Experience of phantom limbs lets amputees control real replacements

IN THE EARLYTMR 16th century a knight called Gottfried von Berlichingen spent decades marauding and feuding on behalf of the Holy Roman Empire. He conducted most of his career singlehandedly—the other having been blown off by a cannonball. To replace it he had a metal duplicate made, with spring-loaded fingers that could hold a sword, shield or the reins of his horse. This early prosthetic device gave him the nickname “Götz of the Iron Hand”.Prostheses have come a long way since Götz’s day. A technique called targeted muscle re-innervation () permits surgeons to take the nerves that once controlled a missing limb and attach them to muscles in a patient’s chest or back. The redirected nerves grow into their new muscular homes. These then act as signal amplifiers: a muscle’s electrical activity reflects that of the nerves supplying it, but is far more powerful and therefore easier to detect using external electrodes. That activity, duly interpreted by computer, can be used to drive motors within the prosthesis to make it do what its wearer wants.