Electrophysiological foundations of the human default-mode network revealed by brain-wide intracranial-EEG recordings during resting-state and cognition

Abstract

Investigations using noninvasive functional magnetic resonance imaging (fMRI) have provided significant insights into the unique functional organization and profound importance of the human default mode network (DMN), yet these methods are limited in their ability to resolve network dynamics across multiple timescales. Electrophysiological techniques are critical to address these challenges, yet few studies have explored the neurophysiological underpinnings of the DMN. Here we investigate the brain-wide electrophysiological organization of the DMN in a common large-scale network framework consistent with prior fMRI studies. We used brain-wide intracranial EEG (iEEG) recordings, and evaluated intra- and cross-network interactions during the resting-state and cognition. Our analysis revealed significantly greater intra-DMN phase iEEG synchronization in the slow-wave (< 4 Hz) while DMN interactions with other brain networks was higher in all higher frequencies. Crucially, slow-wave intra-DMN synchronization was observed in the task-free resting-state and during verbal memory encoding and recall. Compared to resting-state, intra-DMN phase synchronization was significantly higher during both memory encoding and recall. Slow-wave intra-DMN phase synchronization increased during successful memory retrieval, highlighting its behavioral relevance. Finally, analysis of nonlinear dynamic causal interactions revealed that the DMN is a causal outflow network during both memory encoding and recall. Our findings identify dynamic spectro-temporal network features that allow the DMN to maintain a balance between stability and flexibility, intrinsically and during task-based cognition, provide novel insights into the neurophysiological foundations of the human DMN, and elucidate network mechanisms by which it supports cognition.

Modulating verbal working memory with fronto‐parietal transcranial electric stimulation at theta frequency: Does it work?

“…Another mechanism could potentially be that in the stronger current density under the central reference electrode location with reversed polarity might have enabled a de‐coupling of default‐mode network hubs over central areas with the fronto‐parietal working memory network. The default mode network has been associated with slow frequency coherence in the delta to alpha range (Das et al, 2020; Kim et al, 2014; Samogin et al, 2019), and more specifically, areas of the default‐mode and fronto‐parietal network have been shown to be related to theta band connectivity (Kam et al, 2019). This might also explain the absence of a modulation of response times during in‐phase tACS in our study, where we used the larger return electrode.…”

Frequency‐specific coactivation patterns in resting‐state and their alterations in schizophrenia: An fMRI study

“…If so, slow‐4 might provide more information about the dynamics of DMN, supporting that DMN has frequency‐specific properties (Park et al, 2019 ). Nevertheless, future study is needed to investigate the electrophysiological foundation of DMN (Das et al, 2020 ; Samogin et al, 2019 ).…”

Oscillatory mechanisms of intrinsic brain networks

“…Anup Das, de los Angeles, & Menon, 2020). Electrodes in temporal regions, such as superior temporal sulcus (STS) and middle temporal gyrus (MTG) consisted most of the DMN electrodes included in their study, which is highly different from our study as we focus more in medial prefrontal cortex (mPFC) and posterior cingulate cortex (PCC).…”

“…Our results suggest the active theta coupling of the DMN at rest, which may contribute to maintenance of the memory function. Interestingly, a recent study observed greater intra-DMN phase synchronization in the slow-wave (<4Hz) while greater cross-network interaction of the DMN in higher frequencies (>4Hz; Anup Das, de los Angeles, & Menon, 2020). Electrodes in temporal regions, such as superior temporal sulcus (STS) and middle temporal gyrus (MTG) consisted most of the DMN electrodes included in their study, which is highly different from our study as we focus more in medial prefrontal cortex (mPFC) and posterior cingulate cortex (PCC).…”