Voxel-by-voxel correlations over the whole brain were performed merging the two groups together. Correlation analysis highlights an inverse linear correlation between GM volume and the monthly frequency of cannabis use during the 3 months before inclusion in the study. Regions with a decreased GM volume in regular smokers (Table 2) are those that exhibit this inverse correlation (P<0.005). Figure 2 (panel a) illustrates this relation in three clusters located in the left parahippocampal gyrus (P=0.004, R=−0.42), left insula (P=0.0002, R=−0.54), and right temporal pole (P=0.002, R=−0.45). The results for the other four regions are presented in the Supplementary File S1.
