<qa>  What is the primary hypothese for the proposed research?Based on prior literature and pilot data collected during the previous Merit Review period, the primary hypotheses for the proposed research are that: 1 Participants who are heavy MJ users will have higher 4 2 nAChR densities in the thalami and other brain regions than participants who are not heavy MJ users, 2 Participants who are daily heavy caffeine users will have lower 4 2 nAChR densities in the thalami and other regions than participants who are not heavy daily caffeine users, 3 Densities of 4 2 nAChRs in the thalami and other brain regions of interest will be higher in menthol than non-menthol cigarette smokers, and 4 lesser severity of 4 2 nAChR up-regulation at baseline along with clinical factors such as lesser severity of nicotine dependence will be associated with better treatment outcomes in a standard smoking cessation program, including an improved likelihood of quitting andor decreasing smoking. 