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A Functional Connectivity Study of Verbal and Perceptual Reasoning in Bipolar Disorder
One recent meta-analysis demonstrated that all cognitive domains had medium to large effect sizes for impairment in euthymic bipolar disorder compared to controls, save verbal intelligence, suggesting that verbal ability or ‘crystalized intelligence’ remains more intact. Therefore, we investigated the underlying pathophysiology of perceptual reasoning or ‘fluid intelligence’ and ‘crystalized intelligence’ to determine abnormalities underlying these cognitive processes.
Twenty-five bipolar patients and 21 controls completed a lexical decision task (LDT) and Raven’s Progressive Matrices (RSPM) task during fMRI. The LDT consisted of discriminating real words versus pseudo-words and had easier and harder conditions. The RSPM consisted of completing a matrix and had easier, medium, and harder conditions. To comprehensively evaluate brain networks involved in the tasks, constrained principal component analysis for fMRI (fMRI-CPCA) was used.
Three networks were found for the LDT, default mode (DMN), language, and response/visual attention/DMN. Bipolar patients maintained higher activation following the hemodynamic response (HDR) peak in the response/visual attention/DMN in the pseudo-word and hard conditions compared to controls. Four networks were found for the RSPM task, DMN, visual attention, response/DMN, and visual attention capture. Controls had later reactivation of the DMN compared to bipolar patients. For the response/DMN, bipolar patients showed stronger pre-HDR peak activation and post-HDR peak deactivation compared to controls.
Bipolar patients demonstrate abnormalities in coordinated brain activity across both perceptual and verbal reasoning compared to controls, with different networks impacted; however, activation in the language network was preserved for the LDT.