On September 3, Cell published the complete connectome of the male fruit fly central nervous system. The map covers the brain, both optic lobes and the ventral nerve cord, the insect counterpart of the spinal cord. The published abstract counts 166,700 neurons, all proofread and annotated, sorted into 11,710 types. Google Research puts the synaptic connections at about 125 million and calls it the largest brain map to date by neuron count. Janelia says the data and the tools to explore it are free to researchers worldwide.
The map is called MaleCNS. Janelia’s FlyEM team led it with the MRC Laboratory of Molecular Biology, the University of Cambridge and Google Research. Janelia imaged the tissue with focused ion beam scanning electron microscopy. Google’s software segmented the images, tracing each neuron through the three-dimensional volume. Expert teams at Janelia and Cambridge then proofread the tracing and labeled the neurons, connections and cell types.
The project began under doubt. Gerry Rubin assembled the team in 2008, when the only finished connectome belonged to the roundworm, whose 302 neurons had taken more than a decade of manual work. Rubin recalls critics who expected a fly wiring diagram to be an uninterpretable tangle. His early estimate for proofreading computer vision output was 2,000 person-years.
Computer vision closed the gap. Viren Jain worked at Janelia from 2011 to 2014, then moved to Google and joined its Connectomics team, where the fly was the first project. The flood-filling network starts at one pixel and uses a convolutional neural network to find every other pixel in the same neuron. Google says its methods cut proofreading cost and effort by a factor of 20. Janelia says imaging and AI together reduced the resources needed for a whole-brain connectome by more than 1,000-fold. Both figures come from the institutions that built the tools.
Until now every fruit fly brain connectome came from a female. The abstract reports 8,069 neuron types shared by both sexes, 138 present in both but wired differently, 289 found only in the male and 71 found only in the female. Sex-specific and dimorphic neurons concentrate in higher brain centers, while the sensory and motor periphery is largely alike.
The counts moved between versions. The earlier abstract on Google’s publication page gives 166,691 neurons and 11,691 types. The Cell version is the one to cite, under DOI 10.1016/j.cell.2026.08.015.
Because the dataset includes the nerve cord, researchers can follow a pathway from sensory neuron to motor neuron inside one dataset. Greg Jefferis of the LMB and Cambridge described it as getting from eyes to legs in one go. Three companion papers released the same day apply the map to vision, taste and social behavior.
The day after release, a Georgia Tech graduate student posted a demonstration in which the connectome drove a character in Minecraft. 404 Media, as relayed by AI Weekly, reported millions of views within a day. A daily.dev summary describes such demos as approximations that add guessed signal strengths and trained translators to the wiring. A connectome records which neurons contact which. It carries no biochemistry.
The next full brain is the larval zebrafish, in a collaboration with Harvard. Google says mapping the 86 billion neurons of a human brain is not yet possible. The largest human sample the team has reconstructed holds 50,000 cells and 150 million synapses, about 1.4 petabytes of data.
