“We’ve completed the circuit,” said DARPA program manager Justin Sanchez. “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.”
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.
Science fiction movie lovers were shown this idea at the end of the 1980 film Star Wars Episode V: The Empire Strikes Back (*spoiler alert!*). In the film's final battle, Darth Vader cuts Luke Skywalker's hand off. It is replaced by droid surgeons. In the video below, the robotic hand demonstrates sensation when poked by the surgeon (start at about 0:20 seconds below):
(Start 0:20 seconds to see Star Wars robotic hand sensation)