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The artificial hand that amputees feel is their own

OneStepCloser

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The artificial hand that amputees feel is their own


Electrodes implanted around nerves enable amputees to control gentleness of touch

PUBLISHED : Thursday, 09 October, 2014, 10:05pm
UPDATED : Thursday, 09 October, 2014, 10:05pm

Associated Press in Washington

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The robotic arm picks up a tomato without squishing it.

Scientists are moving closer to an artificial hand that can feel: Implanted electrodes have allowed some amputees to tell by touch how gently to grasp, letting them pluck fruit without crushing it.

Two amputees told researchers at Case Western Reserve University that when some of their remaining nerves were wired to a robotic arm they felt more like they were grasping objects with their own hand than with a tool.

"This feels like normal sensation," one of the men, Igor Spetic, said.

When researchers touched different spots on his artificial hand, "sometimes it felt like a cotton ball", he said. "Sometimes like sandpaper."

An unexpected benefit: The phantom pain both men had felt since losing their limbs in industrial accidents had nearly disappeared since they began the experiment, the researchers reported on Wednesday in the journal Science Translational Medicine.

It will take years of additional research before robotic hands really let people feel what they touch. But the new research was an important step, said Dr Michael Boninger, who directs the University of Pittsburgh Medical Centre's rehabilitation institute.

Beyond better function, getting feedback from the limb "would be a spectacular thing to be able to have, that you feel like the arm is your own", he said.

People with natural limbs take for granted the intuitive control that a sense of touch allows. Reach for something and your hand naturally grasps with just enough force. But users of prosthetic hands have to watch carefully every motion, judging by eye how tightly to squeeze so they do not either drop something or crush it. Consequently, many amputees abandon prosthetic hands, or do not use them as much as they would like.

Here is how it works: The team at Case Western and the Cleveland Veterans Affairs Medical Centre implanted electrodes around three nerves in the stump of the men's arms.

Wires snake from under the skin. During monthly visits to a lab, scientists hook the men up to a machine that sends electrical signals between the stump and a prosthetic hand. Sensors on the hand can convey a sense of touch from 16 to 19 spots.

At first, it just felt like electrical tingles, Spetic said.

But as researchers adjusted the pattern and intensity of those signals, he started to feel pressure in his missing fingers, and even different textures.

The real test was when the men tried plucking grapes and cherries from their stems. Blindfolded, they crushed a lot of fruit until the sensory feedback was switched on and they could control the gentleness of their grasp.

"We can change what they're feeling and how they're feeling it," said Case Western biomedical engineer Dustin Tyler.

It was working by reactivating dormant areas of the brain that produced the sense of touch for that hand, he said.

What explains the disappearance of that phantom pain that Spetic said was like a vice gripping his missing fist? Tyler said researchers did not know but it may be that making the brain sense a hand was there again, rather than missing, could affect how it interprets pain signals.

The under-the-skin electrodes are still working up to two years after they were implanted. Tyler hopes to begin experiments outside the laboratory soon.

 
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