Plate Nº 23 · recorded October 10, 2026
Neuroscience & MindReported finding
Scientists Map Every Connection in a Male Fruit Fly Brain
Researchers publish the first complete wiring map of a male fruit fly brain, tracing 166,700 neurons and 124 million synapses in a nervous system no bigger than a poppy seed.
By Nathan Brooks3 min read612 words
In brief
- First complete connectome of a full central nervous system covers 166,700 neurons and 124 million synapses in one male fruit fly
- About 95% of cells are shared between male and female flies; the remaining 5% differ in cell type and wiring
- The male's central nervous system was cut into 66 blocks and imaged by seven electron microscopes running for about a year
- Published in Cell; co-led by MRC LMB, Janelia Research Campus, the University of Cambridge, Google Research, and the Champalimaud Foundation
- Findings aim to link genetic variation to circuit differences relevant to disorders such as autism and schizophrenia
A wiring map with 124 million connections
A team has published the first complete wiring map of a male fruit fly's central nervous system — 166,700 neurons and 124 million synapses in a brain no bigger than a poppy seed.
The connectome — a term for a complete diagram of neural connections — appears today in the journal Cell. It traces every link between neurons in the brain and in the ventral nerve cord, the insect equivalent of a human spinal cord.
What did the team find?
About 95% of cells appear identical between male and female flies. The remaining 5% differ in cell type and wiring. The team says those differences likely drive sex-specific behaviours such as male courtship and female egg laying.
Dr Greg Jefferis, a senior author at the MRC Laboratory of Molecular Biology, said the map opens a path to a long-standing question: "Understanding how genetic differences translate into differences in brain wiring and behaviour should eventually help us to understand how brains differ, which in such cases, including autism and schizophrenia, have a strong genetic basis."
How did they build it?
Technicians removed the central nervous system from a single adult male Drosophila melanogaster and cut it into 66 blocks. They shaved each block into layers about one ten-thousandth the width of a human hair, then imaged every cross-section with electron microscopes. Seven microscopes ran continuously for about a year to capture the full volume. Machine-learning algorithms stitched the resulting images into a three-dimensional model, which human annotators then labelled cell by cell.
What can scientists do with the data?
Joint first author Dr Philipp Schlegel, based at the MRC Laboratory of Molecular Biology and the University of Cambridge, said: "This full wiring diagram has massive potential — we've produced data that will enable all sorts of new studies into how the whole nervous system works to control behaviours."
Researchers can now trace complete circuits from sensory input to motor output — for instance, from the eyes to the legs. They can test how a single gene alters a specific synapse, or how a sex-specific neuron modifies a courtship display. Joint first author Dr Isabella Beckett said the team can now quantify how sex-specific cells and distinct wiring separate male from female fly brains, and called the data a launch pad for tracing how genes shape those differences.
Who built the connectome?
Five groups co-led the project: Jefferis's group at the MRC Laboratory of Molecular Biology, the Howard Hughes Medical Institute's Janelia Research Campus, the Drosophila Connectomics Group at the University of Cambridge's Department of Zoology, Google Research, and the Champalimaud Foundation in Portugal.
Why start with a fruit fly?
Drosophila shares many genes and circuit principles with humans, but its brain is small enough to map completely with current tools. The connectome gives researchers a reference for what a full nervous system looks like and a test bed for connectomics methods.
What are the limits?
The map describes a single male, so natural variation between individuals remains unknown. Connectomics captures structure rather than electrical activity; functional recordings are still needed to identify which connections fire and when. Cell-type definitions can also vary between labs.
What's next?
Researchers plan to compare the male diagram with a female fly connectome, now under construction, to pinpoint the exact circuits that distinguish the sexes. Methods refined for Drosophila — from nanometre slicing to AI stitching — should accelerate projects targeting larger brains.
The study received funding from UKRI Medical Research Council, the Wellcome Trust, the Howard Hughes Medical Institute, Boehringer Ingelheim Fonds, Cambridge Commonwealth, and the European and International Trust.
via UKRI News (Source)
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