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Vision provides animals with detailed information about their surroundings, conveying diverse features such as color, form, and movement across the visual scene. Computing these parallel spatial features requires a large and diverse network of neurons, such that in animals as distant as flies and humans, visual regions comprise half the brain's volume. These visual brain regions often reveal remarkable structure-function relationships, with neurons organized along spatial maps with shapes that directly relate to their roles in visual processing. To unravel the stunning diversity of a complex visual system, a careful mapping of the neural architecture matched to tools for targeted exploration of that circuitry is essential. Here, we report a new connectome of the right optic lobe from a male Drosophila central nervous system FIB-SEM volume and a comprehensive inventory of the fly's visual neurons. We developed a computational framework to quantify the anatomy of visual neurons, establishing a basis for interpreting how their shapes relate to spatial vision. By integrating this analysis with connectivity information, neurotransmitter identity, and expert curation, we classified the ~53,000 neurons into 727 types, about half of which are systematically described and named for the first time. Finally, we share an extensive collection of split-GAL4 lines matched to our neuron type catalog. Together, this comprehensive set of tools and data unlock new possibilities for systematic investigations of vision in Drosophila , a foundation for a deeper understanding of sensory processing.

The neural circuits responsible for animal behavior remain largely unknown. We summarize new methods and present the circuitry of a large fraction of the brain of the fruit fly Drosophila melanogaster . Improved methods include new procedures to prepare, image, align, segment, find synapses in, and proofread such large data sets. We define cell types, refine computational compartments, and provide an exhaustive atlas of cell examples and types, many of them novel. We provide detailed circuits consisting of neurons and their chemical synapses for most of the central brain. We make the data public and simplify access, reducing the effort needed to answer circuit questions, and provide procedures linking the neurons defined by our analysis with genetic reagents. Biologically, we examine distributions of connection strengths, neural motifs on different scales, electrical consequences of compartmentalization, and evidence that maximizing packing density is an important criterion in the evolution of the fly's brain., Competing Interests: LS, CX, ZL, ST, KH, GH, KS, SB, JC, PH, WK, LU, TZ, DA, JB, TD, DK, TK, KK, NN, DO, HO, ET, MI, AB, JG, TW, RS, PS, EN, CK, CA, DB, SB, JB, BC, NC, MC, MD, OD, BE, KF, SF, NF, AF, GH, EJ, SK, NK, JK, SL, AL, CM, EM, SM, CM, MN, OO, NO, CO, NP, CP, TP, EP, EP, NR, CR, MR, JR, SR, MS, AS, AS, AS, CS, KS, NS, MS, AS, JS, ST, IT, DT, ET, TT, JW, TY, JH, FL, RP, PR, VJ, MC, GJ, KI, SS, RG, IM, GR, HH, SP No competing interests declared, MJ, JM, TB, LL, PL, LL, VJ is an employee of Google., (© 2020, Scheffer et al.)