Researchers led by the Howard Hughes Medical Institute's Janelia Research Campus, working with Google Research and international collaborators, have released a complete wiring map of an adult male fruit fly's brain and central nervous system. The resource contains 166,391 neurons and about 125 million synaptic connections, making it the largest complete brain map yet when measured by neuron count, according to Google Research and the study published in Cell.
The map, known as a connectome, records the three-dimensional shape of neurons and the synapses through which they communicate. It includes the central brain, optic lobes and ventral nerve cord, the insect structure analogous to a vertebrate spinal cord. That wider coverage lets researchers follow sensory information from smell, vision and hearing through the brain toward circuits that control walking, flying and other movements.
Scientists created the dataset from extremely detailed electron-microscope images collected over years. Google Research algorithms assembled millions of two-dimensional images and produced initial three-dimensional neuron reconstructions, while specialists at Janelia checked and corrected the results. The team said this combination of artificial intelligence and extensive human proofreading was essential because neuron shapes are complex and automatic segmentation can join or split cells incorrectly.
The male connectome can now be compared with previously completed female maps. Researchers reported that 4.8 percent of neurons in the male brain and 2.4 percent in the female brain belonged to sex-specific cell types, while another share of male neurons formed connections that differed between sexes. These differences were concentrated in higher processing circuits, offering testable routes for studying courtship, aggression and other sex-linked behaviors rather than suggesting that the two nervous systems are broadly different.
Fruit flies are central model organisms in genetics and neuroscience because they have short life cycles, reproducible behaviors and biological mechanisms shared across animals. Scientists cannot yet map all 86 billion neurons in a human brain at comparable resolution, so smaller nervous systems provide a practical way to test how wiring produces perception, decisions and action. The public dataset can also help laboratories identify circuits before conducting targeted experiments.
The researchers have made the images, reconstructions, annotations and connectivity data available through online visualization and download tools. The map is a structural reference, not a recording of thoughts or a complete explanation of behavior, and its predictions still require experiments in living flies. Its immediate value will come from comparing individuals and sexes, linking particular circuits to behavior and improving methods that may eventually scale to larger animal nervous systems.
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