When an arm or leg is amputated, patients often continue to feel vividly the presence of the missing limb as a "phantom limb" (an average of 80%). Building on earlier work by Ronald Melzack (McGill University) and Timothy Pons (NIMH), Ramachandran theorized that there was a link between the phenomenon of phantom limbs and neural plasticity in the adult human brain. To test this theory, Ramachandran recruited amputees, so that he could learn more about if phantom limbs could "feel" a stimulus to other parts of the body.