Changes in baseline cerebral blood flow in humans do not influence regional cerebral blood flow response to photic stimulation

The effect of changes in baseline regional cerebral blood flow (rCBF) value s on the cerebral blood flow response during neuronal activation was studie d with functional magnetic resonance imaging (fMRI). Using a breath-holding challenge as a hypercapnic stimulus, rCBF alterations during photic stimul ation under normo- and hypercapnia were determined in nine volunteers. With breath-holding, baseline rCBF in areas corresponding to the visual cortex significantly increased from 54 +/- 5 ml/100 g/min to 85 +/- 9 ml/100 g/min (P < 0.001). Despite this significant change in baseline flow values, the rCBF increase during visual stimulation was very similar under normo- and h ypercapnic conditions (28 +/- 8 ml/100 g/min versus 26 +/- 8 ml/100 g/min, respectively). This study supports the notion that within wide physiologic variations, task-induced cerebral blood flow changes are independent of bas eline rCBF values. (C) 2000 Wiley-Liss, Inc.