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Neurotrophic hypothesis

Marcus Singer's mid-20th-century finding that vertebrate limb regeneration strictly requires nerves. Amputate a salamander limb that has been denervated and the wound merely scars — the blastema fails to proliferate. Crucially the effect is quantitative: enough nerve fibers per unit of wound area, whether motor or sensory, will do. The molecule nAG, secreted by nerve sheaths, was later identified as the signal that sustains the blastema. This is why a neural interface — like the kuru — is the ideal channel through which an outside network could supply the signals that direct growth.