Multiphoton Neurophotonics: Recent Advances in Imaging and Manipulating Neuronal Circuits.

The possibility of using light to image and manipulate neuronal activity, at the heart of Neurophotonics, has provided new irreplaceable tools to study brain function. In particular, the combination of multiphoton microscopy and optogenetics allows researchers to interact with neuronal circuits with single-cell resolution in living brain tissues. However, significant optical challenges remain to empower new discoveries in Neuroscience. This Review focuses on three critical areas for future development: (1) expanding imaging and optogenetic stimulation to larger fields of view and faster acquisition speeds, while maintaining single-cell resolution and minimizing photodamage; (2) enabling access to deeper brain regions to study currently inaccessible neuronal circuits; and (3) developing optical techniques for studying natural behaviors in freely moving animals. For each of these challenges, we review the current state-of-the-art and suggest future directions with the potential to transform the field.