(CNN) -- Scientists have trained a group of monkeys to feed themselves marshmallows using a robot arm controlled by sensors implanted in their brains, a feat that could one day help paralyzed people operate prosthetic limbs on their own, according to a study out Thursday.Lead researcher Andrew Schwartz of the University of Pittsburgh said he believes it won't be long before the technology is tested in humans, although he predicts it will be longer before the devices are used in actual patients with disabilities.

"I think we'll be doing this on an experimental basis in two years," said Schwartz, professor of neurobiology at the university's School of Medicine.

The results were appeared in the journal Nature's online edition on Thursday. The arm is controlled by a network of tiny electrodes called a brain-machine interface, implanted into the motor cortex of the monkeys' brains -- the region that controls movement.

It picks up the signals of brain cells as they generate commands to move and converts those into directional signals for the robotic arm, which the monkeys eventually used as a surrogate for their own.

The researchers report that one monkey achieved a success rate of 78 percent over 13 days of trials, while a second monkey completed its tasks with the arm in 61 percent of tests conducted over two days. They said the animals also were able to direct the arm around obstacles to ensure safe delivery of the food, which included small items such as grapes and marshmallows.

The ability of the monkeys to interact with the robotic arm and objects in the work space embodies a "multi-degree-of-freedom" that "paves the way towards the development of dexterous prosthetic devices that could ultimately achieve arm and hand function at a near natural level," according to the Nature article.

"I'm most excited by the chance to study many neurons at the same time, so we can see how they work together as a network," Schwartz told CNN. The research provides the opportunity to consider interactions among neurons, he added. "Understanding the brain at a more fundamental level, I think, will result in all sorts of chances to treat a wide range of brain diseases such as Parkinson's and Alzheimer's", according to the professor.

The researchers initially trained two monkeys to use a joystick to manipulate the arm. Then, the monkeys' arms were restrained by placing them in tubes, and the robotic arm was switched over to brain control so the monkeys could translate their wishes into commands.

In a video, a macaque monkey uses the robotic arm to seize pieces of marshmallow off a thin rod positioned at various locations. The arm is designed to move realistically, with a range of shoulder movements -- an elbow that moves in just one direction and a simple claw grip to simulate a hand.

Brain interfaces are not particularly new -- human versions have been around for several years. But this is the first time a brain-machine interface has been used to fulfill a useful function, such as allowing monkeys to feed themselves.

"Up until now, almost all demonstrations (of the technology) have been in a virtual world," Schwartz said. Successfully developing these brain implants for humans will require more resilient, long-lasting electrodes.

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