The result is a condition called focal hand dystonia, in which the sufferer cannot raise her forefinger, for instance, without the middle finger's curling or rising up too. She is exploiting neuroplasticity to retrain the cortex. By having patients trace designs on first one finger, then another, and handle little objects like buttons or keys, Byl trains their brains to process input from each finger separately once again. Cortical retraining also holds out hope for more common afflictions. The idea is to perform the neural version of an electrician's wiring a shunt around the damaged part of an electrical circuit.
Plasticity is also the basis for a promising new therapy for stroke.
Psychologist Edward Taub of the University of Alabama at Birmingham reasoned that if you constrain the unaffected arm of a patient whose stroke has immobilized the other arm, he would have to stop coddling the affected arm. CI therapy, says Taub, seems to recruit intact areas of the brain to take over from damaged regions in this case, regions responsible for moving an arm. The only thing it does is induce repetitive use of the affected limb, which in turn induces cortical reorganization. The area responsible for producing movements of the affected arm more than doubles in size. CI therapy has restored function to patients as much as 21 years after their strokes.