A connectomics milestone: Mapping the complete male fruit fly brain

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Connectomics — mapping every neuron and synapse in a nervous system at cellular resolution — reached its most ambitious milestone yet. The male Drosophila melanogaster brain and central nervous system is now fully mapped: 166,000 neurons and 125 million synaptic connections, published in Cell by HHMI Janelia Research Campus and Google Research after a decade of collaboration. This map extends beyond previous connectomes by including the ventral nerve cord (the fly equivalent of a spinal cord), enabling researchers to trace connections from sensory inputs — auditory, visual, olfactory — all the way through to motor outputs. The prior female Drosophila brain connectome exists but lacked this spinal-cord analog, making direct sex-difference comparisons in circuit architecture now possible. AI was central to the reconstruction: machine learning pipelines segmented neurons from high-resolution electron microscopy imaging, with teams at HHMI Janelia then manually proofreading the results. The dataset is publicly available and navigable via Neuroglancer, Google's open-source tool for visualizing large multidimensional neural datasets. For the AI field, this represents both a product of AI methods (reconstruction) and a resource for AI research: ground-truth neural circuit data at full-organism scale, with verified annotations, usable for training computational neuroscience models and studying how brains encode and process information.