Fly connectome study suggests path-integration memory lives in synapses, not neural activity

viksit · x · 2026-09-15

An exhaustive pass over every fan-shaped-body population in the MaleCNS (2026) and hemibrain (2020) fly connectomes yields four findings: the long-sought path-integration "sum" is probably stored in synapse strengths at hΔB's outputs rather than sustained loop activity (challenging standard RNN/LLM-style state models); every memory store delivers displacement sign-preserved, with only hΔM and hΔI acting as inverters on the return path; the velocity signals come from cells nobody has named yet (e.g. PS196b feeding ExR2, ExR4, LPsP, FB3A); and the compass has a built-in brake—shifter neurons get 3x more input from the position they write than the one they read—absent from all published navigation models. Each claim is tagged as published, simulated, or hypothesis.

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