# We ran a fruit fly's whole brain on a laptop and gave it sugar. What did it do?

- Series: [How Computers Work](https://miu.fm/howcomputerswork.md)
- Published: 2026-10-24
- Page: https://miu.fm/howcomputerswork/we-ran-a-fruit-fly-s-whole-brain-on-a-laptop-and-gave-it

## Story

We ran a fruit fly's whole brain on a laptop and gave it sugar. What did it do?

The map is FlyWire (Nature, 2024): 139,255 neurons and 54.5 million synapses between them, traced from about 21 million microscope images. Those images fill about 106 TB. The wiring itself is a list of who connects to whom and how strongly: 15,091,983 pairs of neurons, about 151 MB written out plainly, small enough for a laptop's memory.

To run it we wrote our own copy of the model Philip Shiu and colleagues published in Nature in 2024: every neuron adds up what reaches it through its connections and fires when the total passes a threshold (their published values: -52 mV rest, -45 mV threshold, 0.275 mV per synapse). We switched on the 20 sugar-tasting neurons. About 360 neurons fired. Three strong links away (5 or more synapses each) sits MN9, a motor neuron that lifts the fly's mouthparts to feed. It fired in all 30 of our runs, about 71 times a second.

Then the control: we kept every connection and its strength but sent each one to a random neuron, a new random wiring for each of 30 runs. MN9 stayed silent in all 30. Same neurons, same numbers; the difference was the wiring. One second of the fly's brain took the laptop about 16 seconds to run (the mean of 30 runs, measured on a laptop, 2026).

What it isn't: a fly. It's a model of the brain alone, from its wiring and predicted transmitters, with no body, no hormones and no gap junctions; its makers write that its firing rates "are unlikely to be accurate". The brain in the film is our own drawing; the dots are not the neurons' real places.

What would you test on a fly brain?

Sources: Dorkenwald et al., Nature 634, 124 (2024); Schlegel et al., Nature 634, 139 (2024); Shiu et al., Nature 634, 210 (2024); Zheng et al., Cell 174, 730 (2018). Data: FlyWire Consortium, FlyWire connectome v783 (synapses Buhmann et al. 2021 and Heinrich et al. 2018, transmitters Eckstein, Bates et al. 2024), as prepared in Shiu et al.'s model files (MIT), licence CC BY-NC 4.0 (creativecommons.org/licenses/by-nc/4.0). The counts, chain and runs are our own analysis of the data.
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