A new study provides hope for the approximately 5.4 million Americans living with paralysis.
In a scientific first, a team of researchers from the California Institute of Technology brought natural sensation back to a paralyzed man’s arm, using electrodes implanted in the brain. The approach is still in its early days, but senior study author Richard Andersen, a professor of neuroscience and the director of the T&C Chen Brain-Machine Interface Center at CalTech, says it could someday open the door to prosthetic limbs capable of feeling and sensing just like natural ones.
“We want them to not only have the visual feedback, but also the touch feedback,” Andersen says. “You can of course grab something based on vision, but once you try to pick it up and manipulate it, it’s very hard to do without touch and body position. It’s a little like when you go to the dentist and have your gums numbed: It’s hard to talk.”
The approach used in the new study, however, could make for prostheses that get around those roadblocks. A paper describing the results was published Tuesday in the journal eLife.
The CalTech team tested its method in a 32-year-old man who became paralyzed from the shoulders down after a spinal injury. Ninety-six tiny electrodes were surgically implanted in the part of his brain that controls bodily sensation.
The researchers tested the electrodes’ function by sending electrical currents through each one at a range of amplitudes. As they did, the patient sat in a wheelchair facing a television screen. After each electrode fired, a purple circle appeared on the screen, indicating that an electrode was active. The circle was followed by an auditory cue prompting the man to describe what sensation he felt, if any. In a second experiment, the researchers isolated the five most promising electrodes — those that had reliably achieved the same result over a period of weeks — and repeated the procedure.
Throughout the course of the trial, the man reported feeling a slew of different natural sensations, some related to the body moving through space and some related to feelings on the skin. He described everything from goosebumps and pinches to forward and upward movement — a range of results that’s never been achieved before, Andersen says.
“We could, at some locations, switch between a sense of touch and a sense of position, so that means we can begin to explore producing a more complicated sense of sensation,” he explains. “Next, we’ll attempt to demonstrate whether the stimulation actually helps in the brain control of a prosthetic limb.”
Other teams, like one at the University of Pittsburgh, have done similar work, Andersen says, but have mostly achieved sensations like buzzing or tingling, rather than the range of natural feelings seen in the new study. Andersen says he’s not totally sure why his lab succeeded where others were stymied, but says it likely has to do with either the placement of the electrodes or the specific way they were used to stimulate the brain. Whatever the secret, Andersen says the results are encouraging and worthy of further study.
“It’s pretty exciting for the patient to be able to feel again,” Andersen says. “We hope also that it will provide a sense of embodiment [for patients with prostheses], so they feel like, after a while, the prosthetic limb becomes part of their body.”