Brain networks in bipolar disorder II: a resting-state fMRI study

Bipolar disorder II (BD-II) is characterized by hypomanic and depressive episodes, accompanied by mild cognitive deficits, which can be postulated to be due to emotional and cognitive dyscontrol, with attention as the binding factor. Structural and functional magnetic resonance imaging (fMRI) have implicated several brain regions across the BD spectrum, including the prefrontal cortex (PFC), cingulate cortex and amygdala. Newer studies also look at whole brain networks using resting-state fMRI (RS-fMRI). A notable RS network is the default-mode network (DMN), typically activated at rest and associated with mind wandering. The aim of the current study was to characterize functional brain networks specifically in BD-II patients (n = 32) by assessing of within and between network connectivity against healthy controls (n = 35) through RS-fMRI (age 18-50). We also assessed the subjects on working memory measures using the RAVLT and BVMT-R. Independent component analysis and dual regression was used for within-network analysis, and FSLNets was used for between-network connectivity and network modeling. Based on earlier findings, we predicted aberrant connectivity within the DMN, increased connectivity within the anterior cingulate cortex, decreased connectivity between the ventrolateral PFC and amygdala, and decreased connectivity between the posterior cingulate cortex and DMN. We also expected visual networks to display increased connectivity to the amygdala. Decreased test performance was observed on the BVMT-R, and decreased delayed recall on the RAVLT. We found no statistically significant changes in connectivity within or between networks, indicating that brain networks in BD-II are not significantly different from healthy individuals.