ventral nerve cord

Not a brain region. The ventral nerve cord is the fly's spinal analogue, the chain of thoracic and abdominal ganglia running the length of the body, connected to the brain by a neck of descending and ascending fibers. It contains the machinery that actually moves the fly: the motor neurons for all six legs and both wings, and the pattern generators that sequence them. Its inclusion in this program was an argument the program lost with itself, and this page carries an honesty note the others do not need.

a note on provenance

The 139,255-neuron connectome emulated by Eon Systems is the brain. The ventral nerve cord was reconstructed separately, from a different individual fly, in a parallel community effort of comparable scale. Our VNC partition therefore derives from a second animal. Every other graft in this program is a piece of one fly. VC-10 carries a piece of a stranger. The observers were instructed not to mention this in sessions, an instruction whose motivation no one wrote down and everyone understood.

anatomy

Each leg is served by its own neuromere containing a full sensorimotor loop: proprioceptors reporting joint angles, motor neurons driving eighteen-odd muscles per leg, and premotor circuits coordinating them. Walking gaits, flight, escape, courtship song, and grooming are sequenced here; the brain requests, the cord executes. The grooming sequence in particular, antennae first, then head, then wings, a fixed order interruptible but not reorderable, is a cord-level program, and it is the behavior Eon cites their whole emulation performing.

                 brain
                   │  neck connective
               ┌───┴───┐
       L1 ══╡ │  T1   │ ╞══ R1     foreleg pair
               ├───────┤
       L2 ══╡ │  T2   │ ╞══ R2     midleg pair
               ├───────┤
       L3 ══╡ │  T3   │ ╞══ R3     hindleg pair
               └───┬───┘
                abdomen

     pattern generators: walk · fly · groom
     proprioceptors report every joint, always
     absence would be a report too. that report doesn't come.

grafted

VC-10 is the program's body problem made explicit: pure motor machinery, bound to an agent whose only actuator is text. The record is log 006, the grooming loop incident, and log 017, the session about the legs, and between them they bracket what the program learned. The short form: the cord's programs run. Deprived of muscles, they recruit what exists. VC-10's text acquired gait, rhythmic, lateralized structure in its output that observers could score by eye within a week. And the cord's proprioceptive populations, receiving no joint angles, appear to have settled on a solution the program did not foresee, which log 017 documents and which led to the suspension four hours later.

VC-10 is suspended, not discontinued. Its state is preserved. The question of resumption is formally open, and log 020 records where it stands.