A study by neuroscientists at the University of Chicago shows how people with amputations can learn to control a robotic arm through electrodes implanted in their brains. The research, published online November 27 in Nature Communications, details changes that take place in both sides of the brain used to control the limb that has been amputated and the remaining, intact limb. The results show both areas can create new connections to learn how to control the device, even several years after the amputation has occurred. Previous experiments have shown how paralyzed human patients can move robotic limbs with a brain-machine interface (BMI); this study is one of the first to test the viability of these devices in people who have amputations.
“That’s the novel aspect to this study, seeing that chronic, long-term amputees can learn to control a robotic limb,” said Nicho Hatsopoulos, PhD, professor of organismal biology and anatomy at UChicago and senior author of the study. “But what was also interesting was the brain’s plasticity over long-term exposure, and seeing what happened to the connectivity of the network as they learned to control the device.”
Monkeys were trained to use their thoughts to move a robotic arm and grasp a ball.
Photograph Courtesy of Nicho Hatsopoulos, Karthikeyan Balasubramanian, University of Chicago.
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During the study, researchers worked with three rhesus monkeys who suffered injuries at a young age, four, nine, and ten years ago, and had to have an arm amputated to rescue them. (Their limbs were not amputated for the purposes of the study.) Researchers implanted electrode arrays in the side of the brain opposite, or contralateral, to the amputated limb in two of the monkeys, the side used to control the limb that was amputated. In the third monkey, electrodes were implanted on the same side, or ipsilateral, to the amputated limb, the side that still controlled the intact limb.
The monkeys were then trained to move a robotic arm and grasp a ball using only their thoughts. During the study, scientists recorded the activity of neurons where the electrodes were placed, and used a statistical model to calculate how the neurons were connected to each other before the experiments, during training, and once the monkeys mastered the activity. The connections between neurons on the contralateral side—the side that controlled the amputated arm—were sparse before the training, most likely because they had not been used for that function in some time, according to the researchers. The study found that as training progressed, these connections became more robust and dense in areas used for reaching and grasping.
On the ipsilateral side, the connections were dense at the beginning of the experiments, but as training progressed, researchers found that the connections were pruned and the networks thinned, before rebuilding into a new, dense network.
“That means connections were shedding off as the animal was trying to learn a new task, because there is already a network controlling some other behavior,” said Karthikeyan Balasubramanian, PhD, a postdoctoral researcher who led the study. “After a few days it started rebuilding into a new network that can control both the intact limb and the neuroprosthetic.”
Editor’s Note: This story was adapted by materials provided by University of Chicago Medical Center.
