Fruit Fly

A whole fruit fly nervous system, alive in a world.

The complete adult male Drosophila central nervous system, MaleCNS v1.0, runs here as a spiking network on the graphics card: 164,587 neurons and 25,563,197 connections, the real wiring, stepping in real time. It is wearing a fly. What that fly tastes, sees and does all passes through the network, and you can reach into the network while it happens.

Your first minute

You arrive in the lab looking at the brain on its plinth. The fly is on the floor in front of you. A card in the top right walks you through the first experiment in four steps, and ticks each one as you do it. It takes about a minute and it ends with a proboscis coming out of a fly because a signal crossed a real connectome to get there.

What is on screen

The bench, on the left. The network's state along the top, three knobs under it, and then everything you do: a selection line where you name a set of neurons, and stimulate, silence, restore, watch and count. Under that are the readings: every group you are watching with its rate and a bar, a trace of the last 24 seconds, the hottest cell classes, who is driving what, the neuron you last clicked on, what the fly's body is doing, and a colour legend for the cloud.

The experiments panel, on the right, opened with the Experiments button or the P key. Five protocols from the guide, each one press. A protocol clears the drives, resets every membrane, records a baseline, applies its own stimulus and ablations, samples every readout, puts the parameters back and prints a verdict in the dataset's own terms. COMPARE lays the previous run's trace over this one.

The world. A 12 metre arena. Three food discs. The fly, which walks, turns, feeds, beats its wings and jumps, and which cannot leave the arena because it sees the wall the way it sees anything else coming at it.

Naming neurons

A selection is space-separated key:value terms. The chips above the selection line fill in the common ones.

term	selects
type:MN9	an exact cell type, or several separated by commas
prefix:JO-	every type whose name starts so
pattern:^LB%d	types matching a pattern
class:Kenyon_Cell	a class
super:descending_neuron	a superclass
side:L	one side
excitatory:true	only the excitatory neurons
limit:100	at most so many

Press count to see how many neurons match before you do anything to them.

The five experiments

1. Taste to the proboscis. Drive the fly's 50 tarsal taste pegs and its two proboscis motor neurons answer within a few hundred milliseconds, while the mushroom body stays quiet.
2. Gain recovery. Sweep the gain: at 0.5 the signal reaches nothing, at 0.6 it reaches the proboscis and nowhere else, at 1.0 it runs away.
3. Looming and escape. Walk at the fly. Its looming detectors fire, the giant fibre bursts and it jumps. Silence one detector class and walk at it again.
4. Ablation. Silence the Kenyon cells, or the descending neurons, or one side of a turn neuron, and watch what the fly stops being able to do.
5. Two brains, one arena. Put a second connectome in a second fly.

The experiments guide, inside the package, is the long version.

Controls

Every action is reachable with a mouse and keyboard, with a touchscreen, and with a controller.

	mouse and keyboard	controller	touch
walk, look	WASD, mouse	left stick, right stick	left stick zone, right drag zone
jump	Space	A	Jump button
open the bench	L, or the Lab button	Start	Lab button
move through the bench	arrow keys or Tab	D-pad	tap the control
use the focused control	Enter	Y	tap it
nudge a slider	left and right arrows	D-pad left and right	drag it
identify a neuron	click the cloud	X	ID button
open the experiments	P	Select	Experiments button
next protocol	N	right stick press	tap it
previous protocol	B		tap it
run, compare	R, C	right trigger, left trigger	tap them

Sound

The fly's wingbeat follows its flight muscles, a wet tick marks a meal and a thump marks a jump. The brain crackles in proportion to how much of it is firing: a quiet network is a quiet room.

The science

Every cell type, class, superclass and side named anywhere in this world is what MaleCNS v1.0 calls it. Every constant in the network is from the published model. Nothing here is invented biology, and where a number is the world's own choice rather than the dataset's, it says so.

The dataset is CC-BY 4.0, Berg et al. 2026, Cell.

spec.md beside this file is the design of record, and the fruitFly package carries its own README and the experiments guide.