Fly Learning — Pavlov on the real wiring

Kenyon cells — the odour, written as a sparse code

γ lobe α/β lobe α'/β' lobe firing now

Smelling: fresh air

All 4,064 Kenyon cells, one square each. An odour is a set of 13 olfactory glomeruli; a Kenyon cell fires only when several of its five-or-so projection-neuron inputs agree, and the APL neuron's feedback keeps it to a few per cent of cells — so each odour lights a different constellation. Those constellations are what the fly learns about.

Controls — the experiment

What it thinks of← avoidapproach →

Neurons (PN / KC / MBON / dopamine)—

Synaptic connections · plastic ones—

Kenyon cells firing now—

Synapses depressed (the memory)0

Sim step rate—

The rule: pick an odour, then hold sugar or shock. Dopamine neurons (PAM for reward, PPL1 for punishment) each cover one compartment of the mushroom body; dopamine arriving while the compartment's Kenyon cells are active depresses those KC→MBON synapses. Reward compartments belong to avoidance-driving MBONs, so odour + sugar = less avoidance = the fly now likes it. Test it: present the odour alone and watch the marker. Then test another odour — it should be untouched.
What is real: every cell, transmitter and synapse count; which dopamine class covers which MBON (read from the wiring, not hand-labelled). What is tuned: a handful of gains. What is new: this is the first thing on this box that learns — and it learns at the one synapse evolution made plastic. Keys: 1 2 3 odours, 0 air, hold S sugar, X shock.

The brain in 3D — all 4,733 cells, their real shapes, lit by the simulation

Kenyon cells, γ lobe Kenyon cells, α/β Kenyon cells, α'/β' projection neurons (the odour comes in here) MBON, approach MBON, avoid PAM (sugar) PPL1 (shock) loading skeletons… brightness

The reconstructed skeletons of every neuron in the simulation. Present an odour and the projection neurons flash first, then a sparse scatter of Kenyon cells lights up along the lobes — that is the odour, written in cells. Hold sugar and the PAM neurons blaze across the horizontal lobes; hold shock and the PPL1 neurons do. Drag to turn, scroll to zoom.

Fly Learning — Pavlov on the real wiring

Kenyon cells — the odour, written as a sparse code

Controls — the experiment

The brain in 3D — all 4,733 cells, their real shapes, lit by the simulation

Where the memory lives — depression at each output neuron's Kenyon-cell synapses