20 October 2008—For years, doctors have treated patients suffering from life-threatening heart blockages by adding new blood vessels that reroute blood around arterial traffic snarls. Researchers have been working on methods for doing an electronic bypass around a damaged spine with the aim of restoring movement to paralyzed limbs.
Though it will be years before spinal bypass surgery reaches even the clinical-experiment stage, researchers at the University of Washington (UW) and the Washington National Primate Research Center, both in Seattle, have figured out a way to get macaque monkeys in their lab to manipulate temporarily paralyzed muscles in their arms using brain-controlled electrical stimulation. In research reported last week in Nature , they describe what happened when they attached electrodes to neurons in a monkey’s motor cortex—the part of the brain that controls voluntary movement—and used fairly simple algorithms to translate activity in these cortical cells into electrical signals that tell muscles when, how much, and how forcefully to contract.
In exchange for a reward of applesauce, the monkeys had been conditioned to create just the right amount of torque in their wrists to move a cursor on a display so that it hit a target. To conduct the experiments, the researchers used anesthesia to block signals in a nerve just below the shoulder of a monkey’s arm, temporarily paralyzing the rest of the limb. The brain cells that control wrist movement were still firing in response to the monkey’s desire to hit the target and get the payoff, but with the neural connection shut down, the wrist remained limp. The scientists implanted electrodes into the monkey’s motor cortex and fed the electrical signals they received from the monkey’s brain into a computer. The computer then translated the signals into a stimulating current that was fed to electrodes implanted below the nerve block in the monkey’s wrist. The monkeys were able to learn to manipulate their own brains to get their wrists moving.