Blood volume sensitive laminar fMRI with VASO in human hippocampus: Capabilities of clinical 7T and biophysical challenges

Motivation: The hippocampus is a challenging target for laminar fMRI. While GE BOLD-based sequences have demonstrated the feasibility of mesoscale recordings in hippocampus, the bias towards draining veins compromises the signal specificity. Goal(s): To mitigate the macrovasculature contribution, we aimed to optimize VASO to capture mesoscale sub-regional activity without sensitivity of draining veins. Approach: By evaluating a series of advanced acquisition strategies targeted to the hippocampus, we ultimately obtained improved VASO signal quality with minimal artifacts. The final protocol was subsequently validated with an autobiographical memory task. Results: We show that sub-millimeter VASO can be successfully applied to localize cognitive functions in the hippocampus. Impact: Our preliminary results indicate that mesoscale VASO collected using conventional 7T scanners can capture functional activity changes in hippocampus, providing a groundwork for future investigations of underlying neuronal circuitry of higher-order cognitive functions and their alterations in neurodegeneration.