# 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 - `maleCNS.connectome/` — 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`) — the four kernels of the network: membrane step, event-driven spike propagation over the CSR edge table, step close, reset. - `brain.module/` — `Brain.load(connectomeRef, params)` binds a connectome to the kernels and returns the network: `step`, `update`, `select`, `stimulate`, `silence`, `watch`, `rates`, `activity`, `showCloud`. - `neuron.shader/` + `neuron.material/` — the instanced neuron cloud, each neuron lit by its own activity. - `FruitFlyBrain.component/` — puts a network on an entity: 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). - `flyBody.module/` — the fly's body as an entity tree with a tripod gait, wings, proboscis and a hop. - `FruitFly.component/` — the embodied fly: reads the world into the brain's sensory neurons and reads motor commands back out of named cell types. - `FoodPatch.component/` — a disc of food on the ground the fly can taste. - `FruitFlyLab.component/` — the bench window: network state and knobs, live readouts with traces, and a selection line to stimulate, silence, restore or watch any set of neurons. - `experiments.guide/` — the experiments the bench was built for, and how to run them. ## Usage ```luau -- 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. entity.spawn("Lab").component.add("FruitFlyLab", { 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 fires the proboscis motor neurons MN9 at about 120 Hz while the Kenyon cells stay under 0.1 Hz, and driving the 595 Johnston's organ neurons instead leaves MN9 silent. At 0.5 the taste drive reaches nothing. The bench's gain slider is the experiment. 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`: | command | cell types | |---|---| | walk | the leg motor neurons (`vnc_motor` types ending in ` MN`) | | turn | `DNa01`, `DNa02` left minus right | | proboscis | `MN9` | | flight | the wing power-muscle motor neurons (`DLMn`, `DVMn`) | | jump | a `DNp01` (giant fibre) burst | | sense | cell types | driven by | |---|---|---| | tarsal taste | `claw_tpGRN`, `dorsal_tpGRN` | a front foot on a `FoodPatch` | | labellar taste | `LB*` labellar bristle GRNs | the extended proboscis on a `FoodPatch` | | looming | `LPLC2`, `LC4` | any player's avatar growing fast in the fly's view | 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. ## 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.

# lif_integrate The membrane step of the `brain` module's leaky integrate-and-fire network, one thread per neuron. It drains this step's slot of the fixed-point input ring into the neuron's synaptic conductance, advances the membrane by exponential Euler on `dv/dt = (vRest - v + g) / tauM` and `dg/dt = -g / tauSyn`, holds a refractory neuron at reset, draws the neuron's external Poisson event from its `stim` rate, and on a spike resets it, appends its index to this step's spike list, and bumps the total and its readout group's counter. Every neuron writes its activity trace, normalised membrane and spike flag into lane 0 of the visualisation buffer the neuron cloud draws from. `decayMem` and `decaySyn` are `exp(-dt / tau)` computed once by the module; the step index comes from the GPU clock so several steps can be queued in one frame with no CPU write between them.

# lif_propagate The synaptic step of the `brain` module's network. Each workgroup takes one spike from this step's list, and its 64 threads stride that neuron's outgoing edge row, adding every connection's synapse count times `unitsPerSynapse` (signed by the presynaptic neuron's transmitter) into the fixed-point input ring at the slot `delaySteps` after the current step. A connection carrying fewer than `minSynapses` synapses is skipped, which is how the module applies the connection threshold whole-brain models are fitted with (five, in Shiu et al. 2024) without repacking the table. The module dispatches it with `maxSpikes` workgroups; a workgroup past this step's spike count returns at once. The sum is integer atomics, so the result is the same whatever order the threads land in.

# lif_reset Puts the `brain` module's network at rest in one dispatch: every membrane at `vRest` with no synaptic conductance, refractory time or activity trace, every slot of the input ring empty, the visualisation lane dark, the spike list empty, every spike counter zero and the step clock at zero. The module runs it once after allocating a network and again on `brain:reset()`.

# lif_clear Closes one step of the `brain` module's network: empties the spike list the integrate kernel filled and the propagate kernel consumed, and advances the GPU step clock by one. The clock living on the GPU is what lets the module queue several steps in one frame, each reading its own ring slot, with no CPU write between dispatches.

# neuron The surface of one neuron in the brain's instanced neuron cloud. It lights itself from the instance data the brain's integrate kernel writes each step (lane 0: activity trace, normalised membrane, spike flag) and the class colour the module writes once (lane 1): dim at rest, brighter as the membrane depolarises, flaring to full emission on a spike and fading with the trace. `rest_brightness`, `membrane_brightness` and `spike_brightness` set those three levels on the material.