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The Latest Weird Thing to Play Doom Is the Mapped-Out Brain of a Fruit Fly

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Why This Matters

A software engineer used Google and HHMI Janelia's record-breaking fruit fly connectome — 166,000 neurons across 11,700 types — to build a simulated brain that plays Doom frame by frame. It's a playful stunt, but it shows how openly published neuroscience data can be repurposed as a functional computational substrate, and it keeps the 'it runs Doom' tradition alive as an informal benchmark for novel computing platforms.

Key Takeaways
Worth a Look

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Doom is such a simple, beautifully designed game that it can run on all sorts of weird things, from pregnancy tests to potatoes. Weird things can play it, too. In an effort to eternally one-up itself, the community has now gotten a map of a fruit fly’s brain to play the 1993 first-person shooter.

It started with Google, which partnered with HHMI Janelia Research and other collaborators to map the brain and central nervous system of a male fruit fly. This mapping, which is weirdly beautiful, contains 11,700 types of neurons and 166,000 neurons overall, breaking the record for the most complex neuron mapping ever done.

The research is pretty cool: It involved taking very thin slices of a fly’s brain and body, imaging them and using AI to combine the millions of 2D images into 3D neural shapes. Google says that “knowing the structure of the brain allows neuroscientists to understand the mechanisms behind brain function.”

Now, make it play Doom

The game is played frame by frame, letting the fly’s simulated brain determine its next move based on what it sees. Doomfly

It turns out that knowing the structure of the male fruit fly brain can also help modders and developers teach it how to play Doom. A few days after Google dropped its fly brain research, software engineer Alex Wormuth created a simulated fly brain using Google’s map and then set it loose to learn how to play the pioneering FPS.

The process is quite complicated. Each frame of the game generates 3,335 brightness inputs and 811 R8 color inputs. These inputs are fed into the simulated fruit fly brain, which contains 25.6 million connections. These inputs hit specific neurons based on what the frame shows, and that information is used to determine which controls the fly uses. This process repeats each frame the game runs.

It even works with pain. Wormuth says that nonfatal damage targets the PPL101 dopamine receptors, which control hunger and aggression in real fruit flies.

You can watch the fly’s progress in learning how to play Doom on Wormuth’s Doomfly website, which also shows sensory input, neural activity and other metrics so you can watch the simulated fly brain work in real time. If you swap to the 3D view, you can watch the fly shoot demons.

Flying high with other games, too

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