The organization of visual pathways in the Drosophila brain

Visual systems transform photoreceptor inputs into rich perceptual representations through hierarchical networks that extract features along parallel pathways. Although this architecture is conserved across species, how visual information is routed throughout an entire brain remains elusive in any animal. Using the male Drosophila connectome, we trace signals from photoreceptors through the optic lobes-layered, retinotopic regions containing two-thirds of the brain's neurons-and onward into the central brain. Network-based analyses reveal a multilayered architecture of pathway classes with distinct input mixtures. Signals from visual-input channels spread broadly yet converge in focal regions apparently specialized for particular features and fine spatial sampling. Predictions of receptive-field structure and feature-related input biases are consistent with physiological data and extend to thousands of uncharacterized neuron types. These analyses provide a neuron-by-neuron account of how a visual system organizes and integrates information across an entire brain.