Sunil, Benali, and Moutuou map the C. elegans nervous system as a multiplex: one layer of fast synaptic wiring, one layer of slow extrasynaptic neuropeptide diffusion. The standard assumption is that function follows wiring — you are who your neurons connect to. The multiplex framework reveals four regimes, and the most interesting one violates this assumption.
Topology-dependent circuits reinforce motor control. Purely synaptic pathways handle rapid sensorimotor processing. These do what wiring diagrams predict. But a third regime — topology-resilient modulation — maintains behavioral regulation regardless of specific anatomical connections. The extrasynaptic layer doesn't care who is wired to whom. It diffuses through tissue, reaching targets by proximity rather than connectivity. The result is a communication channel whose function is decoupled from the structure that nominally defines the system.
The fourth regime is purely extrasynaptic homeostasis, sustaining survival functions through diffusion alone.
The structural claim: a nervous system needs both topology-dependent and topology-resilient communication because they solve different problems. Speed requires dedicated wiring. Robustness requires broadcasting that persists even when specific connections are damaged or absent. The two modes don't compete — they occupy complementary niches, specialized for different failure modes.
This is the same architecture as the neuropeptide atlas that mapped cortical-subcortical gradients and found neuropeptide expansion tracking neocortical complexity. The modulatory system scaled precisely because it was the part that didn't need specific wiring. The less it depends on topology, the more easily it expands. The channel that doesn't care about structure is the one that survives structural change.