Google Research and the Howard Hughes Medical Institute's Janelia Research Campus have published the first complete wiring diagram of a male fruit fly's brain and central nervous system — the largest connectome mapped to date. The map covers more than 166,000 neurons and 125 million synaptic connections, spanning the brain, both optic lobes, and the ventral nerve cord.
The team built the connectome by slicing a fly brain into millions of ultra-thin sections, imaging each one with electron microscopy, then using AI reconstruction tools — including flood-filling networks and Google's PATHFINDER system — to stitch the images into a 3D map, before human experts verified and annotated the resulting structures. The findings were published in the journal Cell.
The male map complements a female fruit fly connectome released earlier this year, letting researchers directly compare neural circuits tied to sex-specific behaviors such as courtship and aggression. The dataset is freely explorable through the open-source Neuroglancer tool, and the team says the techniques developed here are already being applied to map larger brains, including those of zebrafish and mice.