Electrophysiological signatures of resting state networks in the human brain

Abstract

Functional neuroimaging and electrophysiological studies have documented a dynamic baseline of intrinsic (not stimulus- or task-evoked) brain activity during resting wakefulness. This baseline is characterized by slow (<0.1 Hz) fluctuations of functional imaging signals that are topographically organized in discrete brain networks, and by much faster (1-80 Hz) electrical oscillations. To investigate the relationship between hemodynamic and electrical oscillations, we have adopted a completely data-driven approach that combines information from simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Using independent component analysis on the fMRI data, we identified six widely distributed resting state networks. The blood oxygenation level-dependent signal fluctuations associated with each network were correlated with the EEG power variations of delta, theta, alpha, beta, and gamma rhythms. Each functional network was characterized by a specific electrophysiological signature that involved the combination of different brain rhythms. Moreover, the joint EEG/fMRI analysis afforded a finer physiological fractionation of brain networks in the resting human brain. This result supports for the first time in humans the coalescence of several brain rhythms within large-scale brain networks as suggested by biophysical studies.

Fig. 1.

Example of two ICs separated by ICA from a single-subject fMRI data set. Sagittal, coronal and axial functional maps, are shown, along with the related BOLD signal in time and frequency domains. Brain areas are respectively colored in yellow-orange or in azure-blue in case of positive and negative correlation with the IC waveform.

Fig. 2.

Cortical representation of the six RSNs. For each RSN. (Left) Lateral and medial views of left hemisphere. (Center) Dorsal view. (Right) Lateral and medial views of right hemisphere.

Fig. 3.

Association between EEG rhythms and fMRI RSNs. (Left) Sagittal, coronal, and axial spatial maps of the six RSNs. (Right) Bar plots of the average correlations between the brain oscillatory activity in the delta, theta, alpha, beta, and gamma bands, and the RSN time courses.