Neurons are signal processors: individual units that receive, compute, and transmit information within neural networks. Neurons are also cells: complex, self-organizing systems composed of billions of macromolecules in constant motion. We aim to bridge the gap between systems neuroscience and cell biology to understand how diverse neuronal processing properties emerge from dynamic molecular interactions in vivo. To that end, we employ sophisticated imaging and genetic techniques to simultaneously measure and manipulate neuronal activity and subcellular elements within well-defined Drosophila motion vision circuits. In particular, we study how organelles — specifically, mitochondria and the endoplasmic reticulum — respond to physiological neuronal activity in vivo and, in turn, tune neuronal computations. We explore uncharted territory in the field of neuroscience, linking molecular and cellular dynamics to large-scale neural circuit function in vivo.