Default mode network subsystem alterations in bipolar disorder during major depressive episode

Background: Default mode network (DMN) has been widely reported to be altered in bipolar disorder during major depressive episode (BDD). Recent studies supported the idea that DMN is not an unitary system, but composed of smaller and distinct functional subsystems. The current study aimed to investigate the abnormal functional connectivity (FC) patterns of DMN subsystems in BDD. Methods: Seed-based FC method was applied to extract 11 DMN components in resting-state functional magnetic resonance imaging data acquired from 40 patients with BDD and 63 demographically matched healthy controls. Results: Patients showed reduced FC between precuneus and all three DMN subsystems. Additionally, in the midline core, patients revealed increased FC between posterior cingutate cortex (PCC) seed and lateral orbitofrontal cortex. In the dorsomedial prefrontal cortex and medial temporal lobe subsystems, patients demonstrated increased FC with sensorimotor, visual, and salience network regions. Furthermore, the abnormal FC between the PCC seed and precuneus was correlated with high pessimism. Limitations: Our sample size is relatively small, limiting the power to detect subtle group differences and significant correlations between brain connectivity and clinical variables. In addition, most of our patients have been treated with medications. Conclusion: Our findings revealed the abnormal FC patterns of DMN subdivision circuits and highlighted these abnormalities were associated the pathological mechanisms in BDD.