Prosthetic hand now able to “tell” brain what it is touching
This prosthetic might be able to communicate a sense of touch to its user

Prosthetic hand now able to “tell” brain what it is touching

Research on prosthetic hands has come a long way but most of it was focused on improving the way the body controls the device.

At this point in time, it may also be possible for prosthetic hands to send signals back to the body and “tell” it about what the bionic hand is touching.

Research at DARPA (Defense Advanced Research Projects Agency), the research arm of the U.S. military, implanted an array of small electrodes into regions of the brain that controls movement in a woman who is paralyzed. The electrodes communicated electrical activity from the brain’s motor cortex, via wires, to a prosthetic arm that the woman was able to move through a wide range of motions.

The research team then asked if they could run the experiment in reverse and if they could do for sensation what they did with the motor system, according to Justin Sanchez, program manager of the DARPA biological technologies office, in a presentation he gave at the Wait, What? A Future Technology Form, which DARPA hosted in St. Louis.

To answer these question, the researchers worked with a 28-year-old man who is paralyzed. They impanted an electrode array in both his motor cortex and sensory cortex, the region of the brain that recognizes tactile sensations such as texture and pressure. Wires from the motor cortex array controlled the hand, as they did for the female volunteer, and sensors in the hand also conveyed information, via another set of wires, back to the electrode array in the sensory cortex.

The researches showed that this feedback system allowed the hand to communicated directly with the brain. A video included om Sanchez’s presentation, showed a researcher blindfolded the man and gently pressed on different fingertips in the prosthetic hand. The volunteer was able to identify which fingertip was being touched with “nearly 100% accuracy” even without seeing it, according to a press release by DARPA about the research.

People who have prosthetic hands today rely on being able to see what the hand is doig to control it, said Sliman Bensmaia, an associate professor of neuroscience at the University of Chicago. But people will never be able to use these hands with dexterity until they can feel what they are doing without looking at them, he said. Bensmaia did preliminary research for Sanchez’s team on how to make the electrode array work in the sensory cortex.

“On the short term, you want to know whether you are touching an objects, and how much pressure you are exerting on it, those basic things that you need to hold things,” Bensmaia said. He also added that as the technology progresses, touch sensory may also be able to convey temperature and texture.

Although the current demonstration is the first of a prosthetic hand directly communication with the brain, other researchers have demonstrated they they can relay information from sensors in the prosthetic hand to electrodes in the nerves in the arm than then communicate with the brain.

“(However), in situations where people have spinal cord injury, they are quadriplegic … you probably couldn’t give them sensation back through the nerves”, because the have lost the use of the nerves in their arm, said Dr. Paul S. Cederna, a professor of plastic surgery and biochemical engineering at the University of Michigan.
Devices on the market now rely on body power, where a healthy part of the body controls the prosthetic through cables and harnesses, or myoelectric devices that uses electrical signals from muscles attached to the prosthetic to control it.

Researches are working on developing highly sensitive prosthetic arms that can recreate nearly every motion of a real arm, and bionic hands than can be controlled through an iPhone.

The big benefit of Sanchez’s approach is being able to use prostheses for people with spinal cord injuries, Cederna said. The 28-year-old man in the current demonstration has been paralyzed for more than a decade because of a spinal cord injury.

Although Cederba was not involved in Sanchez’s research, he conducts DARPA-funded research on how to improve control of prosthetic device through peripheral nerves, such as those in the arm.

The idea of implanting an electrode array into the brain to either control or receive signals from a prosthetic limb is a big step forward, but there is still a ways to go. Cederna said, “The biggest challenge, once you put that electrode into the brain, you develop scarring around the electrode, and that makes it increasingly difficult to pick up the signals it needs to pick up”.

Researchers are working hard to develop electrode arrays that work for longer periods of time, Bensmaia said. He added that the current electrode arrays in the motor cortex only work for a few years, although the arrays in the sensory cortex appear to be more stable.