Research on prosthetics takes its greatest strides during or just after wartime, and the past several years have sadly been no exception. Todd A. Kuiken of the Rehabilitation Institute of Chicago and his team have pioneered “targeted reinnervation,” which jacks an artificial arm into the nervous system. They transplant nerves from the shoulder of a lost arm to a patch on the chest. In trying to move the arm, the person causes chest muscles to flex, which electrodes pick up and transmit to the prosthesis. The researchers have begun to experiment with two-way connections, relaying signals from sensors on the arm to sensory nerves.