Yoshiyuki Hirano1, Afonso C. Silva2
1Cerebral Microcirculation
Unit, Laboratory of Functional & Molecular Imaging, National Institute of
Neurological Disorders & Stroke, National Institutes of Health, Bethesda,
MD, United States; 2Cerebral Microcirculation Unit, Laboratory of
Functional & Molecular Imaging,, National Institute of Neurological
Disorders & Stroke, National Institutes of Health, Bethesda, MD, United
States
Biophysical models of BOLD contrast assume that the arterial vasculature is fully saturated with oxygen, so that BOLD originates in capillaries and veins. Here, we measured the BOLD and CBF fMRI response to somatosensory stimulation in α-chloralose anesthetized rats under different levels of arterial oxygenation. The CBF response was not affected by arterial oxygenation, while the onset time of the BOLD response in hypoxia was significantly longer than those in normoxia or hyperoxia. The onset time difference between BOLD-CBF was significantly smaller than the arteriole-venule transit time, suggesting that a measurable fraction of the BOLD response is of arterial origin.
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