Author: Humberto Monsivais, Brian A. Taylor, Francesco Versace 👨🔬
Affiliation: Purdue University, Department of Behavioral Science, Division of Cancer Prevention and Population Sciences, The University of Texas MD Anderson Cancer Center, Department of Imaging Physics, The University of Texas MD Anderson Cancer Center 🌍
Purpose: To identify possible signatures of altered brain morphometry in nicotine-dependency via a structural covariance network approach.
Methods: Fifty-one healthy controls (HC:27M, mean age=39±14 SD, 24F, mean age=43±13) and fifty-one smokers (SM:26M, mean age=45±14, 25F, mean age=50±9) underwent brain scans on a whole-body 3T MRI system (Siemens Healthineers). T1-weighted structural images were acquired with a 3D MPRAGE sequence. Surface-based morphometry was used to estimate the cortical gray matter thicknesses (cGMTs) of brain regions using the Computational Anatomy Toolbox (CAT12, v12.9) in SPM12 following the recommended defaults. Intra-individual structural covariance networks were constructed at the individual level, using bilaterally-averaged data from 31 cGMTs. The edge weights in these networks reflected the degree of similarity between cortical thickness changes in the brain, quantified by their z-score transformations relative to healthy controls. Global network properties were examined through metrics of network segregation (clustering coefficients and modularity), network integration (global efficiency), and their equilibrium (small-worldness). Regional network hubs were analyzed using (rank-transformed) betweenness, closeness, and eigenvector centrality measures.
Results: While global metrics did not significantly differ between the HC and SM groups, the HC network shows signs of more balanced connectivity, whereas the SM network suggests a shift toward hub-dominated connectivity. At the regional level, there were lower eigenvector centrality values (a measure of the "most influential" brain regions in the network) in the SM group for the caudal anterior cingulate cortex (p-adj:0.02), post-central gyrus (postC, p-adj:0.01), superior-temporal gyrus (p-adj:0.02), and the entorhinal cortex (p-adj:0.03).
Conclusion: In summary, the findings of this study, point to a more segregated organization of structural covariance networks in smokers, and reorganization of brain hubs in the frontal lobe. These hubs may play a critical role in smoker’s brain organization, potentially reflecting adaptations/disruptions in regions associated with reward and cognitive control.