Want a True Bionic Limb? Good Luck Without Machine Learning

In 2006, the Defense Advanced Research Projects Agency vowed to build, within four years, a brain-controlled prosthetic arm indistinguishable from the real thing. Yet after hundreds of millions of dollars and more than a decade of engineering, most limb replacements (even those wired straight to the noggin) struggle to mimic human gestures. Cracking the neural code for movement was trickier than expected. The trouble lies in getting past conscious thought. "Capturing the body's innate ability to just know what to do is something really lacking from all prosthetics today," says Mike McLoughlin, who manages the prosthetics program at Johns Hopkins.