Results from the bivariate analyses between cigarette pack-years and brain morphometry provide a deeper characterization into the etiology of smoking-related behaviors. Cortical and subcortical structures were identified that have previously been reported to play a role in specific aspects of networks of smoking-related behaviors, particularly craving control and reward/pleasure. This exploratory study demonstrated widespread, shared genetic and environmental influences on phenotypic correlations between brain structure and cigarette pack-years. These results are expected to guide future genetic association studies in neuroimaging and smoking as well as future models testing the role of specific environmental risk factors in brain circuits related to smoking-related behaviors. Future tests of these relationships in the presence of additional covariates will also help to guide understanding of etiology of nicotine dependence since no adjustments were made for the effects of covariates such as comorbid drug or alcohol use or cardiovascular disease nor were there any exclusions for participants with psychiatric history, psychotropic medication use, active combat exposure, head trauma, or hearing/speech impairment. Further, these results do not imply any direction of causation between cigarette pack-years and brain
