Contrast mechanisms in vessel-scale human fMRI: Ultra-slow post-stimulus “ringing” oscillations in cortical arteries

Motivation: In-vivo microscopy of brain hemodynamics have observed resonance phenomena in pial arteries in mouse cerebral cortex, however similar observations in human fMRI are anecdotal. Vessel-scale fMRI has the potential to reconcile these observations. Goal(s): Characterize arterial resonance phenomena in human pial vessels. Approach: Vessel-scale fMRI sensitive to blood velocity and vessel diameter changes to track responses of individual pial vessels to visual stimulation. Results: Reductions in inflow enhanced signal are seen in many arterial responses, suggesting a reduced velocity corresponding to increased vessel diameters. Responding vessels exhibit "post-stimulus ringing", i.e., slow oscillations (~0.1Hz) phase-locked to stimulus presentation, after the main response. Impact: We demonstrate a post-stimulus ringing phenomenon in vessel-scale fMRI responses in individual cortical arteries when responding to visual stimulation. This suggests a trial-locked oscillation that is consistent with observations of arterial resonance seen in in-vivo microscopy studies.