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Scientists had put a probe in the animals' brains that monitored how often a single brain cell was firing electrical signals. Once the wrists were paralyzed, that firing rate was converted into an electrical stimulation that went to the wrist muscles.
Different firing rates made the hand press downward or upward, or relax. The monkeys quickly learned to use the brain cells to control their wrist muscles and continue playing the computer game.
In people, more complex movements would require monitoring many brain cells at once to activate multiple muscles, Moritz said. Researchers would rely on the brain to learn how to coordinate all these signals to produce a useful motion, he said. After all, that's what the brain does when a person learns to swing a tennis racket effectively, he said.
"There's a long ways to go, and there's no way to say with confidence that it will work," Moritz said.
It's also possible that a single brain cell could stimulate a group of muscles, if its signals are relayed to particular sites in the spinal cord, researchers said.
Andrew Schwartz of the University of Pittsburgh, who has used brain signals to enable monkeys to control robot arms, said he considered the new work a modest advance, noting hurdles that remain.
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