One unexpected finding indicated that FA in the anterior limb of the internal capsule, a region of higher FA in users, was associated with poorer performance on a measure of contextual verbal memory. This relationship departs from the compensatory model and suggests that elevated anisotropic diffusion may have adverse impact on brain function and neurocognitive performance. Higher FA in adolescent substance users, with primary MJ+ALC dependence, has been reported previously and related to premature myelination (De Bellis et al., 2008). The mechanism proposed is one wherein accelerated development could interfere with the formation or efficiency of typical functional networks. As such, increased FA in the anterior limb of the internal capsule may hinder connections with prefrontal, cingulate and thalamic fibers (Parent, 1990) and prove disadvantageous for cognitive performance.
