Brain wiring maps
Electron-microscope and AI pipelines have mapped every neuron and synapse of whole fly brains.
Open in the interactive tree →The first connectome, the 302 neurons of the worm C. elegans, took more than a decade of manual work by Sydney Brenner's group (1986). With automated electron microscopy and AI-assisted tracing, the FlyWire consortium published the full adult fruit-fly brain in October 2024: 139,255 neurons and about 50 million synapses. A wiring diagram shows which cells talk to which, the basis for models of how circuits compute.
As of October 2026
The MICrONS consortium published a package of papers in April 2025 on a cubic millimeter of mouse visual cortex mapped at synaptic resolution, with about half a billion synapses reconstructed and the activity of about 75,000 of the neurons recorded beforehand. In September 2026 Cell published the complete connectome of the male fly central nervous system (brain plus nerve cord) from Janelia, Google and Cambridge: 166,700 neurons, produced with more than 1,000 times less time and resources than earlier whole-brain maps. A whole mouse brain has roughly 70 million neurons and remains far out of reach, and even one cubic millimeter produces petabytes of image data.
Open steps
- Automatic error correction at scale High AI leverageMachine segmentation still needs humans to fix splits and merges; proofreading a whole mouse brain by hand is out of reach.
- Faster electron microscopy Medium AI leverageOne cubic millimetre already yields petabytes and a mouse brain is roughly 500 times larger; imaging speed, tissue cutting and storage need big jumps.
- Adding synapse type and strength Medium AI leverageA wiring map lacks neurotransmitter, synapse strength and gene-expression information; combining EM with molecular imaging is needed to predict function.
- Predicting activity from wiring High AI leverageConnectome-based fly models already predict activity in parts of the brain; a whole-nervous-system model reproducing several behaviours and tested in real flies is still missing.
Where AI could help
High AI leverage. Segmentation and proofreading were the cost center and AI cut them over 1,000-fold for the fly; imaging a mouse brain is the next limit.
- Automatic neuron segmentation and synapse detection in electron microscopy
- Error finding to cut human proofreading
- Predicting neuron type and neurotransmitter from images
- Compression and storage handling of petabyte volumes
Shown so far
- On 3 September 2026 Cell published the complete male fruit-fly central nervous system connectome (over 166,000 neurons), made with AI-assisted methods the team says cut time and resources more than 1,000-fold. source
- In April 2025 the MICrONS consortium published a cubic-millimeter mouse cortex map with about 200,000 cells and 523 million synapses, reconstructed with machine-learning segmentation plus human proofreading. source
Prerequisites
- Neuron doctrine1888
- Electron microscope1931-1933Whole-brain maps are built from automated electron microscopy
- Worm connectome1986The fly maps follow the worm wiring diagram of 1986, the first complete one
- Deep Learning2012