Amputees may soon be capable of feeling sensations in their lost limbs, thanks to an advanced set of prosthetics capable of being controlled by the human mind. The US military’s research wing, known as the Defence Advanced Research Projects Agency, has studied prosthetics for the past decade and has now developed arm patients can control using their thoughts.
Patient Melissa Loomis, 43, who lost her right arm after she was bitten by a wild raccoon, underwent two specialized forms of surgery, Quartz has reported. The first was targeted muscle reinnervation, or TMR, which re-routed the three major nerves originally controlling Ms. Loomis’ hands and fingers – median, ulnar and radial – to power muscles in her upper right arm.
This fools the brain into thinking her bicep or tricep is now essentially her forearm – allowing her to move her prosthetic has as if it were her real hand. The second type of surgery, known as targeted sensory reinnervation, was developed to aid the transmission of sensations, such as touch, back to her brain.
This involved locating nerve fibers from within the three nerves and attaching them to cutaneous nerves in the stump of her arm. This means pressing the thumb of the prosthetic would trigger the sensation of pressure on her thumb.
Ms. Loomis had been suffering with phantom limb syndrome – a fairly common affliction among people who have lost limbs, which causes them to feel pain in the hand she no longer had. “It felt like my hand was crushed in a vice like there was an object closing my hand that I was constantly trying to break free of,” she said.
“I could feel the hand but it was like I couldn’t open my fingers like it was in a tight fist. After the surgery, it felt like I could move my hand, and the pain went away.” Her surgeon Ajay Seth collaborated with teams from the University of Alberta in Canada and the National Military Medical Centre to test Ms. Loomis’ control over a prosthetic arm, which is not attached to her body.
The large arm was positioned several feet away from Ms. Loomis at a laboratory in Baltimore, where she was able to both move the arm and hand using her mind, and feel when somebody touched its fingers.
She described the feeling as “a tingling sensation – like putting your tongue on a battery. You could feel it jolt up the finger.” As well as sensations, she can theoretically detect changes in temperature and pressure.