Unlike many previous studies, we used a whole-brain voxel-wise approach in order to localize gray matter change due to long-term exposure to cannabis. To this end, we used Voxel-based Morphometry (VBM), a completely automatic and unbiased data processing technique for the assessment of gray matter density. This technique has been already widely used in clinical research (Draganski and Bhatia, 2010) and in drug addiction (Connolly et al, 2013).
