Areas of a brain can be irreparably harmed in a variety of ways. One of the more devastating is a stroke. A stroke causes a loss of brain function due to disrupted blood supply to the brain. Often the neurological damage is permanent: part of the brain dies.
American psychologist Shepherd Franz was interested in brain functioning. By 1915 Franz had demonstrated that patients paralyzed by strokes, some for as long as 20 years, could partly recover functionality with the aid of brain-stimulating exercises. The exercises were aimed at gradually restructuring the brain.