Researchers announced on Friday that they had completed a map of every neuron in the central nervous system of an adult male fruit fly, a project begun in 2008 and once dismissed by many scientists as unfeasible.
Google Research and the Howard Hughes Medical Institute's Janelia Research Campus published the first complete connectome of an adult male fruit fly's entire central nervous system in the journal Cell on 3 September 2026. The work was published as a package of four papers, led by a study titled “Sexual dimorphism in the complete connectome of the Drosophila male central nervous system.”
The map covers the brain, both optic lobes and the ventral nerve cord. It records roughly 125 million synapses across 166,700 neurons, making it the largest single-animal nervous-system map ever assembled.
A connectome is a list of every neuron in a brain, including its location in three-dimensional space and the connections, known as synapses, that it forms with other neurons. The fruit fly, Drosophila melanogaster, is a key model organism in neuroscience, and the completed map could provide neurobiologists with a tool for studying how the brain works.
The connectome was completed by researchers at Janelia and computer scientists at Google. The collaboration also included the MRC Laboratory of Molecular Biology, the University of Cambridge and Google Research. Hundreds of researchers contributed over nearly two decades.
When Janelia researchers set out to map all neurons in the fruit fly brain in 2008, early estimates suggested that manual tracing with the methods then available would require around 500 people working for ten years. Building a complete picture of the hundreds of millions of synapses in a brain as small as a fruit fly’s cannot be done by people in a manageable amount of time.
The project therefore depended on new imaging and reconstruction methods. Artificial intelligence was used to combine millions of two-dimensional images into three-dimensional neural shapes, allowing researchers to reconstruct the nervous system at a scale beyond manual tracing.
The result extends a succession of increasingly detailed maps. Scientists had unveiled the connectome of the 302 neurons in C. elegans 20 years earlier. In 2020, researchers released the hemibrain, containing 25,000 neurons, then the biggest and most detailed connectome created. The 2024 FlyWire project produced a complete female brain connectome.
The new work is the first complete male connectome and the first map to cover a full brain and nerve cord in one animal. Researchers identified 262 sex-specific and 114 sexually dimorphic cell types, representing about 4.8% of the central brain.
The data are freely accessible through Neuroglancer at Janelia’s Male CNS Connectome project site. The researchers said the effort also allowed them to refine tools that are likely to be applied to more complex nervous systems, potentially including those of vertebrates.
Janelia is applying lessons from fly connectomics to efforts to build connectomes of two transparent vertebrate fish, the larval zebrafish and adult Danionella. The published work does not establish when those maps may be completed or whether the fruit fly map has already revealed new principles of neural circuits.
Comments (0)