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by neuroscientist Miguel Nicolelis at Duke University used the brain of a living monkey to control a robotic arm.The researchers implanted an array of fine wire electrodes in the brains of two owl monkeys. First they used the array to record neural patterns as they trained the mon- keys to use their hands for specific tasks, such as reaching for food. These patterns gave enough information to predict where a monkeys arm would be, milliseconds after the monkeys brain produced the signal.The scientists used the data derived in this way to write a con- trol program for robotic arms physically separate from the monkey. One arm, located in the same laboratory, was directly connected to the brain: a second one, distantly located in a laboratory at MIT, was connected via the Internet. For each arm, as the monkey moved its natural arm, the artificial limb faithfully followed its movements.

This astonishing result is not the final answer to the problem of giving a paralyzed person a useful BMI, which ideally should tap neural signals without any need for bodily motion. In 2003, Nicolelis and his group reported achieving that goal, although in monkeys, not humans. The scientists implanted electrodes in the brains of two macaque monkeys and recorded the neural patterns that arose as the animals learned to work a joystick that controlled a computer cursor; the monkeys were rewarded with a drink of juice when they used the cursor to reach and virtually grasp a target on the computer screen. Then the researchers disconnected the joystick but continued to tap the neural signals. Baffled at first, the monkeys soon realized that al- though manipulating the joystick no longer did anything, they could guide the cursor merely by thinking about it, with no muscular ac- tion. In a final step, the signals from the brain were rerouted to control a robot arm rather than the cursor. By the end of training,says Nicolelis,I would say that these monkeys sensed they were reaching and grasping with their own arms instead of the robot arm.

The ultimate goal is to develop similar brainmachine interfaces for humans.As an important step toward that goal, the Atlanta-based researcher and neurologist Philip Kennedy has, for the first time, en- abled a human brain to control an external device with no associated bodily action. Kennedy implanted electrodes into the brain of a para-

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