Researchers have worked for years to develop a prosthetic limb controlled by the brain or myoelectric activity. For now, many still prefer the old prosthetics that use centuries-old technology:
Watching the arm intently as it goes through these motions, Lehman imagines his missing arm moving in the same way. This focused mental exercise triggers neuromuscular activity in his stump that the electrodes pick up. A cell-phone-sized computer velcroed onto the sling behind Lehman’s shoulder correlates the arm’s vocabulary of motions to Lehman’s desires. The hand pinches closed, Lehman tries to tell his missing hand ‘pinch,’ and the computer remembers the muscle activation that his thought engenders. He has to go through this routine every time he straps on the arm because the sensors never end up in exactly the same place. Lehman’s stump changes from day to day, too. He sweats. His skin stretches. His muscles swell and shrink. And, more fundamentally, Lehman’s brain changes. Tomorrow he might visualize his arm movements differently.