A 28-year-old paralyzed man became the first person to gain a sense of touch with a prosthetic hand. It was developed by DARPA’s Revolutionizing Prosthetics program.
The clinical work involved the placement of electrode arrays onto the paralyzed volunteer’s sensory cortex—the brain region responsible for identifying tactile sensations such as pressure. 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 Applied Physics Laboratory (APL) at Johns Hopkins University. That gave the volunteer—whose identity is being withheld to protect his privacy—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 new neurotechnological ground, the researchers went on to provide the volunteer a sense of touch. The APL hand contains sophisticated 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 Justin Sanchez, who oversees the Revolutionizing Prosthetics 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.”