In the absence of correlations between pack-years with neocortical surface area or thickness, it is possible that there could be correlations with volume. For example, this might suggest an interactive effect. Here, the neocortical regions with significant correlations between pack-years and volume tended to have significant surface area correlations (although not always on the same side). Further, given the relative consistency in results measured either as volume or surface area, it is important to note that any relationships identified between cortical volume measures and smoking are likely to be due to cortical surface area. These results are similar to prior studies where differences in cortical gray matter volume were driven almost exclusively by differences in surface area (Im et al. 2008; Pakkenberg and Gundersen 1997). Cortical surface area has been reported as an appropriate descriptor to study brain network organization (Sanabria-Diaz et al. 2010) and the significant relationships between surface area and pack-years may reflect networks related to smoking-related behaviors. Prior data from animal, human and in vivo studies have identified four distinct neurological networks for smoking (O'Doherty et al.
