Subcellular Imaging of Voltage and Calcium Signals Reveals Neural Processing In Vivo

A mechanistic understanding of neural computation requires determining how information is processed as it passes through neurons and across synapses. However, it has been challenging to measure membrane potential changes in axons and dendrites in vivo. We use in vivo, two-photon imaging of novel genetically encoded voltage indicators, as well as calcium imaging, to measure sensory stimulus-evoked signals in the Drosophila visual system with subcellular resolution. Across synapses, we find major transformations in the kinetics, amplitude, and sign of voltage responses to light. We also describe distinct relationships between voltage and calcium signals in different neuronal compartments, a substrate for local computation. Finally, we demonstrate that ON and OFF selectivity, a key feature of visual processing across species, emerges through the transformation of membrane potential into intracellular calcium concentration. By imaging voltage and calcium signals to map information flow with subcellular resolution, we illuminate where and how critical computations arise. [Display omitted] •In vivo, two-photon imaging of novel genetically encoded voltage indicators•Observing sensory stimulus-evoked voltage signals with subcellular resolution•Calcium signals, unlike voltage signals, are compartmentalized within a neuron•ON and OFF selectivity arises in the transformation between voltage and calcium Observation of subcellular changes in membrane potential and calcium concentration using two-photon imaging of genetically encoded indicators illuminates neuronal computations in vivo, including the origin of ON and OFF selectivity.