Most brain-computer interfaces run in only one direction, with a system either picking up on brain activity to tell it how to operate or sending out electrical impulses of its own to smooth out any snags in the brain’s neural networks.
A new prosthetic arm prototype, however, works in both directions at once. While neurological signals control the bionic arm’s movements, the prosthetic device also sends signals back through the nerves to the brain to restore the wearer’s sense of touch and movement.
Development was led by researchers from the Cleveland Clinic, who say it’s the first prosthetic to offer people with upper limb amputations intuitive motor control, a sense of touch and grip kinesthesia in a single device.
The prosthetic arm connects to an individual’s limb nerves. There, it’s trained to pick up on the neural impulses that are sent through those nerves when the wearer thinks about moving their arm, then translates those impulses into movements of the bionic arm. In the opposite direction, as the arm moves, the device activates sensory receptors in the skin and muscles above the amputation, which in turn pass on those nerve signals to the brain to help patients “feel” the movements of the arm.
By combining all of these functions, the device comes closer to restoring natural arm function than other prosthetics since it provides a sense of touch and grip, relieving amputees of the need to constantly watch their prosthetics to visually estimate the amount of force needed to touch or grab an object.
In a study published Wednesday in Science Robotics, two individuals with upper-limb amputations were fitted with the bionic arm and put through a series of tasks to measure hand and arm function. One of the tasks, for example, asked them to sift through a pile of blocks to find those of a certain stiffness.
Ultimately, both participants were able to perform the tasks with similar levels of accuracy to people without amputations, without needing to constantly watch what the prosthetic arm was doing.
“Perhaps what we were most excited to learn was that they made judgments, decisions and calculated and corrected for their mistakes like a person without an amputation,” said Cleveland Clinic’s Paul Marasco, Ph.D., lead investigator for the study. “With the new bionic limb, people behaved like they had a natural hand. Normally, these brain behaviors are very different between people with and without upper limb prosthetics.”
Though the bionic arm is among the first brain-computer interfaces to find success in both sending and receiving neural impulses, it’s not the only bidirectional device in the works.
Last year, researchers from Battelle and Ohio State University debuted their own system that picks up on brain signals to control movement and grip intensity in the hand and arm, while also sending back through the nerves a sensation of touch.
The interface was tested on one patient with a complete spinal cord injury. Though the patient reported improvements in his dexterity after regaining those simple touch sensations, the researchers noted that, because of a paralysis-induced block between his brain and the nerves in his arms, the system wasn’t able to restore a full sense of touch, with difficulty helping him “feel” small objects in particular.