Time-dependent correlation of cerebral blood flow with oxygen metabolism in activated human visual cortex as measured by fMRI

The aim of this study was to investigate the relationship between relative cerebral blood flow (delta CBF) and relative cerebral metabolic rate of oxygen (delta CMRO2) during continuous visual stimulation (21 min at 8 Hz) with fMRI biophysical models by simultaneously measuring of BOLD, CBF and CBV fMRI signals. The delta CMRO2 was determined by both a newly calibrated single-compartment model (SCM) and a multi-compartment model (MCM) and was in agreement between these two models (P>0.5). The duration-varying delta CBF and dCMRO(2) showed a negative correlation with time (r=-0.97, P<0.001); i.e., delta CBF declines while delta CMRO2 increases during continuous stimulation. This study also illustrated that without properly calibrating the critical parameters employed in the SCM, an incorrect and even an opposite appearance of the flow-metabolism relationship during prolonged visual stimulation (positively linear coupling) can result. The time- dependent negative correlation between. ow and metabolism demonstrated in this fMRI study is consistent with a previous PET observation and further supports the view that the increase in CBF is driven by factors other than oxygen demand and the energy demands will eventually require increased aerobic metabolism as stimulation continues. (C) 2008 Elsevier Inc. All rights reserved.