Investigating timing of BOLD fMRI responses in individual cortical vessels to short and long stimulus durations

Motivation: Typical fMRI data observes hemodynamics from multiple vascular compartments in each voxel, however understanding the link between neuronal and vascular dynamics will require vessel-specific measurements. Goal(s): To investigate the timing and amplitude of hemodynamic responses within individual arteries and veins of the human cortex and assess how they change with stimulus duration. Approach: We applied single-vessel fMRI with multiple echoes to separate inflow and BOLD components, and distinguished intravascular and extravascular dynamics in and around arteries and veins. Results: We observed faster dynamics in arteries, and a post-stimulus undershoot in all vessels, potentially providing new insights into hemodynamics in the human brainImpact: Knowledge about hemodynamics within individual vascular compartment is provided by invasive microscopy in small-animal models, and less is known about hemodynamics in humans. Here we present vessel-specific measurements of hemodynamics in humans and reveal unexpected features in the fMRI response.