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Abstract
Electroencephalography-correlated functional magnetic resonance imaging (EEG/fMRI)
can be used to identify blood oxygen level-dependent (BOLD) signal changes associated
with both physiological and pathological EEG events. Here, we implemented continuous
and simultaneous EEG/fMRI to identify BOLD signal changes related to spontaneous power
fluctuations in the alpha rhythm (8-12 Hz), the dominant EEG pattern during relaxed
wakefulness. Thirty-two channels of EEG were recorded in 10 subjects during eyes-closed
rest inside a 1.5-T magnet resonance (MR) scanner using an MR-compatible EEG recording
system. Functional scanning by echoplanar imaging covered almost the entire cerebrum
every 4 s. Off-line MRI artifact subtraction software was applied to obtain continuous
EEG data during fMRI acquisition. The average alpha power over 1-s epochs was derived
at several electrode positions using a Fast Fourier Transform. The power time course
was then convolved with a canonical hemodynamic response function, down-sampled, and
used for statistical parametric mapping of associated signal changes in the image
time series. At all electrode positions studied, a strong negative correlation of
parietal and frontal cortical activity with alpha power was found. Conversely, only
sparse and nonsystematic positive correlation was detected. The relevance of these
findings is discussed in view of the current theories on the generation and significance
of the alpha rhythm and the related functional neuroimaging findings.