In contrast to the animal literature, the investigation of the structural effects of long-term cannabis use on the human brain has brought less consistent findings. Changes in gray or white matter density have been reported in different locations in frontal and parietal lobes without overlapping findings across studies (Churchwell et al, 2010; Gruber et al, 2011; Matochik et al, 2005). The discrepancy in the results might be due to heterogeneity in sample characteristics, inter-individual differences linked to past history of drug use, amount of consumption, related psychological problems (temperament, level of anxiety or arousal), and/or methodological differences in data processing (Batalla et al, 2013; Lorenzetti et al, 2010). However, changes in the hippocampus/parahippocampal complex and in the amygdala have often been reported (Demirakca et al, 2011; Matochik et al, 2005; Yücel et al, 2008; Zalesky et al, 2012). These findings suggest that long-term cannabis use is associated with brain morphology alterations in regions linked to memory and executive and affective processing (Yücel et al, 2008).
