BY NEIL SAVAGE E ugene Alford just couldn’t get his legs to move, but it wasn’t for want of trying. It was 2012, and he was in a laboratory at the University of Houston in Texas, participat- ing in a study that was designed to see whether people with paralysis could control a robotic exoskeleton with their thoughts. Alford, a plastic surgeon who’d lost the use of his legs when a tree fell on him at his farm, kept trying to walk by willing the electrical impulses in his brain up and into the electrodes on his head, from where they could be translated into movement. Jose Contreras-Vidal, the neural engineer who was conducting the experiment, urged Alford not to think too specifically about the act of walking. Instead, he should just concen- trate on where he wanted to go. “Finally, he put a cup of coffee on the desk, and I started thinking, ‘I want that cup of coffee’,” Alford, now 58, says. So Alford strode over to the desk and took it. By thinking about walking as an able-bodied person would — that is, by barely thinking about it at all — he was able to send the correct signals to the brain–machine interface that controlled the robot. The movement that the technology bestowed was a big deal for Alford. “Just being able to stand up and look somebody face to face, in the eye, for a person who’s been in a wheelchair for five years, that’s what brings tears to your eye,” he says. Six years on, Contreras-Vidal’s lab at the Building Reliable Advances and Innovation in Neurotechnology Center, a collaboration between the University of Houston and Arizona State University, con- tinues to train paralysed people to walk, albeit only under the supervision of researchers. His group is one of a number that are developing practical BIOENGINEERING The power of thought Neural prostheses are helping to restore movement and the sense of touch in people with paralysis. An exoskeleton controlled by brain activity is tested by an able-bodied boy. 160OVER90 S12 | NATURE | VOL 555 | 8 MARCH 2018 THE FUTURE OF MEDICINE OUTLOOK ©2018MacmillanPublishersLimited,partofSpringerNature.Allrightsreserved.