Blood-oxygen-level-dependent (BOLD) signals can produce much faster (>0.2Hz) responses than predicted by canonical hemodynamic response models. The timing of hemodynamic responses depends on vascular anatomy, and whether these fast responses differ in veins and parenchyma is unknown. Linear models predict that with faster stimuli, venous responses should attenuate more than the parenchyma. We tested this hypothesis by imaging visual responses at high spatial resolution with 7T fMRI. We found that both veins and parenchyma produce larger fMRI responses to fast stimuli than predicted by linear models, suggesting that faster stimuli produce narrower hemodynamic responses in both compartments.
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