Collections > Electronic Theses and Dissertations > Structural abnormalities within the episodic prospection and decision making circuitry in cigarette smokers: a DTI and sMRI analysis
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Smokers characteristically show a heightened tendency to select smaller, sooner over larger, delayed rewards, and the neurobiology of such decision making is beginning to come to light. For instance, recent studies in healthy people show that engaging episodic prospection during such decision making can reduce impulsive choices, and that this effect is mediated by enhanced functional connectivity between medial temporal lobe regions implicated in episodic prospection and frontal areas. Through this study we sought to determine if there are any structural differences between cigarette smokers and non-smokers in the episodic prospection and decision making circuitry through the use of diffusion tensor imaging (DTI) and structural MRI (sMRI) analysis. Further, we investigated whether there were any structural changes in this circuitry within smokers that correlated with measurements of cigarette consumption (cigarettes per day, breath carbon monoxide), and addiction severity (cigarette dependence scale). Specifically we studied the white matter (WM) tracts the cingulum, fornix, and uncinate, and the grey matter (GM) regions that these tracts connect, namely regions of the medial temporal lobe and the prefrontal cortex. Our hypotheses were that smokers would have decreased WM structural integrity in the tracts bilaterally compared to nonsmokers, and that the brain regions served by these tracts would have decreased volume and thickness in smokers compared to non-smokers. Within smokers, we hypothesized that with increasing cigarette consumption and addiction severity there would be decreased WM integrity, and decreased regional GM volume and thickness. We acquired diffusion weighted and anatomical MR images from nonsmokers (<italic>n</italic>=15) and smokers (<italic>n</italic>=10 (11 for sMRI)), aged 19-40 years old. We developed and utilized a novel framework for DTI analysis, the UNC-Utah NA-MIC Framework for DTI Fiber Tract Analysis. We found smokers to have decreased WM integrity in the fornix crus, and decreased hippocampal volume compared to nonsmokers. Looking just within smokers, we found positive correlations between WM integrity and measurements of cigarette consumption and addiction severity for the fornix and cingulum. GM analysis though showed negative correlations between these same smoking indices and measurements of cortical thickness and volume in the inferior frontal gyrus, lateral orbitofrontal cortex, cingulate, and amygdala. Together these results demonstrate that the circuitry for episodic prospection, decision making, and cognitive control are altered in cigarette smokers and that the structural aberration correlates with measures of cigarette consumption and dependence.