Regression analyses, which allowed us to examine the relationship between marijuana use and BOLD signal changes, also yielded interesting findings. Within the chronic, heavy marijuana smokers, the total number of smoking episodes per week was positively associated with cingulate activity during the viewing of masked angry faces. This region was nearly identical to the area of greatest activation seen when marijuana smokers were contrasted with non-marijuana smoking control subjects during the viewing of masked angry faces, highlighting the importance of the association between marijuana use and activation change. Within the marijuana smokers, total number of smoking episodes per week was also positively associated with amygdalar activity during the viewing of masked happy faces, with coordinates virtually overlapping those seen for the non-marijuana smoking controls during the viewing of masked happy faces. Finally, overall urinary cannabinoid level was positively related to cingulate activity during the viewing of masked happy faces, in approximately the same region as demonstrated for the chronic, heavy marijuana smokers compared to the non-marijuana smoking controls during the viewing of masked happy faces. The positive associations between marijuana
