Three main causes for the inability of injured nerves of the central nervous system, or CNS, to regenerate have been known to date: the insufficient activation of a regeneration program in injured nerve cells that stimulates the growth of fibers, so-called axons; the formation of a scar at the site of injury that is difficult for nerve fibers to penetrate; and an inhibitory effect of molecules in the nerve on regrowing axons. “Although experimental approaches have been found in recent decades to address these individual aspects by therapeutic means, even combinatorial approaches have shown only little success,” says Fischer. “So there must be other yet unknown causes for why nerve fibers in the CNS don’t regenerate.”