Resting-state functional magnetic resonance imaging (rsfMRI) has been widely
used for studying the (presumably) awake and alert human brain. Although rsfMRI
scans are typically collected while individuals are instructed to focus their
eyes on a fixation cross, objective and verified experimental measures to
quantify degree of alertness (e.g., vigilance) are not readily available.
Concurrent electroencephalography and fMRI (EEG-fMRI) measurements are also
widely used to study human brain with high spatial/temporal resolution. EEG is
the modality extensively used for estimating vigilance during eyes-closed
resting state. On the other hand, pupil size measured using an eye-tracker
device could provide an indirect index of vigilance. In this study, we
investigated whether simultaneous multimodal EEG-fMRI combined with eye-tracker
measurements can be used to determine EEG signal feature associated with pupil
size changes (e.g., vigilance measure) in healthy human subjects (n=10) during
brain rest with eyes open. We found that EEG frontal and occipital beta power
(FOBP) correlates with pupil size changes, an indirect index for locus
coeruleus activity implicated in vigilance regulation (r=0.306, p<0.001).
Moreover, FOBP also correlated with heart rate (r=0.255, p<0.001), as well as
several brain regions in the anti-correlated network, including the bilateral
insula and inferior parietal lobule. These results support the conclusion that
FOBP is an objective measure of vigilance in healthy human subjects