New Prosthetic Arm Can Restore Lost Sense of Touch, DARPA Claims

15 September 2015

The limb, developed by Applied Physics Laboratory (APL) at Johns Hopkins University. (DARPA)

The latest mind-controlled, robotic arm can send sensations of touch directly to the user’s brain, according to reports from the US Defense Advanced Research Projects Agency (DARPA). In essence, they claim, it allows its user to feel things with their robotic hand.

In tests, a 28-year-old subject — paralyzed by a spinal injury for more than a decade — was reportedly able to tell which finger of his prosthetic was being touched with 100 percent accuracy. According to the volunteer, the sensation was like his own hand was being touched.

The results, which were announced at on Thursday at DARPA’s Wait, What? conference, are still in the process of being peer reviewed for journal submission. Until others in the field are able to evaluate the data from the experiments, its hard to say just how much DARPA has accomplished. But if they’re able to reproduce this 100 percent success rate — or even something close to it — in other volunteers, it could represent a big step in the development of robotic limbs. Only one other research group has ever claimed success close to this in the pursuit of sensation, back in 2014.

A patient uses an earlier version of the arm. (DARPA)

The new mechanical limb, which was created by the Applied Physics Laboratory (APL) at Johns Hopkins University, is wired directly to the brain. When you touch an object, different sensations of temperature and pressure get sent up neural pathways in your spinal cord. Once they all make it to your brain, the sensation of the object is created. By connecting the new limb to the parts of the brain that control movement and touch, DARPA researchers were able to send signals of pressure — collected by sensors on the prosthetic fingers — right where they’re supposed to go.

“We’ve completed the circuit,” DARPA program manager Justin Sanchez said in a statement. “Prosthetic limbs that can be controlled by thoughts are showing great promise, but without feedback from signals traveling back to the brain it can be difficult to achieve the level of control needed to perform precise movements. By wiring a sense of touch from a mechanical hand directly into the brain, this work shows the potential for seamless bio-technological restoration of near-natural function.”

Indeed, DARPA isn’t the only group making great strides in so-called “mind controlled” prosthetics. But this is the first time a limb has provided feedback in the other direction, sending electrical signals back to the brain to simulate an outside force.

It may sound kind of sentimental to want your robotic arm to feel touch, but quality of patient life aside, it’s actually very important to the functionality of the limb. One of the biggest difficulties in creating a successful robotic limb is making sure it can actually grasp and move objects as needed, which is difficult to do when the user can’t sense that they’re touching an object, or how hard they’re squeezing it.