Genetically encoded voltage indicators (GEVIs) are light-emitting proteins that report neuronal action potentials with high spatiotemporal precision, but they have limitations, including the fact that their kinetics are too fast for typical two-photon laser scanning microscopy. Improvements to GEVI brightness, responsivity, wavelengths, and localization would facilitate action potential detection, as would enhanced imaging capabilities that are matched to the properties of specific GEVIs of interest. Lin’s team proposes to integrate the above-mentioned GEVI improvements with development of a new generation of multiphoton optical hardware that will dramatically accelerate targeted scanning, enabling high-speed imaging of hundreds of individual, genetically-defined neurons. The group will apply these improved technologies to study patterns of fast neuronal activity in vivo, during behavior. This project could enable new insights into neural circuit function in health and disease.