Clinical deficits after injury to the CNS are due, in large part, to dysfunction of white matter (myelinated fiber tracts), including descending and ascending tracts in the spinal cord. A crucial set of questions, in the search for strategies that will preserve or restore function after CNS injury, centers on the pathophysiology of, and mechanisms underlying recovery of conduction in, CNS white matter. These questions are relevant both to spinal cord injury, and to brain infarction, which frequently affects white matter.