The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science

by Norman Doidge

Then Taub had another epiphany, the one that would transform the treatment of strokes. He proposed that the reason a monkey didn’t use its arm after a single limb was deafferented was because it had learned not to use it in the period right after the operation when the spinal cord was still in “spinal shock” from the surgery. Spinal shock can last from two to six months, a period when the neurons have difficulty firing. An animal in spinal shock will try to move its affected arm and fail many times during those months. Without positive reinforcement, the animal gives up and instead uses its good arm to feed itself, getting positive reinforcement each time it succeeds. And thus the motor map for the deafferented arm—which includes programs for common arm movements—begins to weaken and atrophy, according to the plasticity principle of use it or lose it.