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Claudia Mitchell uses her brain to directly control her artificial limb. ((CBC))

The first woman amputee to receive a thought-controlled prosthetic arm says it has revolutionized her life.

"Before the surgery, I doubted that I would ever be able to get my life back," said Claudia Mitchell. "But this arm and the Rehabilitation Institute of Chicago have allowed me to return to a life that is more rewarding and active than I ever could have imagined.

"I am happy, confident and independent."

Mitchell, a 26-year-old former marine from Ellicott City, Md., lost her left arm in a motorcycle accident in 2004. She appeared before military leaders in Washington, D.C., on Thursday along with doctors and anotheramputee to showcase the new prosthesis.

The new device is controlled by the user's brain and is meant to improve on earlier prosthetic arms byallowing more natural movements with agreater range of motion and restoring lost function.

A user just has to think about moving the arm to make it happen. When the user thinks "close hand," for example, electrical signals are sent through surgically rerouted nerves to make the motion happen.

Mitchell, 26, said her previous prosthetic arm was a source of frustration, but shecan use the new arm for tasks such as carrying a tray or opening a jar simply by thinking about it.

"This arm I can reach forward, I can reach up," Mitchell told a news conference. "You don't think it's very exciting to be able to reach up into a cabinet and get a big can of coffee now. Well, I think it's pretty exciting to be able to get it from there. This arm will someday offer the opportunity to be able to do that."

Refinements planned

Jesse Sullivan, 59, a double amputee, was the first man to receiveoneof theprosthetic arms five years ago. Heput the experimental device through its paces at the encouragement of researchers who wanted to refine it.

"When I left, they said, 'Don't bring it back looking new,' " Sullivan said with a grin.

Both of his arms were amputated after he suffered severe electrical burns while working as a utility linesman in 2001. He uses one bionic arm, and one standard prosthesis.

To make the new arms work, Mitchell, Sullivan and four other patients underwent a procedure called "muscle re-innervation," in which shoulder nerves that originally went to the amputated arm are grafted to chest muscles.

Thought impulses are received by the graft, muscle activity is picked up by electrodes that send signals to the arm's computer and then the arm's six motors cause the required movements.

About five months after the surgery, Sullivan was able to activate four different areas of his major pectoral muscle. A contraction in each area leads toa different action, such as opening and closing a hand.

A natural arm is able to make 22 discrete movements, said Gregory Clark, a professor of bioengineering and a prosthetics researcher at the University of Utah.

Both Mitchell and Sullivan said they hope amputees returning from war will be able to benefit from the research by the U.S. National Institutes of Health and the military's Defence Advanced Research Project Agency.

With files from the Associated Press