Fly connectome demos aren't what they seem: Beat Saber video is overfit replay, real RL not done yet
dotey · x · 2026-09-10
dotey debunks the viral "fly brain playing Beat Saber" video: the motion output is a model overfit to pre-recorded sequences and replayed—no real vision or RL yet, and the connectome is a static wiring diagram.
Key facts:
- On Sep 3, HHMI Janelia, Google Research, and Cambridge published the complete male fly CNS connectome in Cell: 166,700 neurons and 125M synapses, the largest full brain map, covering brain plus ventral nerve cord, CC-BY open-sourced.
- Two days after release, Georgia Tech grad student Evan Smith fit all neurons into Minecraft using GPT-6 Astra; Beat Saber, Mario 64, and Doom demos followed.
- Real finding: comparing male vs female connectomes at synapse precision, only 4.8% of neurons show sex differences, concentrated in decision-making regions—sensory/motor areas are nearly identical.
- Next: Google and Harvard mapping the zebrafish whole-brain connectome; mouse regions in progress.
Related event: Viral 'Fly Brain Plays Beat Saber' Turns Out to Be Overfit Replay(3 posts)→
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