Interrogation of single-neuron functional connectivity in the cortex and hippocampus via fast cross-layer all-optical physiology

The interrogation of functional neural circuits is crucial for uncovering how the brain works during diverse behaviors. Multi-plane neurophysiological measurement systems with high temporal resolution are indispensable, especially for dissecting inter-layer functional connectivity. Here, we develop a cross-layer all-optical physiology system (CLAOP) that enables the simultaneous recording and manipulation of single-neuron activities in multiple neuronal layers, with axial intervals as large as 530 m, at high temporal resolutions. Based on spatiotemporal multiplexing, our system enables all-optical analysis with a high frame rate up to 396 Hz and minimal time delay in inter-layer imaging and photostimulation, in both the mouse cortex and hippocampus in vivo. Combined with behavioral experiments, CLAOP provides all-optical evidence linking behavioral responses to neuronal connectivity in the primary visual cortex (V1) of live mice. Furthermore, we demonstrate that CLAOP can perturb the activity response of inter-layer cortical neurons to sensory stimuli according to their functional signatures. Overall, CLAOP provides an all-optical approach for mapping inter-layer connectivity at the single-neuron level and for modifying neuronal responses in behaving animals.