Validating the Physiological Assumptions Made in Hyperoxia Calibrated BOLD

Paula L. Croal¹, Emma L. Hall¹, Ian D. Driver¹, Penny A. Gowland¹, Susan T. Francis¹

Hyperoxia calibrated BOLD relies on the assumption that hyperoxia has no significant effects on neuronal activity or associated CBF and aCBV. The effect of isocapnic hyperoxia on resting state activity was assessed by use of PC-MRA, LLEPI FAIR ASL and MEG. A small non-significant decrease was observed in CBF and aCBV suggestive that previously observed reductions were dominated by hypocapnia. A small focal reduction in neural oscillatory power was observed in the visual cortex, however it is contrast to the much larger global reduction observed with hypercapnia and so is unlikely to have a significant effect of neuronal activity.