To probe a potential physiological mechanism behind reported BOLD fMRI signals in white matter (WM), we compared pulse-oximetry signals measured from finger-tip photo-plethysmography (PPG) with fMRI signals recorded simultaneously during an overnight sleep study. Intermittent amplitude (AMP) drops were observed during which WM signal increased and grey matter signal decreased. These findings point to a systemic vascular contribution to WM fMRI signals, driven by AMP drops, and possibly linked to fluctuations in arousal state.
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