FlyWire consortium publishes the first complete connectome of an adult fruit fly brain

Filed retrospectively. Before the Specola kept its nightly watch, these were the observations that turned the telescope.

On October 2, 2024, the journal Nature published a nine-paper package describing the first complete connectome of an adult fruit fly brain, the largest and most complete wiring diagram of a whole animal brain produced to that date. The map details 139,255 neurons and more than 50 million synaptic connections, and classifies over 8,400 cell types. The work was produced by the FlyWire Consortium, a collaboration of dozens of laboratories across many institutions, with partial funding from the U.S. National Institutes of Health.

The effort was led from the Princeton Neuroscience Institute by neuroscientist Mala Murthy and computational neuroscientist Sebastian Seung, working with the MRC Laboratory of Molecular Biology in Cambridge, the University of Cambridge, and the University of Vermont, among others. The team reconstructed the connectome from electron-microscope images of a single fly brain, using machine learning to trace neurons and to predict which neurotransmitters their connections use, then correcting the result through extensive human proofreading.

Seung framed the significance broadly, saying that “any brain that we truly understand tells us something about all brains.” Earlier complete connectomes covered far simpler systems, the roundworm C. elegans with 302 neurons and the fruit fly larva with about 3,000. The adult fly map became the reference substrate for later work that placed the connectome inside simulated bodies.