”(Sutherland et al. 2012) In their model, the insula works in conjunction with the ACC. This model fits nicely with the sensitization–check FAQ homeostasis theory, which addresses how nicotine withdrawal generates a “homeostatically salient internal state.” Our data provide some support for the Sutherland model by demonstrating that the
withdrawal condition is associated with increased rsFC between the ACC and the insula that correlates with the intensity of WIC (Table Inhibitors,research,lifescience,medical (Table2C2C and D). Our structural analysis revealed a strong negative correlation between PD and white matter tracts connecting the frontal cortex and ACC. We speculate that this might be related to a loss of “top down” control of executive function over craving networks. (Heatherton and Wagner 2011) In a biofeedback
experiment, smokers were unable to “increase resistance” to tobacco craving by increasing activity in the medial prefrontal cortex. (Li et al. 2013) We selleck chemical Abiraterone observed Inhibitors,research,lifescience,medical stronger rsFC between the ACC and the frontal cortex during Inhibitors,research,lifescience,medical abstinence than during satiation, and in abstinent smokers as compared to nonsmoking controls. However, this activity did not correlate with WIC. ACC-frontal lobe circuits might relate to the brain’s attempts to suppress craving or to cope with disruptions to homeostasis caused by withdrawal, as suggested by Sutherland et al. (Sutherland et al. 2012). Strengths of our study design include a theory-driven analysis, the recruitment of smokers that represented the full spectrum of PD which allowed us to identify structural changes that track the progression of PD, the combination of structural and functional analyses, standardization of the length Inhibitors,research,lifescience,medical of abstinence for smokers, and the inclusion
of nonsmoking controls. A limitation of this study was the potential for order effects given that Inhibitors,research,lifescience,medical the abstinence condition always preceded the satiated condition. This could have been avoided by randomizing half the smokers to complete the satiated condition first, but this would have required 2 days of imaging for each subject, which was not possible given our budgetary limitations. We used a measure of WIC rather than a standardized instrument that addresses all withdrawal symptoms because of uncertainty about whether withdrawal symptoms Brefeldin_A such as headache, nausea, and increased appetite are central nervous system symptoms. Another limitation of this study is the small sample size. The small sample size made it relatively difficult to identify brain networks from the ICA results, thus further validation of our findings is necessary. However, the two approaches used in this study (ICA and seed-based analysis) presented highly consistent results, which suggest the robustness of our findings.