Is the fruit fly brain simulation real? What is measured, modelled, hand-made or scripted

New test: is the fly brain really playing Doom?

Added 28 Sep 2026, chart of all 18 results added 1 Oct 2026 · third-party numbers, not reproduced by us

DOOMFLY is the viral "fly brain plays Doom" demo. A third-party study by gabrycina, doom-fly-control (grade A; code), ran DOOMFLY's own code again with its eyes, brain and button mapping unchanged, and compared it with controls. One of them is a brainless autopilot: it always turns a little, walks forward and holds the trigger, at constant rates.

Two other Doom projects with controls point the same way. In doomfly-rl (grade A), a network wired like part of the fly brain is trained to play; real, shuffled and no wiring score the same, both in the author's tests and in doom-fly-control's 100-game re-run. In flydoom by mutkuoz (grade A), an untrained FlyWire whole-brain model beats a random agent with matched commands only narrowly, in one purpose-built arena, and mirroring its eyes removes that advantage. Its author's commits of 29 Sep re-score a separate "everything applied" variant, whose extra health turned out to come from the arena; the plain model's vision control and its grade A stand.

Our verdict on DOOMFLY stays at B: a real connectome runs and drives the game, with hand-made input and output, and there is no evidence of skilled play. More on the DOOMFLY project page.

The counterpoint: a closed loop where the real wiring matters

Added 29 Sep 2026 · the authors' numbers, means recomputed by us from their per-fly table, not re-run

A new study, "Are fruit flies zero-shot adapters?" (grade A), connects three published parts: the FlyVis eye model, the Shiu et al. whole-brain model on FlyWire v783 with unchanged weights, and a NeuroMechFly body. The fly walks toward dark poles; two of its legs are removed mid-walk, and it keeps finding them. The same flies are then run with scrambled wiring and with the turn neurons disconnected.

Set next to the Doom test, the two studies ask the same question and get opposite answers. Both include a baseline in which the brain does not steer (dashed bars): in Doom, a constant command plays as well as the brain; here, a fly that walks without brain steering almost never reaches a pole.

This is the kind of test the viral game demos lack. It still does not show skilled behaviour beyond steering toward a dark object, a classic fly reflex. Full details in the catalogue entry and in its row on Does fly wiring help?

We ran the map: is it a brain or just a map?

Added 5 Oct 2026 · made by us · pre-registered at 09:42:47 UTC before the first trial · it changes no grade

We ran the map. A looming shadow on one eye turned our simulated fly away in 4 of 4 runs. With the same map scrambled (same number of connections per neuron) it turned away in 0 of 3. Here the map's wiring, not the stimulus or our code, makes the turn.

"It's just a map" is the most common reply to the viral fly videos, and it is half right: the connectome is a wiring map of one fly, not a living brain. So we asked what the map does when it runs. FLY67, a browser fly, claims that a looming shadow on one eye makes its fly turn away: the eye's looming detectors (LC4 and LPLC2) excite the escape neuron (the giant fibre) and the turning neurons DNa02 on the far side. We rebuilt that test with the Shiu et al. whole-brain model on FlyWire v783, showed the shadow to one eye, and let the brain's turning neurons steer a simulated FlyGym fly through a rule we wrote by hand, on top of a constant walking drive that is also ours. Then we did the same with scrambled maps that keep every neuron's number of connections, with no brain at all, and with random steering.

What the brain sends down, beside fly67's own numbers

fly67's own pass rule held in our Brian2 run, so the brain part is reproduced in a second engine: giant fibre 111.5–120.5 Hz (fly67's engine: 114.8 and 120.3 Hz), DNa02 on the far side 23–44 Hz, on the near side 0 Hz. In every scrambled map all of these stayed at 0 Hz. fly67 stays grade B: our test is not the author's own control.

Share it with its caveats: the result card (SVG) carries the sentence, the numbers and the caveat. The ledger row: Does fly wiring help? · build it: Add a sense: looming · method and every run: report of 5 Oct 2026.

Where in the wiring is the turn?

Added 6 Oct 2026 · made by us · brain only · pre-registered at 09:42:54 UTC before the first trial · it changes no grade

The looming test above left two questions. The scrambled brains were about half as active as the real one, so was the turn lost only because they were too quiet? And which part of the wiring carries it? We went back to the brain model alone (no body) with the same shadow and asked three things: does a scrambled map turned up to the real map's activity produce the turn command? Does scrambling only the inside of the map, while keeping every connection onto the output neurons, remove it? And does the turn need the escape neuron?

Open the share card (SVG): the sentence, the numbers, the caveats and the date on one image.

1. Pre-registered Scrambled and turned up to the real activity. We turned the scrambled maps up until they were as busy as the real one. They still did not produce the turn: the wiring, not the amount of activity, makes it. Reading by the rule: "the turn needs the wiring even at the same activity": 3 shuffles matched the real activity (gain 2.25, outside-activity 0.98 × real, whole brain 27,166–27,515 spikes vs 27,686), 0 of them produced the turn command.
2. Pre-registered Scrambled inside only (every edge onto descending, motor and endocrine neurons and out of sensory and ascending neurons kept; the rest shuffled). Scrambling only the inside of the map kept about -9% of the turn command and 69% of the escape signal. In plain words, −9% means none (the far-side command was absent in all 6); it is slightly negative because in one trial the near-side DNa02 fired 1 Hz. Readings by the rules: turn command "the turn needs the wiring in between" (fly67's DNa02 rule passed in 0 of 6); escape signal "partly" (giant-fibre retention 0.69, below the 0.9 bar for "rides on direct connections"; above 50 Hz in 6 of 6).

   Descriptive, not pre-registered Per neuron, the kept part is one side: the near-side giant fibre, which gets 832 (left) and 1,053 (right) direct synapses from the looming neurons, kept firing at 151–169 Hz (real map: 129 and 149–156 Hz); the far-side giant fibre went to 0 Hz (real map: 84–104 Hz).

3. Pre-registered Giant fibre silenced (every synapse out of both giant fibres, DNp01, set to zero; the fibres themselves still spike). With the escape neuron silenced, the turn command stayed. Reading: "steering survives silencing the giant fibre" (fly67's rule passed on both sides; far-side DNa02 changed by −2 Hz and 0 Hz against the paired real trials). This was expected from the wiring: the map has no giant fibre → DNa02 connections at all, so the test checks fly67's claim in our engine, not a hidden route.
4. Pre-registered Plain scramble (same number of connections per neuron): 6 trials over 3 shuffles, every readout 0 Hz, and the brain about 14 times quieter outside the stimulated neurons (0.07 × real).

What the map's own counts already said

Before the first trial we counted where the looming neurons' synapses go in the map. They reach the turning neurons DNa02 only through relays, the strongest being PVLP141 on the eye's side, while they synapse directly onto the giant fibre of their own side. That is why the inside-only scramble could break the route to DNa02 while the direct route to the giant fibre stayed, and why silencing the giant fibre could not touch the turn: the map has no giant fibre → DNa02 connections.

Share it with its caveats: the share card (SVG). Every trial, the gain search and the deviations: report of 6 Oct 2026 · the ledger row: Does fly wiring help?

Who does the walking?

Added 2 Oct 2026 · our own test, pre-registered · context for embodied claims; it changes no grade

"The fly brain learned to walk" is the most common embodied claim: Eon's embodied fly, the Gorilla Tag video ("learned to move around as a gorilla") and FLY67, whose browser fly turns the rates of the walking neurons P9, DNa02 and MDN into an animated walk with hand-set gains. We could not inspect Eon's or Gorilla Tag's code, so we built the setup ourselves: the Shiu et al. whole-brain model (FlyWire) drives FlyGym's walking fly, the most-used simulated fly body, through two numbers every 100 ms.

Questions to ask of a "brain walks" video: who chose which neurons to stimulate? Does the body have its own walking controller? How do neuron rates become leg commands, and who wrote that rule? Does the same body walk with a scrambled brain, or with no brain? Full test: Does fly wiring help? · build it: Add a body.

Five questions to ask about any fly brain demo

1. Which wiring does it load?

   Look for a named dataset and version, such as a FlyWire connectome release. "Inspired by the fly brain" or "based on the connectome" without a file or version is a warning sign.

   • Measured, if a real release is loaded
2. What turns the wiring into activity?

   There must be a neuron model that runs over time. If the code only draws the network, or picks neurons at random for display, the brain is decoration.

   • Modelled
3. Who chose the inputs and outputs?

   In most games, the author decides which neurons "see" the screen and which neurons press which keys. That choice can matter more than the brain itself.

   • Hand-made
4. Was anything trained, or scripted?

   A trained readout or controller can learn to play well with almost any network behind it. Animation or game code can make a fly move without any neuron firing.

   • Trained
   • Scripted
5. Was it compared with anything?

   The strongest projects compare their result with real fly experiments, or run the same test with shuffled or random wiring. If the shuffled brain does just as well, the real wiring did not help.

Our evidence grades

• ATested against data or a control

  A named connectome release runs in a neuron model, and the output is compared with real fly experiments or with a proper control such as shuffled wiring. Methods and code or data are public. A careful negative result also gets grade A.

• BConnectome runs, hand-made inputs and outputs

  The code loads a named connectome release and simulates activity that drives the behaviour. The author chose which neurons get the input and which neurons control the output. Trained readouts are allowed but flagged. No control or benchmark.

• CPartial, stand-in or decorative network

  A small hand-picked circuit with set or trained weights, a network that is not taken from the connectome, or a real connectome whose activity only triggers scripted movements. The network is not the main source of the behaviour.

• DScripted or ordinary game logic

  The behaviour comes from normal code, animation, a controller without connectome limits, or a language model. Any neurons on screen are cosmetic.

• UUnverified claim

  We could not inspect how it works: there is no code, the code does not match the claim, or there is only a video or post. We record the claim and its source.

• n/aInfrastructure

  Datasets, bodies, simulators, analysis tools and directories. We do not grade them for behaviour; they get licence, maintenance and setup notes instead.

We give the lowest grade whose conditions all hold, and we grade from code, configuration, data loading or paper methods that we inspected, never from a README headline alone.

Verdicts on viral fly brain claims

Each row splits a viral claim into its parts: what the simulated brain really does, and what a person chose, trained or scripted. We inspected the code on 28 September 2026 and re-checked the rows on 29 and 30 September and 1, 2, 3 and 5 October; the last column shows each row's latest check. On 2 October the Terraria fly was added at the top, the first viral video claim this week with code; on 1 October two video claims were added, Gorilla Tag and a Roblox fight, both without code; on 30 September the FlyLeno claim was added and the Doom row gained the autopilot sweep. Results are the authors' own numbers; we did not re-run these projects. "Watch" links open the matching cards in the Video gallery.

The pattern: a real connectome is usually loaded and simulated, but a person decides which neurons see the game and which neurons press which button. In several demos, scripts or trained parts produce most of the visible movement, and one (Half-Life) does not load a connectome at all. None of the viral game demos tests its own behaviour against shuffled wiring; the first outside test of one (DOOMFLY) found that a constant autopilot does about as well. The Pokémon-on-a-Raspberry-Pi and Rainbow Six claims publish no code at all. FlyLeno is the opposite case: its code is open and its brain really runs, but engineered layers shape most of the show. Gorilla Tag and a Roblox fight are videos with hundreds of thousands of views and no project or code behind them that anyone can inspect. The newest, the Terraria fly, is the opposite: open code and a real connectome, but no control. And our own body test shows why a walking body is weak evidence on its own: the body controller walks with or without a real brain.

Claims we could not check (grade U)

• UGorilla Tag (YouTube)

  No model, data or code is named; the only link is a page of game maps and socials, and four GitHub searches found nothing (1 Oct 2026). Re-checked 6 Oct 2026 at 899,151 views: still no code. We have not watched the video.

• UTwo fly brains fight in a Roblox game (YouTube)

  Only Discord and Roblox-group links; three GitHub searches found nothing related (1 Oct 2026).

• UPokémon on a Raspberry Pi 5 (Twitch)

  No code is public: we found no code under the creator's name, and neither the article nor the stream page links any (searched 29 Sep 2026). The input is game memory, not vision, by the creator's own account.

• URainbow Six Siege fly brain

  No code, model or write-up; known only from one news report of a social-media post, which we could read only through search summaries.

• UBeat Saber fly

  No code, weights or method were published. The author's explanation (motor output fitted to a replay of one song) is known to us only through search summaries of replies.

• UNeuroCraft Fly (Minecraft)

  The public repository holds documents, a licence and two videos. The simulation code and mod are "coming soon". The README itself says read-outs select scripted body programs.

• UEon's embodied fly

  The body and embodiment code are not released; the public Eon repository is brain-only. Eon's own description points to pre-trained controllers switched by a few hand-picked neurons.

• ULoihi 2 fly brain (Sandia)

  A preprint with no code link that we could find.

• Uflybrain.info Lab

  The in-browser Lab plays back eight pre-computed runs; the model code behind them is not published.

Common questions

Plain answers to the questions people ask most, each with its evidence and what we are unsure about. Last checked 6 Oct 2026.

Controlled tests: does the real wiring matter?

The most useful projects run the same test with shuffled or random wiring. If the shuffled brain does just as well, the real wiring did not help. We keep every such study in one ledger: 41 studies, 33 of them with a wiring null. The real wiring helps in 15, makes no difference in 8, does worse in 2, gives mixed results in 7, and 1 is not yet scored. New on 6 Oct 2026: our looming test is now "helps" with a fair null and strong method by our fixed rules, after the activity-matched scramble; fly tennis and FlyBrain Flappy ("helps", one shuffle each, weak), Fly-Racer ("mixed"); and Fly Dino corrected: a network with no connectome does as well.

• Reflexes, senses and steering: mostly yesFor fly-like reflexes, such as sugar taste driving the feeding neuron, for sensory circuits and for steering a simulated body toward a target, the real wiring beats scrambled wiring. It is a low bar: most of these tests ask whether a pathway still carries a signal after rewiring.
• Trained, reservoir and ML tasks: noFor reservoir computing, hashing, chess (two studies) and trained Doom players, the fly wiring did no better than shuffled wiring, and sometimes worse. The one machine-learning exception, a redesigned CartPole flight circuit (3 Oct 2026), beats its shuffled wiring but ties its own linear map. And in Doom, a brainless autopilot plays about as well as the untrained fly brain.

Only 13 of the 41 studies reach "strong" method quality, every number except our own three tests is the authors', and none is replicated. Our own pre-registered reflex test counts as "mixed" with an unfair null and weak method by our fixed rules, because its gain-matched check did not match on 3 shuffles; no rule was changed to rescue it. The chart, the counts by task family, a filterable table of all 41 studies with links, and a checklist for fair controls are on Does fly wiring help? The table that stood here until 29 Sep 2026 (20 studies) is replaced by that ledger.