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Abstract
Resting-state functional connectivity studies with fMRI showed that the brain is intrinsically
organized into large-scale functional networks for which the hemodynamic signature
is stable for about 10s. Spatial analyses of the topography of the spontaneous EEG
also show discrete epochs of stable global brain states (so-called microstates), but
they remain quasi-stationary for only about 100 ms. In order to test the relationship
between the rapidly fluctuating EEG-defined microstates and the slowly oscillating
fMRI-defined resting states, we recorded 64-channel EEG in the scanner while subjects
were at rest with their eyes closed. Conventional EEG-microstate analysis determined
the typical four EEG topographies that dominated across all subjects. The convolution
of the time course of these maps with the hemodynamic response function allowed to
fit a linear model to the fMRI BOLD responses and revealed four distinct distributed
networks. These networks were spatially correlated with four of the resting-state
networks (RSNs) that were found by the conventional fMRI group-level independent component
analysis (ICA). These RSNs have previously been attributed to phonological processing,
visual imagery, attention reorientation, and subjective interoceptive-autonomic processing.
We found no EEG-correlate of the default mode network. Thus, the four typical microstates
of the spontaneous EEG seem to represent the neurophysiological correlate of four
of the RSNs and show that they are fluctuating much more rapidly than fMRI alone suggests.
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