During the past decade, reproducible connectivity patterns of brain activity during rest have been identified and thoroughly investigated using PET and fMRI (Gusnard & Raichle, 2001; Raichle et al., 2001; Greicius et al., 2003). However, little is still known about the electrophysiological correlates of structured BOLD fluctuations and correlations detected during resting state.
In the presented study, we demonstrate with MEG source imaging a possible electrophysiological mechanism underlying resting-state BOLD fluctuations. Our approach is based on the hypothesis of cross-frequency coupling as a vehicle of communication and integration between and within brain regions (Steriade, 2006). As such, this mechanism represents an ideal candidate to support the resting-state networks that have been shown to match some of the major anatomical connectivity pathways across the whole brain.
We were able to identify patterns of phase-amplitude coupling between low-frequency bands and high-gamma oscillations, which reveal the regions connected during resting-state. Overall, our results suggest that the mechanisms underlying the brain's resting-state networks as detected with fMRI are based on the cross-frequency coupling between the phase of low-frequency components and the amplitude of high-gamma oscillatory fluctuations.