Leading neuroscientist Vilayanur S Ramachandran shares intriguing case studies revealing the powerful, adaptive potential of the human brain. Among them the case of the 70-year-old engineer who felt much better after acting on a life-long urge to have his left arm amputated below the elbow. Brain-imaging experiments showed that with this particular patient, the hand on this genetic map was missing – so the sensory impulses from the arm had nowhere to go to, and the patient experienced it as "over-present". Similar changes in body images might even explain the desire that transsexuals have to have their penis amputated.