The significant unique environmental factors shared between cigarette pack-years and subcortical regions contributed to the significant phenotypic correlations in the left nucleus accumbens and left pallidum. Previous structural MRI studies have identified significant negative phenotypic correlations between ventral striatum/nucleus accumbens in case-control studies (Brody et al. 2004) and in community-based samples (Das et al. 2012). Further, these ROIs have been previously identified to be important in pathways involved in the processing of the effects of nicotine administration in the presence of nicotine-related environmental stimuli (Smith et al. 2011; David et al. 2005). These results emphasize the importance of the role of environmental cues such as daily stressors or exposure to social situations within specific networks of smoking-related behaviors.
