Multiplexed temporally focused light shaping through a GRIN lens for precise in-depth optogenetic photostimulation

In the past 10 years, the use of light has become irreplaceable for the optogenetic study and control of neurons and neural circuits. Optical techniques are however limited by scattering and can only see through a depth of few hundreds {micro}m in living tissues. GRIN lens based micro-endoscopes represent a powerful solution to reach deeper regions. In this work we demonstrate that cutting edge optical methods for the precise photostimulation of multiple neurons in three dimensions can be performed through a GRIN lens. By spatio-temporally shaping a laser beam in the two-photon regime we project several tens of targets, spatially confined to the size of a single cell, in a volume of 150x150x400 m3. We then apply such concept to the optogenetic stimulation of multiple neurons simultaneously in vivo in mice. Our work paves the way for an all-optical investigation of neural circuits at previously unattainable depths.