Hemodynamic Correlates of Electrophysiological Activity in the Default Mode Network

Alpha oscillations (8–13 Hz) are the dominant electrophysiological rhythms during resting state and correlate more strongly than other frequency bands with blood oxygen-level dependent (BOLD) signals in default mode network (DMN) regions. Using simultaneously collected high-density EEG and fMRI data from 20 healthy volunteers at rest, the authors detected the DMN from source-reconstructed EEG data across multiple frequency bands and mapped correlations between EEG-derived DMN activity and fMRI-BOLD signals voxel by voxel. The correlation map for alpha oscillations overlapped with DMN regions more than maps for other bands did, supporting a primary role of alpha oscillations in DMN functioning. Simultaneous EEG-fMRI is suggested as a tool for investigating human brain networks.

Study at a glance

Abstract

Hemodynamic fluctuations in the default mode network (DMN), observed through functional magnetic resonance imaging (fMRI), have been linked to electrophysiological oscillations detected by electroencephalography (EEG). It has been reported that, among the electrophysiological oscillations, those in the alpha frequency range (8–13 Hz) are the most dominant during resting state. We hypothesized that DMN spatial configuration closely depends on the specific neuronal oscillations considered, and that alpha oscillations would mainly correlate with increased blood oxygen-level dependent (BOLD) signal in the DMN. To test this hypothesis, we used high-density EEG (hdEEG) data simultaneously collected with fMRI scanning in 20 healthy volunteers at rest. We first detected the DMN from source reconstructed hdEEG data for multiple frequency bands, and we then mapped the correlation between temporal profile of hdEEG-derived DMN activity and fMRI–BOLD signals on a voxel-by-voxel basis. In line with our hypothesis, we found that the correlation map associated with alpha oscillations, more than with any other frequency bands, displayed a larger overlap with DMN regions. Overall, our study provided further evidence for a primary role of alpha oscillations in supporting DMN functioning. We suggest that simultaneous EEG–fMRI may represent a powerful tool to investigate the neurophysiological basis of human brain networks.