There were widespread negative associations between cigarette pack-years and decreased neocortical volume adjusted for total intracranial volume (Figure 2). Of the 11 correlations that were significant, genetic covariances substantially contributed to associations in five specific cortical ROIs, which are located in the frontal, occipital, parietal, and cingulate lobes. The significant genetic influences shared between smoking and these ROIs (-0.17 < covA < -0.12; p = 0.01-0.05) contributed to the majority of the phenotypic correlations between cigarette pack-years and their respective volumetric measures (-0.18 < rP < -0.11, p = 0.01-0.10) in the right pars opercularis, right lingual gyrus, right caudal anterior cingulate, and right precuneus. The magnitude of the genetic correlations indicate moderate overlap between the shared genetic factors which increase cigarette pack-years and decrease volume in these ROIs (-0.40 < rA < -0.31; Table I).
