Common brain cortical abnormality in smoking behavior and bipolar disorder: discriminant analysis using cortical thickness and surface area.

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Cigarette smoking is highly prevalent among patients with bipolar disorder (BD). Structural brain abnormalities related to smoking behavior and BD risk are indicated by magnetic resonance imaging (MRI) studies. However, cortical alterations common to smoking behavior and BD remain unclear. Our purpose was to identify common cortical alterations between smoking behavior and BD. 3T MRI-based indices of cortical thickness and surface area using FreeSurfer were acquired from 166 healthy control (HC) nonsmokers, 39 HC smokers, 33 BD nonsmokers, and 18 BD smokers. A stepwise discriminant-function analysis (DFA) with cortical structures as predictors was performed to classify BD patients into nonsmokers and smokers. Next, DFAs with the selected structures as predictors were performed to discriminate smoking status or diagnostic status. Differences in the selected features among the four groups were examined. The first DFA showed that six brain features discriminated between nonsmokers and smokers among BD patients. The six brain features related to BD smoking status also discriminated between HCs and BD patients and HC nonsmokers and BD smokers. Among the six features, left insular thickness showed a negative additive effect of smoking status and BD diagnosis. Our findings suggest the common neurobiological involvement of insular thickness in smoking behavior and BDrisk.