The Ratio of CBF to CMRO2 Change with Brain Activation Increases with Increasing Stimulus Amplitude in Human Visual Cortex

Christine Liang¹, Beau Ances¹, Joanna Perthen¹, Joy Liau¹, Giedrius Buracas¹, Susan Hopkins¹, Richard Buxton²

A calibrated-BOLD method was used to test whether the CBF/CMRO2 coupling ratio n, defined as the ratio of the fractional changes in CBF and CMRO2 with brain activation, changes with stimulus intensity. In human visual cortex, the ratio of the CBF and BOLD responses decreased with increasing contrast of a flickering checkerboard, consistent with n increasing from ~1.7 to ~2.3. This steady increase in CBF, with a rolling off of CMRO2, may be consistent with CBF driven by the initial excitatory phase of neural activity while CMRO2 responds to the overall energy needs of the full evoked response.