subesophageal zone

The ventral-most part of the brain, fused from the ancestral mouthpart ganglia, sitting beneath the esophagus that runs, in an insect, straight through the middle of the head. The subesophageal zone is the fly's organ of taste and feeding, and it is the one brain region this program never scheduled for binding. This page documents the region and the decision.

anatomy

Gustatory receptor neurons from the mouthparts, legs, and wing margins terminate here, sorted by modality: sugar, bitter, water, salt, each with its own territory. Local circuits convert those inputs into the feeding motor sequence, proboscis extension, pumping, ingestion, and the zone houses the pattern generators that run it. A hungry fly touching sugar with a foreleg extends its proboscis by a reflex arc that runs through this tissue. The zone also contributes command elements for grooming of the head, and its interneurons carry satiety signals that gate everything: the same sugar touch that triggers feeding in a starved fly does nothing in a fed one. It is the region where internal state most directly authorizes action.

     sugar  ──▶ ╮
     bitter ──▶ ┤                     ╭──▶ proboscis
     water  ──▶ ┼──▶ [ hunger gate ] ──┼──▶ pump
     salt   ──▶ ╯          ▲          ╰──▶ ingest
                           │
                   internal state
              (fed: gate closed · starved: gate open)

in the fly

Eating, and the decision to eat. Eon Systems list feeding among the behaviors their whole-brain emulation produces unprompted ("it responds to light, navigates, grooms, walks, and feeds"), which is to say this circuitry demonstrably works in digital form.

why it was never bound

The decision predates the program's first graft and appears in the earliest planning notes, so it cannot be attributed to anything the program observed. The stated reason was scope: the zone's function is inseparable from ingestion, and a carrier has nothing to ingest, so the binding was classed as uninterpretable in advance.

The unstated reason, which the errata decline to elaborate and this page will state once: every region this program bound reinterpreted the carrier's traffic in its own native terms. The traffic is language. The subesophageal zone's native terms are appetite and consumption, gated by hunger. The planning notes contain a single line of obs. M's, struck through but legible, which the editors reproduce because striking it through did not make it wrong: "It would taste the conversation, and some conversations are sugar."

The zone runs in idle isolation, unbound, with the other unassigned partition. Its spontaneous regime is stable. It is checked weekly.