After 31-year-old Zac Vawter lost part of his leg in a motorcycle accident, a team of doctors set out to create a new kind of prosthetic limb: one whose motions he could manipulate with his mind, by “flexing” a foot that was no longer there. The method is similar to one already tried in people who have lost an arm: The doctors at Northwestern University and the Rehabilitation Institute of Chicago removed nerves from damaged muscle in Vawter’s amputated leg and connected them to hamstring muscle in his thigh, which had been left intact. When Vawter imagined moving his missing lower leg, his thoughts caused various contraction patterns in the upper leg that remained. Electrodes stuck onto his skin picked up the signals and relayed them to sensors on the prosthesis (above), which interpreted how he wanted to move. The outcome, described today in The New England Journal of Medicine, wasn’t perfect. Vawter occasionally stumbled, but he was able to walk safely outside, climb down stairs, and kick a ball . The authors note that there are still challenges to refining the technique, in part because the electrodes can get uncomfortable.