Intracranial neurophysiological mechanisms underlying rumination

778 

Abstract Submission 

Xiao Chen¹, Zhen Fan², Dong Chen³, Liang Wang³, Liang Chen⁴, Chao-Gan Yan¹

¹Institute of Psychology, Chinese Academy of Sciences, Beijing, Beijing, ²Department of Neurosurgery of Huashan Hospital, Shanghai, Shanghai, ³Institute of Psychology, Chinese Academy of Sciencess, Beijing, Beijing, ⁴Huashan Hospital of Fudan University, Shanghai, Shanghai

Xiao Chen  
Institute of Psychology, Chinese Academy of Sciences
Beijing, Beijing

Zhen Fan  
Department of Neurosurgery of Huashan Hospital
Shanghai, Shanghai

Dong Chen  
Institute of Psychology, Chinese Academy of Sciencess
Beijing, Beijing

Liang Wang  
Institute of Psychology, Chinese Academy of Sciencess
Beijing, Beijing

Liang Chen  
Huashan Hospital of Fudan University
Shanghai, Shanghai

Chao-Gan Yan  
Institute of Psychology, Chinese Academy of Sciences
Beijing, Beijing

Rumination is uncontrollable, self-reflective, and repetitive thinking about the distress and its possible causes and consequences (Watkins & Roberts, 2020). A wealth of studies has linked it to major depressive disorder (MDD) and indicated its pivotal role in the psychopathology of MDD (Lyubomirsky et al., 2015). Accordingly, a better understanding of its neural basis may pave the way for the next-generation treatment of MDD. Existing evidence from studies using functional magnetic resonance imaging (fMRI) has shown that brain regions of the default mode network (DMN) are involved in active rumination (Zhou et al., 2020). Our previous study further highlighted the enhanced functional connectivity between two subsystems of DMN (i.e., core subsystem and medial temporal lobe (MTL) subsystem) in the neural mechanism underlying the rumination (Chen et al., 2020). To date, no research has investigated the electrophysiological organization underlying the existing functional neuroimaging evidence. Here, leveraging the intracranial electroencephalogram (iEEG) recordings from a group of patients with epilepsy engaging in an active rumination state, we intended to delineate the electrophysiological features of two key nodes from the core subsystem (precuneus) and the MTL subsystem (parahippocampal gyrus). We hypothesized that these two regions would show different electrophysiological activity patterns during rumination as compared to the control condition.

Twenty patients with intractable epilepsy participated in this study. They had been surgically implanted with stereotactic electrodes as part of their pre-surgical assessment of seizure focus. All electrodes' placements were decided based on clinical evaluation for surgery. Participants provided written consent to participate in research and the research protocol was approved by the local Institutional Review Board. Participants were asked to finish a rumination state task. Recordings were performed at the Huashan Hospital using a standard clinical system (EEG-1200C, Nihon Kohden, Irvine, CA) with 2000 Hz sampling rate. We performed electrode localization with FieldTrip version 20221210 (Stolk et al., 2018) run in the MATLAB R2023b (The MathWorks Inc., Natick, MA, US) platform. A power spectrum was obtained by performing five-cycle Morlet wavelets at 76 logarithmically spaced frequencies ranging from 0 to 150 Hz. The log power values were then Z-scored at the channel level over all the interested conditions (rumination and distraction). Finally, the mean powers of 6 different frequency bands (delta, 1-4 Hz; theta, 4-8 Hz; alpha, 8-12 Hz; beta, 12-30 Hz; low gamma, 30-70 Hz; and high gamma, 70-150Hz) were obtained by averaging all Z-standardized power value time-series across all corresponding frequencies. A paired t-test was performed on the subject-level mean power values.

A one-way anova revealed a significant condition effect (F(4, 76) = 12.08, p < 0.001, eta2 = 0.32). Post hoc comparisons showed that participants' emotional levels after the sad memory condition were significantly lower than those before and after the resting state. Emotional levels after the rumination condition were lower than those after the distraction condition (Figure 1).

We observed a decreased low gamma and high gamma band power in the parahippocampal gyrus (low gamma: t = -2.48, p = 0.02; high gamma: t = -2.66, p = 0.02). On the contrary, enhanced delta (t = 3.81, p = 0.001), theta (t = 3.20, p = 0.02), and alpha (t = 2.70, p = 0.03) band powers were revealed in the precuneus (Figure 2).

We found dissociated power changes in the precuneus and parahippocampal gyrus during a continuous rumination state as compared to the control condition. Our results unveiled the electrophysiological mechanism underlying the functional coupling between the core and MTL subsystems of DMN during an active rumination state.

Self Processes ¹

Neurophysiology of Imaging Signals ²

Consciousness

Electroencephaolography (EEG)

ELECTROPHYSIOLOGY

Emotions

Other - intracranial electroencephalogram