the fly brain lab

A brain the size of a poppy seed, taken apart.

flylabs is a lab for the fruit-fly brain. Click through its regions, look up the neurons by name, and play with the circuits themselves — the motion detector that reads movement, the ring that holds a heading, the neuron that fires the escape.

139,255neurons mapped
54.5Msynapses
20neurons in the index
fly brain · live visualisation
spikes / s
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optic lobe ← central brain → optic lobe
move your cursor to stimulate it
brain time
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01 · the brain

Five regions, one poppy seed.

Pick a region to light it up. Everything in the fly's head has an address, and every address has a job.

whole brain
click a region · drag to stimulate
02 · the index

Neurons, by name.

Each one is a real, named cell type in the fly brain — what it sees, what it computes, and how fast it answers.

03 · circuits

Run the circuits yourself.

Three famous fly circuits, implemented as they were published — and wired to your cursor.

drag across the strip · or press play
CIRCUIT 01

The motion detector

T4 · T5 · Hassenstein–Reichardt, 1956

Two neighbouring photoreceptors, one of them delayed, multiplied together. Do it in both directions and subtract: what survives is motion. T4 correlates brightening edges, T5 darkening ones.

T4 · ON
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T5 · OFF
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no motion
click or drag around the ring
CIRCUIT 02

The compass ring

EPG · Δ7 · central complex ring attractor

Sixteen EPG neurons tile 360°. Neighbours excite each other, Δ7 cells inhibit everyone, and the network settles into a single bump of activity — the fly's sense of which way it is facing. Push it and it follows; let go and it holds.

bump height
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Δ7 inhibition
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heading —
something is coming
CIRCUIT 03

The escape

LC4 · LPLC2 · Giant Fiber (DNp01)

Looming cells don't measure size, they measure how fast size is growing. When that rate crosses threshold the Giant Fiber fires once — and the fly is airborne before you finish moving your hand.

LC4 · looming
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GF · escape
quiet
watching
04 · facts

Small brain, hard numbers.

Everything here comes from published work on Drosophila melanogaster.

139,255neurons in the whole adult brainFlyWire connectome · Nature, 2024
54.5Mchemical synapses between themFlyWire connectome · Nature, 2024
~8,400annotated cell types — each one findable by nameFlyWire cell-type annotation
~2,000Kenyon cells per hemisphere; roughly 5% fire for any one odoursparse coding in the mushroom body
16EPG wedges tile a full 360° of headingcentral complex ring attractor
4 + 4T4 and T5 subtypes — one per cardinal directionON and OFF motion pathways
1 spikefrom the Giant Fiber is enough to launch a takeoffescape pathway
~0.2 mm³is roughly the volume all of it fits intosmaller than a poppy seed
Honest label. The glowing brain and the three circuits are simulations running in your browser: real published algorithms and real anatomy, drawn schematically. They are not a neuron-by-neuron model of a real fly, and the animation is art on top of the maths.