"In a woman who had lost her left arm in a car accident and four other amputees, they took the nerves that used to control elbow, wrist and finger movements and surgically threaded them into muscles in the chest. Once the patient healed, the scientist placed electrodes on the area of the chest above those muscles, and recorded the electrical signals through the skin. The signals from those nerve endings were then routed to a computer that interprets them, using them to control the motion of a prosthetic arm."
http://www.the-scientist.com/blog/display/55424/