Nicotine dependence and functional connectivity of insular cortex subregions

The insular cortex has been identified as a promising target in brain-based therapies for Tobacco Use Disorder, and has three major sub-regions (ventral anterior, dorsal anterior, and posterior) that serve distinct functional networks. How these subregions and associated networks contribute to nicotine dependence has not been well understood, and therefore was the subject of this study. Forty-seven individuals (24 women; 18-45 years old) who smoked cigarettes daily rated their dependence using the Fagerstrom Test for Nicotine Dependence (FTND), abstained from smoking overnight (~12 h), and underwent resting-state functional MRI. Correlations between dependence and resting-state functional connectivity (RSFC) of the major insular sub-regions were evaluated using whole-brain-corrected voxel-wise analyses and post-hoc region-of-interest (ROI) analyses. Dependence was analyzed both as a unitary (FTND total score) and bivariate construct - two FTND factors ("morning smoking" and "daytime smoking"). Dependence was negatively correlated with connectivity of both the right dorsal and left ventral anterior insula with the left precuneus, and with connectivity of the left posterior insula to the left putamen. In post-hoc analyses, dependence correlated negatively with connectivity between all anterior insula subregions and the left precuneus, and with bilateral posterior insula connectivity with the left posterior putamen. The latter finding was driven by "daytime smoking". These results suggest an anterior-posterior distinction in functional insular networks associated with different dimensions of nicotine dependence, with greater dependence linked to weaker connectivity. They may inform therapeutic approaches involving brain stimulation that may elicit differential clinical outcomes depending on the insular subnetwork targeted.