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International audience; In view of the potential of global resting blood flow level to confound the interpretation of blood oxygenation level-dependent (BOLD) fMRI studies, we investigated the effect of pronounced elevation in baseline cerebral blood flow (CBF) on BOLD and CBF responses to functional activation. Twelve healthy volunteers performed bilateral finger apposition while attending to a radial yellow/blue checkerboard. Three levels of global CBF increase were achieved by inhaling 5, 7.5 or 10% CO2. CBF and BOLD signals were simultaneously quantified using interleaved multi-slice pulsed arterial spin labeling (PASL) and T2*-weighted gradient echo sequences. Increasing basal CBF produced a significant decrease in the activation-induced BOLD response, with the slope of the optimal linear fit of activation versus basal BOLD signal changes of -0.32 +/- 0.01%/% for motor and visual cortex regions of interest (ROIs). While the modulation in basal flow level also produced a statistically significant effect on the activation-induced CBF change, the degree of relative attenuation of the flow response was slight, with a slope of -0.18 +/- 0.02%/% in the motor and -0.13 +/- 0.01%/% in the visual cortex ROI. The current findings describe a strong attenuation of the BOLD response at significantly elevated basal flow levels and call for independent quantification of resting CBF in BOLD fMRI studies that involve subjects and/or conditions with markedly elevated global perfusion.

International audience; While much is known about the functional architecture of the visual system, little is known about its large-scale dynamics during perception. This study describes this dynamics with a high spatial, temporal and spectral resolution. We recorded depth EEG of epileptic patients performing a face detection task and found that the stimuli induced strong modulations in the gamma band (40 Hz to 200 Hz) in selective occipital, parietal and temporal sites, in particular the fusiform gyrus, the lateral occipital gyrus and the intra-parietal sulcus. Occipito-temporal sites were the first to be activated, closely followed by the parietal sites, while portions of the primary visual cortex seemed to deactivate temporarily. Some of those effects were found to be correlated across distant sites, suggesting that a coordinated balance between regional gamma activations and deactivations could be involved during visual perception.