What drives the feeding reflex?

Watching which neurons fire alongside a behavior is not the same as knowing which ones cause it. This page runs both tests on the whole fly brain model and checks the model against real flies.

Correlation is not causation

Each dot is one neuron that fires when the fly tastes sugar. Across: how closely its firing tracks the proboscis motor neuron MN9 over time. Up and down: how much MN9 drops when that one neuron is silenced in the full-brain model. Many neurons track MN9 closely but change nothing when removed. A few change everything. Click a dot to open it in the lab.

Both axes are model activity, not recordings. Correlation: best Pearson r of 10 ms binned rates over lags from −50 to +50 ms, 10 trials. Silencing: mean MN9 rate over 10 trials with the neuron's outgoing synapses set to zero, as in Shiu et al. 2024.

More sugar, more drive

MN9's firing rate as the sugar neurons are driven harder. The shape is a threshold then a climb, not a switch.

Bitter vetoes sugar

Bitter neurons on the same side as the sugar neurons (cell_sub_class “bitter”). In real flies bitter taste suppresses feeding; the model reproduces the veto from the wiring alone.

Does the specific wiring matter?

Scorecard against real flies

Shiu et al. switched on 106 taste-circuit cell types one at a time in living flies with light (optogenetics) and recorded whether the fly extended its proboscis. Here the same 106 activations run through this lab's engine, and each prediction is scored against what the real flies did (Fig. 2, Supplementary Table 3).