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 across a field of view encompassing both cortical and subcortical structures. Notably, it can be integrated with cellular resolution techniques such as electrophysiology (ephys) 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 (ephys) can initiate a paradigm shift in systems neuroscience, contingent upon the reliable establishment of the neural underpinnings of the fUSi signal. In this paper, we review the significant milestones in fUSi over the past decade, describe the implementation of combined fUSi-ephys recordings, and discuss the opportunities as well as the technological and conceptual challenges that lie ahead. We also propose future directions for fUSi studies, mainly centered on freely behaving and head-fixed animals.