Combined Electrophysiology and Functional Ultrasound Imaging: Opportunities, Challenges and Future Directions

Functional Ultrasound Imaging (fUSi) offers the ability to monitor brain mesoscale hemodynamics with high spatiotemporal resolution (100 micrometers, 200 milliseconds) across a field of view that includes both cortical and subcortical structures. Notably, it can be integrated with cellular resolution techniques such as electrophysiology and optical imaging in freely behaving animals, enabling the study of neurovascular interactions across various brain states and regions within the same subject. The combination of fUSi with electrophysiology has the potential to initiate a paradigm shift in systems neuroscience, contingent upon the reliable establishment of the neural underpinnings of the fUS signal. In this paper, we review the significant milestones in functional ultrasound over the past decade and discuss the opportunities, as well as the technological and conceptual challenges that lie ahead. We also propose future directions for functional ultrasound imaging studies, particularly focusing on freely behaving and head-fixed animals.