// 138,639 NEURONS — 15,091,983 CONNECTIONS — ONE FLY
FLY BRAIN
Every neuron in a fruit fly's brain and every connection between them, as FlyWire mapped them, firing in your browser. Paint the brain to stimulate it, give the fly something to taste or a shadow to fear, play it some bass, and watch what the wiring alone does with it. Nothing here was trained.
> HOLD A SENSE ON: ITS NEURONS FIRE AT THE RATE BELOW, LIKE OPTOGENETICS
> PUT SOMETHING IN FRONT OF IT (OR PICK ONE, THEN TAP THE FLOOR)
> SOMETHING SWOOPS IN
Taste reaches the brain when the fly's head is in a drop. The fly walks because its P9 walking neurons are driven (MODEL); everything else it does, it does because something fired.
> WHAT THE ANTENNAE HEAR
Louder in a band, faster its Johnston's organ neurons fire, up to 220 Hz. Loud enough and the giant fiber fires, and the fly bolts. The track is made here in Web Audio; the microphone and your file stay in the page.
Loading the map of the brain (about 1 MB)…
How it works
01 / THE WIRING FlyWire traced every neuron in one adult female fly's brain from electron micrographs: 138,639 neurons and 54,492,922 synapses, 15,091,983 connections between pairs of cells. Each connection is excitatory or inhibitory by the transmitter its sender is predicted to release. None of it is pruned here; it is a 31 MB download.
02 / THE NEURONS Philip Shiu and colleagues made every neuron the same leaky integrate-and-fire cell and let the wiring decide the rest. Their model predicted which neurons drive feeding and grooming, and experiments agreed nine times in ten. This page runs it in JavaScript, step by tenth of a millisecond, and matches their Brian2 simulator neuron for neuron (r = 0.9998).
03 / THE BODY The brain has no legs: the data stops at the neck. So the fly is a puppet that reads 56 of the neurons that leave the brain, P9 to walk, MDN to back up, DNa01 and DNa02 to steer, MN9 for the proboscis, DNg12 to groom and the giant fiber to escape, and turns their firing into motion by fixed rules.
The model is Shiu et al.'s
(Nature, 2024;
MIT), on the
FlyWire connectome (Dorkenwald et al. 2024, Schlegel et al. 2024; CC-BY 4.0),
version 783, from 91bdd1e. The brakes and the event-driven trick that makes it fast enough come
from stonkfly, which hands a fly brain a trading account; the
idea of a body for it from Eon Systems, who run the same
model on GPUs and neuromorphic chips. The fly and its arena are this site's. Nothing you do leaves the page.