Probing inter-areal computations with a cellular resolution two-photon holographic mesoscope

Brain computation depends on intricately connected yet highly distributed neural networks. Due to the absence of the requisite technologies, causally testing fundamental hypotheses on inter-areal processing has remained largely out-of-each. Here we developed the first two photon holographic mesoscope, a system capable of simultaneously reading and writing neural activity patterns with near single cell resolution across large regions of the brain. We demonstrate the precise photo-activation of spatial and temporal sequences of neurons in one or multiple brain areas while reading out the downstream effect in several other regions. We thus establish mesoscale two photon holographic optogenetics as a new platform for mapping functional connectivity and causal interactions across distributed cortical areas with high resolution.