In rate models of two fly connectomes, measured head-direction wiring held ring-ordered bumps after class gain tuning and 40 shuffles did not, but bumps locked to 3-9 headings and seldom turned

Question: is the measured neuron-level wiring of the fly head-direction circuit sufficient to hold and turn an activity bump if a model sets only class-level gains, and is the answer the same in two animals? Approach: we built rate models of the core circuit (EPG, EPGt, PEN_a, PEN_b, PEG, Delta7, P6-8P9; 156 to 159 neurons) from hemibrain v1.2 and FlyWire v783. Weights are synapse counts divided by the total input of the target. The transmitter class sets the sign. We tuned 5 pathway gains and 3 drives with equal search budgets for the measured wiring and for 20 type-preserving shuffles per animal. Results: after tuning, the measured wiring held a cue-set bump in all 8 searches (best scores 0.93 hemibrain, 0.89 FlyWire). None of the 40 shuffles held a coherent bump (rank p = 1/21 per animal). A label-free check showed bump-shaped, ring-ordered states only for the measured wiring (Spearman ring order 0.63 to 0.85). Some shuffles held unordered cue-specific states. Gains tuned in one animal held bumps in the other in 3 of 4 transfers each way. The bumps locked to 3 to 9 stable headings, not to a continuous ring. Asymmetric PEN drive turned no FlyWire model. It turned 2 of 4 hemibrain models tuned also for rotation, with a threshold and a non-linear speed curve. All turning agreed with the direction that the PEN output offsets predict. Limitations: simple rate model without ring-neuron input or synaptic dynamics; random local search with 200 evaluations; uncalibrated time constant; FlyWire and hemibrain synapse counts differ about threefold; 20 shuffles per animal limit p to 0.048.

Drosophila · head direction · ring attractor · central complex · connectome · FlyWire · hemibrain · EPG · PEN · Delta7 · rate model · structure-function