# Can a Fruit Fly Brain Learn Numbers?

> Source: <https://julin.ai/2026/09/11/fly-circuit-on-mnist/>
> Published: 2026-09-10 12:00:00+00:00

Following up on [A Fruit Fly Circuit as a Speech Emotion Reservoir](https://julin.ai/2026/09/09/fly-brain-emotion/): I pulled the real 499-neuron circuit out of MaleCNS v1.0 and ran it as a reservoir on MNIST, in PyTorch and in [MLX](https://github.com/ml-explore/mlx). Code and data: [gist](https://gist.github.com/soasme/caa8b071e85d76aff44aec8f259d0870).

[MaleCNS v1.0](https://male-cns.janelia.org/download/) is a public, CC-BY electron-microscopy reconstruction of a male fruit fly’s central nervous system.

I applied the selection rule stated in the original article: central-brain intrinsic neurons, traced status, ranked by strength, top 512, largest strongly connected component, edges with at least 5 synaptic contacts. This landed on exactly 499 neurons — the same count the paper reports — with 13,452 directed edges, against their reported 15,865. Their exact ranking formula for “strongest” isn’t published, so this is the closest match I could reproduce.