Four studies have used DTI to examine the integrity of white matter tracts in chronic cannabis users [144], [147], [150], [151], of which half have reported positive results [144], [147]. Arnone et al. (2008) [144] found increased mean diffusivity (MD) in the corpus callosum while Gruber et al. (2011) [147] found increased MD in the right genu as well as reductions in left frontal fractional anisotropy (FA). Gruber et al. (2011) [147] also reported a positive association between left frontal FA and impulsivity scores, and higher FA and lower MD in the frontal lobes being associated with a later age of initiation of cannabis use.
