Schwartz and colleagues report that the monkeys learned quickly and were soon able to operate the arm almost as if it was a natural appendage, avoiding obstacles and changing trajectory when scientists surprised them by moving the target food.
The research appears in the current issue of Nature.
Mind Over Matter
The new work is one of many widespread efforts to develop brain-machine interface (BMI) technology, which could someday help people with spinal cord injuries, strokes, and degenerative neuromuscular diseases such as Lou Gehrig's disease.
(Related: "Thought-Controlled Machines May Be One Step Closer" [April 12, 2005].)
"It represents the current state of the art in the development of neuroprosthetic controllers for complex arm-like robots," wrote physiologist John Kalaska of the Université de Montréal.
Kalaska was unaffiliated with the study but penned a commentary on the work for Nature.
"The ability to tap into discrete cortical regions with only a few electrodes and development of simple algorithms for near real-time control considerably enhances the potential for development of practical neural-enabled motor prostheses," added Ranu Jung, a biomedical engineer with Arizona State University.
"The work presented is an exciting step towards making this a reality."
While the concept of brain-operated prosthetics is promising, though, some major challenges remain before the devices become practical, Kalaska said.
Durable sensor electrodes must be developed, because current systems degrade quickly. Today's lab settings also feature an array of bulky computer systems that must somehow be condensed to a much more manageable size.
Kalaska also stressed that human brains must receive information from prosthetics as well as send it.
Sensory receptors in real skin or muscles, for example, report back to the brain so that a hand doesn't squeeze too hard or let objects fall.
Current robotic appendages lack this feedback element, which is essential to giving the devices a natural feel.
Krishna Shenoy, a Stanford University neuroscientist unaffiliated with the research, said the new work provides a valuable real-world addition to past studies in which monkeys have controlled virtual reality cursors on computer screens.
"This is a very powerful first demonstration of direct brain control of a real prosthetic arm," he said. "This is the first time a monkey has directly seen a real arm, controlled it in three dimensions, and grasped objects to feed himself.
"I think it's a major advance because, in some loose way perhaps, he's adopted that arm. He's able to see that arm but not be bothered by the fact that it's not truly his and still act upon the world with it."
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