Biological systems operate across distributed regions with fast, localized dynamics, yet existing biointerfaces fail short in providing both high spatiotemporal precision and the ability to dynamically target any region without disturbing surrounding tissue. Here, we present an deep-tissue light source based on focused ultrasound (FUS) scanning of mechanoluminescent nanotransducers (MLNTs) circulating through the vasculature. We demonstrate the programmability of this approach in tissue-mimicking phantoms and the endogenous circulatory system of animals, where tunable spatial resolution and dynamic light patterning can be achieved. We validate the functionality of the ultrasound-scanning light source in opsin-expressing neurons through electrophysiological recordings and immunostaining. We showcase dynamic three-dimensional brain targeting and temporally resolved behavioral control in freely moving animals via the ultrasound-scanning light source. This non-invasive deep-tissue light source offers a versatile strategy for body-wide optical interfacing.