A New Sensation

A 28-year-old man who has had paralysis for more than ten years due to a spinal cord injury has been able to “feel” physical sensations through a prosthetic hand directly connected to his brain, and even identify which mechanical finger is being gently touched. The advance was made possible by neural technologies developed under the U.S.’s Defense Advanced Research Projects Agency’s (DARPA’s) Revolutionizing Prosthetics (RP) program.

“We’ve completed the circuit,” said DARPA program manager Justin Sanchez, PhD. “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 biotechnological restoration of near-natural function.”

The clinical work involved the placement of electrode arrays onto the volunteer’s sensory cortex - the brain region responsible for identifying tactile sensations. In addition, the team placed arrays on the volunteer’s motor cortex, the part of the brain that directs body movements. Wires were run from the arrays on the motor cortex to a mechanical hand developed by the Johns Hopkins University Applied Physics Laboratory (JHU APL). That gave the volunteer the capacity to control the hand’s movements with his thoughts, a feat previously accomplished under the DARPA program by another person with similar injuries.

Then, breaking what DARPA calls new neurotechnological ground, the researchers went on to provide the volunteer a sense of touch. The JHU APL hand contains torque sensors that can detect when pressure is being applied to any of its fingers and can convert those physical “sensations” into electrical signals. The team used wires to route those signals to the arrays on the volunteer’s brain.

In the very first set of tests, in which researchers gently touched each of the prosthetic hand’s fingers while the volunteer was blindfolded, he was able to report with nearly 100 percent accuracy which mechanical finger was being touched. The feeling, he reported, was as if his own hand were being touched.

“At one point, instead of pressing one finger, the team decided to press two without telling him,” said Sanchez, who oversees the RP program. “He responded in jest asking whether somebody was trying to play a trick on him. That is when we knew that the feelings he was perceiving through the robotic hand were near-natural.”