Scientists have mapped more than 166,000 neurons of a male fruit fly’s central nervous system, creating a complete structural wiring diagram that mirrors a 2024 female map. Published in Cell and Current Biology, the new connectome allows researchers to directly compare male and female brains to pinpoint the biological drivers of sex-specific behaviors like mating and aggression.
A fruit fly brain is roughly the size of a poppy seed, yet its microscopic architecture packs extraordinary complexity. The resulting connectome charts more than 166,000 neurons, offering the scientific community an unprecedented look at how an insect nervous system is wired.
The HHMI Janelia Research Campus and Google Research Collaboration
This massive mapping effort represents years of painstaking work carried out through a partnership between the Howard Hughes Medical Institute’s Janelia Research Campus, Google Research, and international collaborators. Artificial intelligence played a critical role in the project, helping researchers scale up the demanding process of tracing and reconstructing neural connections.
Having both datasets side by side gives neuroscientists a complete comparative toolkit for the first time.
“It is the first time we can compare both sexes of an animal with complex social behavior. Male and female flies have a lot of differences in their behavior, and neuroscientists want to understand how the brain controls those behaviors. This now allows us to easily home in on the neurons that are causing those differences.”
Gerry Rubin, head of biology and a senior group leader of the Howard Hughes Medical Institute’s Janelia Research Campus, via Livescience
Mapping Taste Circuits and Sensory Processing
One of these studies, led by researchers at the Champalimaud Foundation in Lisbon, focused specifically on how fruit flies process and react to tastes.
Fruit flies possess taste receptors distributed across multiple body parts, including their legs, wings, mouthparts, and inside of the throat. Scientists traced these sensory inputs directly into the brain to observe how taste pathways intersect with motor circuits that control swallowing and walking. This circuitry enables the insect to evaluate whether a potential food source is safe or harmful before deciding to eat.
“Suppose you are interested in how taste controls locomotion. Now you can go to the map and ask: which sensory neurons are connected to the neurons controlling locomotion? Which intermediate neurons should I manipulate? It gives you a place to start.”
Inês de Haan Vicente, a research technician in Ribeiro’s lab, via Livescience
Broader Implications for Artificial Intelligence and Future Connectomics
Beyond entomology, researchers emphasize that understanding the fly nervous system could have practical technological payoffs. Carlos Ribeiro, a principal investigator at the Champalimaud Foundation whose team contributed to the mapping project, noted that the fly achieves remarkable computational feats while consuming minimal energy.
“The fly nervous system performs remarkably sophisticated computations with relatively few neurons and little energy, and its architecture could suggest principles for designing more efficient artificial systems.”
Carlos Ribeiro, principal investigator at the Champalimaud Foundation, via Livescience
Scientists view the male fruit fly connectome as a vital stepping stone toward far more ambitious mapping initiatives. Researchers eventually aim to map the brains of larval zebrafish and adult danionin fish, with the ultimate long-term goal of illuminating vertebrate brain function and unraveling the roots of human neurological and psychiatric disorders.
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