Specific Associations in the Alpha Frequency Between the Subcomponents of Rumination and the Subsystems of the Default Mode Network Among Bipolar I Disorder Patients

<b><i>Introduction:</i></b> Rumination in bipolar disorder (BD) is well documented. Recent neuroimaging studies highlight the role of the default mode network (DMN) in rumination, while few studies have evaluated the DMN activity in BD rumination, particularly the underlying neuroelectrophysiology. <b><i>Methods:</i></b> A total of 44 patients with depressed bipolar I disorder (BD-I) and 46 healthy controls underwent resting-state magnetoencephalography. Two core hubs of the DMN, the posterior cingulate cortex (PCC), and anterior medial prefrontal cortex, together with the dorsal medial prefrontal cortex (dmPFC) and the medial temporal lobe (MTL) subsystems, were identified as the regions of interest. The power envelope method was used to determine the alpha band's cross-subsystem functional connectivity (FC). After comparing the rumination and DMN FC between the groups, Spearman partial correlation analysis was performed to evaluate the relationship between aberrant FC and rumination in BD-I patients. <b><i>Results:</i></b> BD-I patients demonstrated more global rumination, including higher subcomponent scores of brooding and reflection. In addition, the alpha frequency FC of the PCC-dmPFC and dmPFC-MTL subsystems within the DMN was dramatically increased in the BD-I group. The former was strongly associated with reflection, whereas the latter was related to brooding. <b><i>Conclusion:</i></b> The findings suggest that the reflection and brooding components of rumination are selectively related to the alpha frequency FC of the PCC-dmPFC and dmPFC-MTL subsystems, respectively. These associations highlight the significance of DMN activities in rumination among BD-I patients and have implications for future rumination interventions.