Todd Kuiken is a doctor and engineer at the Rehabilitation Institute of Chicago. He builds new prosthetics that connect with the human nervous system, so they can be controlled by the same impulses from the brain. He does this with a technology called targeted muscle reinnervation. It uses nerves remaining after an amputation to control an artificial limb, linking brain impulses to a computer in the prosthesis that directs motors to move the limb. An unexpected effect in some patients: Not only can they move their new limb, they can feel with it.