The work was done in rhesus monkeys, who were given a local anesthetic to block nerve activity at the elbow, which caused temporary paralysis of the hand. Before they were given the anesthetic, though, the monkeys were trained to grasp a ball, lift it and release it into a tube. The signals from their brains to their hands and arms during these activities were recorded via an electrode implanted painlessly into their brains. After many repetitions, the researchers were able to see what kinds of signals were necessary to cause the the limbs to move. It turned out that the information was encoded in only about 100 neurons.
Knowing that, the scientists designed a device, called a multi-electrode array, that was able to pick up the tell-tale signals from the 100 or so neurons, decipher them and send them to the muscles -- bypassing the anesthetized nerves.
The signals that reached the muscles made them contract, enabling the monkeys to pick up the balls almost as well as they did before they were given the anesthetic.
The motions weren't perfect. Lee E. Miller, a professor in neuroscience at Northwestern and the lead investigator of the study said it might be because it takes some time for a monkey to learn how to use its arm again this way.
Read more at Discovery News
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