Project Summary: We propose the development of a novel bias-switchable row-column 2D ultrasound transducer array technology for 3D ultrasound and photoacoustic imaging of whole-brain functional activity in a wearable format for awake and moving animals. These can be developed into high-frequency arrays and even transparent variants that should allow optical and ultrasonic imaging down to resolutions of 30 microns, approaching single-neuron scales. Unlike previous 2D array technologies that require wires connecting to each transducer element, our approach requires only row- and column addressing, yet permits readout from every element of the array using novel electrostrictive bias switching approaches. The technology promises first-of-it?s kind volumetric functional brain imaging of blood-flow changes, blood oxygenation changes, and even neuron activity over the whole brains of awake and moving rodents. The array offers significant potential for next-generation neuroscience experiments involving both optical and acoustic methods, including future work combining functional ultrasound and photoacoustic imaging with optogenetics, optical microscopy of genetically- encoded reporters of neuron activity, ultrasound neuro-stimulation, ultrasound blood-brain barrier disruption for drug delivery, and more. The arrays have considerable translational potential for future human subject imaging in neurosurgeries, neonates, and with potential for implantable devices for longitudinal functional brain imaging. Our research methods include careful design and fabrication of these wearable high-frequency arrays with special attention to transparent variants. We also develop novel imaging schemes and implement these schemes on programmable ultrasound systems. Testing will include array characterization, imaging phantoms, imaging cells expressing near-infrared (NIR) genetically-encoded reporters of neuron Calcium activity, and animal imaging experiments aiming to visualize functional brain imaging due to whisker stimulation. These animal experiments will be performed in both anesthetized animals. If successful, this work will set the stage for future experiments in awake moving animals.