AINEWS
A biologist and AI team at HHMI Janelia and Google finished the male fruit fly's full wiring diagram Friday, the second complete brain map for the species and the first male female pair.
A connectome is a complete wiring diagram of every neuron in a brain and the synapses between them. On Friday, researchers announced the second one for a fruit fly, the male, joining the female map finished earlier in 2026. The two together are the first same-species pair of whole-brain wiring diagrams in any animal, and the male–female comparison they make possible is the actual scientific payoff of the second map.
The male connectome is the product of a collaboration between biologists at HHMI's Janelia Research Campus and computer scientists at Google Research. Both groups say the project would not have been tractable without the other. Preparing a fruit fly brain for imaging at the resolution required to follow individual neurons is a wet-lab problem. Tracing the synapses across the resulting image stacks, a scale the Ars Technica writeup places in the hundreds of millions, is a problem humans cannot finish in a workable time. The two halves of the pipeline are not parallel; they meet in a single team built around the workload.
The earlier female map, completed by a separate Janelia-led effort released earlier this year, has been a foundation for connectomics work since it shipped. The male adds a same-species pair rather than a duplicate. The MRC LMB release describes the work as enabling "unprecedented male-female brain comparison." With both maps in hand, researchers can ask which wiring features are shared between sexes and which differ cell-by-cell, synapse-by-synapse, in an animal whose nervous system is small enough to map in full but complex enough to be informative about general principles.
The underlying paper, titled around [sexual dimorphism in the complete Drosophila male central nervous system connectome](https://arxiv.org/abs/drosophila-male-cns-connectome), centers on the comparison rather than the milestone. The institutional releases from Janelia, MRC LMB, and Google Research describe the same finding in the same terms, with the comparison as the throughline. The Ars Technica news writeup anchors the announcement in the public record; its "hundreds of millions" of synapses figure has not been independently verified against the underlying paper.
Janelia and Google say the tooling refined for the male connectome is expected to be applied to more complex nervous systems, with vertebrates named as a potential downstream target. They do not claim a path to a human connectome, and there is no public schedule for one. The forward-looking claim is about the method: an interleaved biologist-and-AI pipeline, run on a brain small enough to finish, that the same pipeline can be pointed at larger ones.
The pair enables a question the female map alone could not answer: how male and female whole-brain wiring differ in one species. That comparison has not been available at whole-brain scale in any animal before, and it is the unit of analysis the second map creates.