RTN4 and brain injury: Newly sprouting fibers from corticospinal tract form a compensatory network via propriospinal neurons, and thereby contribute to functional recovery.1 So far, enhancement of fiber sprouting from the corticofugal tract after brain injury has been accomplished in animal models by providing neurotrophic factors18, 19 and antibodies to axon growth inhibitors (NogoA),20 and modulating of neural activity.21 In the present study, we identified an additional candidate molecule, PHD, as an important regulator of axon rewiring after brain injury.