Inter-Subject Variability in the Amplitude of the Resting-State fMRI Global Signal Reflects Differences in EEG Vigilance

Chi Wah Wong¹, Valur Olafsson¹, Omer Tal¹, Thomas Liu¹

The global signal is often considered a confound in resting-state fMRI. However, a recent primate study has shown that the global signal may contain significant contributions from neural sources. In this study, we used simultaneous EEG-fMRI to examine the sources of inter-subject variability in the amplitude of the global signal in humans. We found that the global signal amplitude is negatively correlated with an EEG-based vigilance measure.