Laminar differences in functional oxygen metabolism in monkey visual cortex measured with calibrated fMRI.

Blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD fMRI) of cortical layers relies on the hemodynamic response and is biased toward large veins on the cortical surface. Functional changes in the cerebral metabolic rate of oxygen (ΔCMRO) may reflect neural cortical function better than BOLD fMRI, but it is unknown whether the calibrated BOLD model for functional CMRO measurement remains valid at high resolution. Here, we measure laminar ΔCMRO elicited by visual stimulation in macaque primary visual cortex (V1) and find that ΔCMRO peaks in the middle of the cortex, in agreement with autoradiographic measures of metabolism. ΔCMRO values in gray matter are similar as found previously. Reductions in CMRO are associated with veins at the cortical surface, suggesting that techniques for vein removal may improve the accuracy of the model at very high resolution. However, our results show feasibility of laminar ΔCMRO measurement, providing a physiologically meaningful metric of laminar functional metabolism.