Google and Partners Map Complete Male Fruit Fly Brain

Google Research, in partnership with the Howard Hughes Medical Institute (HHMI) Janelia Research Campus, has published the largest brain map to date, detailing the complete brain and central nervous system of a male fruit fly. Published in the journal Cell, the project charts more than 166,000 neurons and 125 million synaptic connections. This connectome includes the ventral nerve cord, which functions similarly to a spinal cord, allowing researchers to study how the brain coordinates physical movement.

To construct this cellular-scale map, researchers used advanced machine learning techniques to stitch together millions of thin electron microscope images. Google utilized flood-filling networks, which employ convolutional neural networks to trace neural pathways pixel by pixel. They also used PATHFINDER, a reconstruction system trained on synthetic neurons to accelerate the process. This automated reconstruction builds on previous milestones, including a 2019 automated female brain map and a 2020 human-verified map of half a female brain containing 25,000 neurons and 21 million connections.

For neuroscience practitioners, this dataset—accessible via Googles open-source visualization tool Neuroglancer—enables direct comparison with existing female fruit fly connectomes. Researchers can now analyze structural differences, such as the dimorphic AOTU008 pathway, to study the biological basis of courtship, aggression, and individual variability. Additionally, the methods developed here are scaling to vertebrates. Google has collaborated with Columbia University to map the hindbrain of the elephantnose fish and is working with Harvard on a whole-brain dataset for larval zebrafish, utilizing the ZAPBench and Fish Fire&Wire datasets to combine neural structure with electrical activity.