After nearly two decades of work, scientists have completed a wiring diagram of the central nervous system of an adult male fruit fly (Drosophila melanogaster).
The wiring diagram of the central nervous system of an adult male fruit fly will help researchers better understand how the brain enables complex action, from sensory perception to behavior. Image credit: FlyEM Project Team, HHMI’s Janelia Research Campus / Cambridge Connectomics Group / Google Research / Philip Hubbard, HHMI Janelia Research Campus.
“We felt, which wasn’t a universally accepted idea, that we wouldn’t be able to understand the brain at a satisfying level without having a wiring diagram,” said Dr. Gerry Rubin, founding executive director of the Howard Hughes Medical Institute’s Janelia Research Campus.
“We knew it was possible; it was a well-defined problem. We just had to figure out how to do it.”
The newly completed connectome is the first map of an entire male fruit fly central nervous system.
The map charts 166,700 neurons that make up the fly’s brain and ventral nerve cord, along with the millions of connections between them.
It is the first connectome ever assembled for a complete central nervous system of this complexity, following a partial map — the ‘hemibrain,’ covering roughly half the fly’s brain — that the same team released in 2020.
“There’s a point where people lack imagination, but they finally see something and say, ‘I got it.’ This is why this is going to be really important,” Dr. Rubin said.
“That’s what the hemibrain did for neuroscientists by showing what you could learn from a connectome.”
“It just changed the attitude of people about what was going to be possible.”
The new map will allow scientists to trace the complete neuronal circuits that link sensory perception to behavior, enabling researchers to determine how flies carry out key actions, like navigating to a goal.
It will also allow researchers to compare male and female brains and understand complex social behaviors — like mating and aggression — that can vary by sex.
“For me, I’ve been doing this for a long time, longer than I’ve ever worked on any other scientific goal in my life and I’m ready to stop and think about something else,” Dr. Rubin said.
“But with an immense sense of pride and accomplishment for the group of people that we brought together here and that pulled it off.”
A paper describing the results appears in the journal Cell.
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Stuart Berg et al. Sexual dimorphism in the complete Drosophila male central nervous system connectome. Cell, published online September 3, 2026; doi: 10.1016/j.cell.2026.08.015
