Researchers add sense of touch to brain-controlled prosthetic limb
Researchers at the University of Pittsburgh, the University of Pittsburgh Medical Center, and other centers and institutions have discovered a way to endow brain-controlled prosthetic limbs with a sense of touch. In a paper to be published October 19 in Science Translational Medicine, they write, “Intracortical microstimulation of the somatosensory cortex offers the potential for creating a sensory neuroprosthesis to restore tactile sensation…. We show that microstimulation within the hand area of the somatosensory cortex of a person with long-term spinal cord injury evokes tactile sensations perceived as originating from locations on the hand and that cortical stimulation sites are organized according to expected somatotopic principles.”
John Hamilton at NPR writes that the researchers have applied their microstimulation technique to the benefit of Nathan Copeland, who twelve years ago lost the ability to control his fingers or sense what they were touching when a spinal cord injury disconnected his hand from his brain. Hamilton writes that the researchers “…gave Copeland a new way to reach out and feel the world around him…” via “…a mind-controlled robotic arm that has pressure sensors in each fingertip that send signals directly to Copeland’s brain.”
Copeland has described some of the sensations as electrical although many feel “natural.” Hamilton quotes researcher Robert Gaunt, a bioengineer and assistant professor in the Department of Physical Medicine & Rehabilitation at the University of Pittsburgh, as saying, “…we’re really not at the point where we could, say, get him to feel the difference between silk and burlap.”
The sensory capability adds a key feature to thought-controlled robotic arms, whose users had relied on visual feedback alone to see what the arms were doing. Hamilton quotes Mike McLoughlin, an engineer at the Johns Hopkins University Applied Physics Laboratory, as saying lack of tactile feedback makes it difficult to grasp a foam coffee cup without crushing it. McLoughlin is part of a team that built the limb that Copeland is using.
Hamilton reports that the researchers use a technique called magnetoencephalography. Gaunt explains, “We were able to see the parts of his brain that became active when he was watching videos of a hand being touched.” They then placed electrodes in Copeland’s brain that could stimulate the areas corresponding to each finger.
Amy Ellis Nutt in The Washington Post elaborates on how this works. “Last spring, the surgeons implanted four tiny electrodes in the left hemisphere of his brain, into the sensory cortex area that senses touch in the body’s right hand and fingers,” she writes. “Copeland already had chips implanted in his brain that connect him to a mind-controlled robotic arm. To test whether the new chips could allow him to experience touch, he was blindfolded so that he couldn’t see what the researcher was doing. One by one, the researcher touched each of the fingers on the robot’s right hand, and each time Copeland correctly identified the location of the touch.”
Nutt cites Gaunt as saying the project involved collaboration with multiple institutions and researchers. She writes, “The microelectrode package and control system were developed by Blackrock Microsystems….” The paper lists 10 authors representing nine departments and institutions.
Nutt adds, “The experiment with Copeland was a featured stop Thursday when President Obama visited Pittsburgh for a White House Frontiers Conference on advances in science, medicine and technology….
“’It’s amazing. Pretty cool,’ Obama said, before asking Copeland to ‘blow it up’ with a handshake, where they each pulled their hand away at the end. ‘I couldn’t be prouder of all of you.’”
