with better Trial 1 performance (β = .47; p <.01). Controls did not show a significant relationship between FA in this region and Trial 1 performance. FA in the right anterior limb of the internal capsule, another cluster in which FA in MJ+ALC users exceeded that of controls, predicted performance on WMS-III Logical Memory II delayed recall for both groups (β = -.31; p<.05). The group main effect and FA × group interaction were nonsignificant.
