The subsystem mechanism of default mode network underlying rumination: A reproducible neuroimaging study

Rumination, a repetitive self-focused thinking style common in depression, is linked to abnormalities in the default mode network (DMN) of the brain. This study used a novel continuous-state paradigm to directly induce rumination or distraction in healthy participants across three MRI scanners. Results showed that during rumination, connectivity within the DMN generally decreased compared to distraction. Specifically, connectivity increased between the core and medial temporal lobe subsystems and decreased between the core and dorsal medial prefrontal cortex subsystem, as well as within the medial temporal lobe subsystem. Behavioral measures of rumination negatively correlated with connectivity between the core and dorsal medial prefrontal cortex subsystems, suggesting that rumination involves altered interactions among DMN components.

Study at a glance

Abstract

Rumination is a repetitive self-referential thinking style that is often interpreted as an expression of abnormalities of the default mode network (DMN) observed during "resting-state" in major depressive disorder (MDD). Recent evidence has demonstrated that the DMN is not unitary but can be further divided into 3 functionally heterogenous subsystems, although the subsystem mechanistically underlying rumination remains unclear. Due to the unconstrained and indirect correlational nature of previous resting-state fMRI studies on rumination's network underpinnings, a paradigm allowing direct investigation of network interactions during active rumination is needed. Here, with a modified continuous state-like paradigm, we induced healthy participants to ruminate or imagine objective scenarios (distraction, as a control condition) on 3 different MRI scanners. We compared functional connectivities (FC) of the DMN and its 3 subsystems between rumination and distraction states. Results yielded a highly reproducible and dissociated pattern. During rumination, within-DMN FC was generally decreased as compared to the distraction state. At the subsystem level, we found increased FC between the core and medial temporal lobe (MTL) subsystem as well as decreased FC between the core and dorsal medial prefrontal cortex (DMPFC) subsystem and within the MTL subsystem. Finally, subjects' behavioral measures of rumination and brooding were negatively correlated with FC between the core and DMPFC subsystems. These results suggest active rumination involves enhanced constraint by the core subsystem on the MTL subsystem and decreased coupling between the core and DMPFC subsystem, allowing for more information exchange among those involved DMN components. Furthermore, the reproducibility of our findings provides a rigorous evaluation of their validity and significance.