Intra- and extra-cranial effects of transient blood pressure changes on brain near-infrared spectroscopy (NIRS) measurements

► We recorded NIRS from the visual cortex during pattern-reversal stimulation. ► Transient blood pressure changes were induced by arm-raising. ► Blood pressure changes significantly altered deep and shallow NIRS recordings. ► The effect appears to originate from both intra- and extra-cranial regions. ► Blood pressure must be considered as a potential confound in NIRS studies.