Scientists have mapped every single neuron in the adult male fruit fly central nervous system, recording more than 166,000 neurons. Published on Thursday (Sept. 3), the complete connectome enables direct comparisons with a female fruit fly brain map released in 2024, opening new doors for understanding sex-specific behaviors like mating and aggression.
A fruit fly brain fits roughly inside the volume of a poppy seed, yet that micro-scale package houses a staggering density of neural wiring. In a landmark mapping effort, researchers have charted every single neuron in the male fruit fly, including both optic lobes and the ventral nerve cord.
Charting 166,000 Neurons Across the Male Fruit Fly Nervous System
The project represents years of collaborative work spanning the Howard Hughes Medical Institute’s Janelia Research Campus, Google Research, and international scientific partners. AI played a pivotal role by allowing researchers to scale the painstaking reconstruction of brain cell connections. This male connectome builds directly upon the completion of a female fruit fly brain map released in 2024, which charted roughly 140,000 neurons across the female central nervous system.
Having complete wiring diagrams for both sexes provides a unique comparative window that was previously impossible to open in animals with intricate social repertoires. Male and female flies have a lot of differences in their behavior, making the dual maps essential instruments for isolating the exact neural pathways driving those distinctions.
“It is the first time we can compare both sexes of an animal with complex social behavior,” study co-author Gerry Rubin, head of biology and a senior group leader of the Howard Hughes Medical Institute’s Janelia Research Campus, said in a statement. “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, study co-author, head of biology and a senior group leader of the Howard Hughes Medical Institute’s Janelia Research Campus
Unlocking the Circuitry Behind Taste, Mating, and Aggression
The male connectome was unveiled alongside three companion papers in the journals Cell and Current Biology Thursday (Sept. 3). Each study leverages the new neural map to investigate distinct domains of insect neurobiology, ranging from vision processing to sex-specific behavioral divergences.
One prominent study, led by scientists at the Champalimaud Foundation in Lisbon, zeroed in on the insect’s sense of taste. Fruit flies possess taste receptors distributed across their legs, wings, mouthparts, and throat. Researchers traced these peripheral sensors directly back to the central brain to observe how taste circuits interface with networks controlling locomotion and swallowing.
This neural tracking reveals how an individual fly evaluates whether a potential food source is safe or harmful before executing a feeding decision.
“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, research technician in Ribeiro’s lab at the Champalimaud Foundation
Building a Technical Roadmap for Mouse and Human Connectomics
Beyond immediate behavioral insights, researchers view the fruit fly connectome as a proof-of-concept for far larger neuroscientific endeavors. Because AI is making it possible for scientists and researchers to exponentially scale projects in connectomics, the methods honed on insect brains are already pointing toward mammalian applications.
The fly nervous system performs remarkably sophisticated computations with relatively few neurons and little energy
, noted Carlos Ribeiro, a principal investigator at the Champalimaud Foundation whose team contributed to the mapping effort. Ribeiro added that the architecture uncovered by the project could suggest principles for designing more efficient artificial systems
while laying down a technical framework for mapping vertebrate brains.
In the near term, teams aim to target the nervous systems of larval zebrafish and adult danionin fish. Over a longer horizon, researchers intend to use these simpler model organisms to understand how vertebrate brains coordinate complex behaviors—ultimately helping science unravel the neurological and psychiatric conditions that affect humans.