SummaryDrosophila melanogaster has a rich repertoire of innate and learned behaviors. Its 100,000-neuron brain is a large but tractable target for comprehensive neural circuit mapping. Only electron microscopy (EM) enables complete, unbiased mapping of synaptic connectivity; however, the fly brain is too large for conventional EM. We developed a custom high-throughput EM platform and imaged the entire brain of an adult female fly at synaptic resolution. To validate the dataset, we traced brain-spanning circuitry involving the mushroom body (MB), which has been extensively studied for its role in learning. All inputs to Kenyon cells (KCs), the intrinsic neurons of the MB, were mapped, revealing a previously unknown cell type, postsynaptic partners of KC dendrites, and unexpected clustering of olfactory projection neurons. These reconstructions show that this freely available EM volume supports mapping of brain-spanning circuits, which will significantly accelerate Drosophila neuroscience.Video Abstract

2 SUMMARY (150 words) 21Drosophila melanogaster has a rich repertoire of innate and learned behaviors. Its 100,000-22 neuron brain is a large but tractable target for comprehensive neural circuit mapping. Only 23 electron microscopy (EM) enables complete, unbiased mapping of synaptic connectivity; 24 however, the fly brain is too large for conventional EM. We developed a custom high-throughput 25 EM platform and imaged the entire brain of an adult female fly. We validated the dataset by 26 tracing brain-spanning circuitry involving the mushroom body (MB), intensively studied for its 27 role in learning. Here we describe the complete set of olfactory inputs to the MB; find a new cell 28 type providing driving input to Kenyon cells (the intrinsic MB neurons); identify neurons 29 postsynaptic to Kenyon cell dendrites; and find that axonal arbors providing input to the MB 30 calyx are more tightly clustered than previously indicated by light-level data. This freely available 31 EM dataset will significantly accelerate Drosophila neuroscience. 32 33 KEYWORDS 34Electron microscopy, connectomics, neural circuits, Drosophila melanogaster, mushroom body, 35 olfaction, image stitching 36 37 HIGHLIGHTS 38 -A complete adult fruit fly brain was imaged, using electron microscopy (EM) 39 -The EM volume enables brain-spanning mapping of neuronal circuits at the synaptic level 40 -Olfactory projection neurons cluster more tightly in mushroom body calyx than expected from 41 light-level data 42

Microstimulation of direction columns in the middle temporal visual area (MT, or V5) provides a powerful tool for probing the relationship between cortical physiology and visual motion perception. In the current study we obtained "veridical" reports of perceived motion from rhesus monkeys by permitting a continuous range of possible responses that mapped isomorphically onto a continuous range of possible motion directions. In contrast to previous studies, therefore, the animals were freed from experimenter-imposed "categories" that typify forced choice tasks. We report three new findings: (1) MT neurons with widely disparate preferred directions can cooperate to shape direction estimates, inconsistent with a pure "winner-take-all" read-out algorithm and consistent with a distributed coding scheme like vector averaging, whereas neurons with nearly opposite preferred directions seem to compete in a manner consistent with the winner-take-all hypothesis, (2) microstimulation can influence direction estimates even when paired with the most powerful motion stimuli available, and (3) microstimulation effects can be elicited when a manual response (instead of our standard oculomotor response) is used to communicate the perceptual report.