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Monkeys' Brains Operate Robotic Arm

Brian Handwerk
for National Geographic News
May 28, 2008
 
In a mental meeting of monkey and machine, two primates have learned to feed themselves with a robotic arm by controlling the appendage with signals from their brains.

The success boosts hopes for mind-controlled robotic prosthetics that may help disabled humans achieve some mobility.

The experiment employed "visualization" methods of learning that study leader Andrew Schwartz likens to those employed by many professional athletes.

"You show the animal what you want him to do, and neurons in the brain go off as if he were actually doing it," said Schwartz, a neurobiologist at the University of Pittsburgh School of Medicine.

Mapping that brain activity enabled Schwartz and colleagues to figure out what nerve cell activity produced the desired physical actions.

Recording the Brain

Probes the width of a human hair were inserted into the neuronal pathways of the monkeys' motor cortex—a brain region that controls voluntary muscle movement.

Physical movement begins as electrical impulses generated by the activity of thousands of nerve cells.

When a monkey envisioned moving the arm, probes captured the neural activity and sent the information to a computer, which mapped that data to specific physical motions. (Related: "'Brain Reading' Device Can Predict What People See [March 5, 2008].)

Because brain activity is so complex, it is impossible to map the activity of all the neurons associated with motion. But the team developed an algorithm that was able to simulate and recreate much of the activity from the limited data detected by the probes.

This neuron-activity blueprint was then delivered to the robotic arm, which features working shoulder and elbow joints and a clawlike "hand."

Monkeys were able operate the arm merely by thinking. The animals fed themselves meals of marshmallows and fruit even when their real arms were restrained.

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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