Abstract
How the brain perceives sensory information and generates meaningful behavior depends critically on its underlying circuitry. The protocerebral bridge (PB) is a major part of the insect central complex (CX), a pre-motor center may be analogous to the human basal ganglia. Here, by deconstructing hundreds of PB single neurons and reconstructing them into a common 3D framework, we have constructed a comprehensive map of PB circuits with labeled polarity and predicted directions of information flow. Our analysis reveals a highly-ordered information processing system that involves directed information flow among CX subunits through 194 distinct PB neuron types. Circuitry properties such as mirror, convergence, divergence, tiling, reverberation and parallel signal propagation were observed; their functional and evolutional significances were discussed. This layout of PB neuronal circuitry may provide guidelines for further investigations on transformation of sensory (e.g. visual) input into locomotion command in fly brains.