fruitFly

A whole fruit fly nervous system running as a spiking network on the GPU, a fly body it drives, and a bench for experiments on it. Install this package and a world holds the complete adult male Drosophila central nervous system (MaleCNS v1.0: 164,587 neurons, 25.6 million connections, CC-BY 4.0) as a leaky integrate-and-fire network you can stimulate, silence, read out and watch, plus a fly whose taste, looming, walking, turning, feeding, flight and escape run through that wiring.

Contents

The network:

• maleCNS.connectome/ is MaleCNS v1.0 packed for the GPU (109 MB, the edge table in two parts). It is an instance of the connectome asset type, which lives at the world root (/zero/source/connectome.assetType/) and travels with the package as a dependency: any nervous system's wiring as one asset (manifest.json, neurons.bin, offsets.bin, edges.bin or its parts). guides { path = "types/connectome" } is the reference.
• lif_integrate, lif_propagate, lif_clear, lif_reset (.computeShader) are the four kernels of the network: membrane step, event-driven spike propagation over the CSR edge table, step close, reset.
• brain.module/ is Brain.load(connectomeRef, params), which binds a connectome to the kernels and returns the network: step, update, select, stimulate, silence, watch, rates, activity, classRates, groupActivity, drives and the cloud.
• FruitFlyBrain.component/ puts a network on an entity: it loads the connectome the connectome field names, steps it every frame, draws the cloud, and exposes stimulate / silence / watch / rates / reset (the first three are synced, so every peer's copy receives the same inputs).
• neuron.shader/, neuron.material/ and cloud_gather.computeShader/ are the instanced neuron cloud, each neuron lit by its own activity.
• crackle.soundClip/ is the network's own sound: a sparse crackle that is silent when the network is silent and a hiss when it runs away.

The fly:

• flyBody.module/ is the fly's body as an entity tree with a tripod gait, wings, proboscis and a hop.
• FruitFly.component/ is the embodied fly: it reads the world into the brain's sensory neurons and reads motor commands back out of named cell types.
• FoodPatch.component/ is a disc of food on the ground the fly can taste.
• wing.material/, eye.material/ and the wingbeat, feed and jump sound clips are what the fly looks and sounds like.

The instrument:

• FruitFlyLab.component/ is the bench window: network state and knobs, live readouts with traces and rasters, hot classes, live drives, a neuron panel, a legend, and a selection line to stimulate, silence, restore, count or watch any set of neurons.
• selection.module/ is the selection grammar the bench and everything else parse with.
• protocol.module/ is the guide's experiments as records anything can run, and the verdict a run computes from its own numbers.
• FruitFlyExperiments.component/ is the experiments panel: those protocols with one press each, a run list, a compare overlay and a verdict line.
• FirstRun.component/ is the four-step card that walks a newcomer from a reset network to a proboscis coming out.
• lab.inputMap/ and experiments.inputMap/ are the bench's and the panel's controls, each binding keyboard, gamepad and touch.
• experiments.guide/ is the bench manual and the five experiments.

The lab around it:

• labFloor.material/ and FruitFlyLook.component/ are the floor, the fog, the vignette and the lighting intent, held as data rather than as code.
• arenaRing.mesh/ is the ring on the floor the fly stays inside.

Usage

-- The brain: one entity, one network. The default connectome is maleCNS.
local brainEnt = entity.spawn("Brain")
brainEnt.position = { 0, 6, -8 }
brainEnt.component.add("FruitFlyBrain", { gain = 0.6, timeScale = 1 })

-- An embodied fly driven by it, and something for it to taste.
local fly = entity.spawn("Fly")
fly.component.add("FruitFly", { brain = brainEnt, bodyLength = 0.6 })
local food = entity.spawn("Food")
food.position = { 3, 0, 0 }
food.component.add("FoodPatch", { radius = 0.6, sugar = 1 })

-- The bench, the experiments panel and the card.
entity.spawn("Lab").component.add("FruitFlyLab", { brain = brainEnt, fly = fly })
entity.spawn("Experiments").component.add("FruitFlyExperiments", { brain = brainEnt, fly = fly })
entity.spawn("FirstRun").component.add("FirstRun", { brain = brainEnt, fly = fly })

-- Or from code:
local comp = brainEnt.component.get("FruitFlyBrain")
comp:watch("MN9", { types = { "MN9" } })                 -- proboscis motor neurons
comp:stimulate({ types = { "claw_tpGRN" } }, 100)        -- tarsal taste pegs at 100 Hz
print(comp:rates().MN9)                                   -- Hz per neuron, updated every frame

A selection names neurons by the dataset's own vocabulary: types (exact cell-type names), typePrefix, pattern (a Lua pattern over the type name), classes, superclasses, sides (L/R/M), excitatory, indices, limit. brain:info(i) answers what any neuron is.

The model

Every neuron is a leaky integrate-and-fire unit with the constants Shiu et al. 2024 (Nature) fitted to the FlyWire brain: rest and reset at -52 mV, threshold -45 mV, membrane time constant 20 ms, synaptic time constant 5 ms, refractory period 2.2 ms, transmission delay 1.8 ms, 0.275 mV per synapse. A presynaptic neuron whose consensus transmitter is GABA, glutamate or histamine inhibits; every other transmitter excites. A connection carries its synapse count; connections under minSynapses (default 5) carry nothing.

gain scales every synapse. MaleCNS traces about 2.5 times the synapses per connection FlyWire does, so at gain 1 the network runs away under any drive; at 0.6 (the default) driving the 50 tarsal taste-peg neurons at 100 Hz holds the proboscis motor neurons MN9 at about 115 Hz while the Kenyon cells stay under 0.1 Hz, and driving the 595 Johnston's organ neurons instead leaves MN9 at zero. At 0.5 the taste drive reaches nothing. The bench's gain slider is the experiment, and the experiments panel's "Gain recovery" runs all three in one press.

Everything runs on the GPU: the state, the input ring, the spike list and the edge table. The CPU sees the per-group spike counters each frame and, on request, the per-neuron activity lane. Integer atomics make a step order-independent, so two peers stepping the same inputs read the same network.

The fly

FruitFly reads named cell types out of the brain and writes the world into others; every name is in FruitFly.component/init.luau:

The two looming paths are driven separately and weighted by how head-on the approach is, so an avatar walking up behind the fly does not loom and silencing one detector class is an experiment with an answer.

The body moves kinematically at walkSpeed body lengths per second; the fly faces its entity's -Z. On a shared world the entity's owner writes the senses into the brain (a synced call) and every peer poses its own copy from its own network.

Controls

Both maps name their controls apart (lab* and exp*) and take disjoint keys and buttons, so the bench and the panel can be open together and neither answers for the other.

Data and license

MaleCNS v1.0: HHMI Janelia FlyEM, Google Research and the Cambridge connectomics group, released 8 June 2026 (Berg et al. 2026, Cell, doi:10.1016/j.cell.2026.08.015), CC-BY 4.0. The pack was written by a script that reads the public flat-connectome export (connectome-weights ... traced-only, body annotations, consensus neurotransmitters), assigns dense indices, sorts edges by presynaptic neuron and writes the four files types/connectome describes; the manifest carries each source file's SHA-256.

Notes

• Loading the network reads the 102 MB edge table into a GPU buffer once per FruitFlyBrain; the VFS copy is released afterwards.
• The neuron cloud is one instanced draw of every neuron with a soma (139,741). Its transforms are static; the activity lanes are written by the integrate kernel.
• maxStepsPerFrame bounds GPU time per frame; at 32 steps of 1 ms a 60 fps engine keeps up with real time.
• A neuron reads out under at most three groups at once. The fly holds seven of its own and the protocols watch five more under the guide's names, so a bench watch of the same cell types under the same name shares the group rather than spending another slot.