Functional imaging of the visual cortex with bold-contrast MRI: Hyperventilation decreases signal response

Hypocapnia due to hyperventilation reduces cerebral blood flow and volume, To investigate the effects of hyperventilation on the regional signal respo nse to visual activation using blood oxygenation level-dependent (BOLD) mag netic resonance imaging (MRI), six volunteers were investigated during visu al stimulation under normocapnia and hypocapnia conditions. Hyperventilatio n significantly decreased in visual cortex the BOLD MRI response to visual stimulation (3.97 +/- 0.5% [mean ( SD) in normocapnia vs, 0.77 +/- 0.7% in hypocapnia, P < 0.01]. In three of six subjects, functional signal changes were reduced to noise level. The reduced stimulus response during hypervent ilation is probably due to a decreased overshoot in the blood oxygenation r esponse, These results indicate(2)that BOLD-contrast functional MRI is high ly sensitive to pCO changes. Magn Reson Med 41:213-216, 1999. (C) 1999 Wile y-Liss, Inc.