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Awakening Paralyzed Limbs
Brain signals can drive arm movement in a monkey with a paralyzed arm. "This is a big leap forward--they show the monkey using the ability to artificially contract his hand to actually pick up a ball," says Krishna Shenoy, a neuroscientist at Stanford University. "I think it's the first demonstration of a cortically controlled electrical stimulation system performing a task that would ultimately be useful for a human patient."
While spinal cord injury keeps the brain's electrical signals from reaching muscles, people paralyzed by these injuries often have intact nerves and muscles in their limbs. A technique called functional electrical stimulation (FES), in which implanted electrodes deliver electrical current to trigger muscle contractions, provides a way to reconnect this loop.
Devices that can restore hand function and bladder control to some paralyzed patients have already been approved by the U.S. Food and Drug Administration. Patients use residual muscle movement to consciously control these systems--a system that works well for some applications but limits the complexity of the movement that can be performed. For example, an FES device allows people to shrug a shoulder to trigger a grasping motion with their hand, but they cannot control how tightly to grasp.
Now, by pairing FES technology with brain implants, scientists are trying to create a more intuitive system for controlling paralyzed limbs, such that thinking about moving an arm or grasping with a hand would automatically be translated into the pattern of electrical activity needed to perform that movement. "It's much more natural, and if you can decode activity in enough muscles, you could move multiple joints simultaneously," says Robert Kirsch, a neuroscientist at Case Western Reserve University, in Cleveland, OH. Normal hand and arm motion involves fluid movement of multiple joints, rather than the limited movements possible today.
