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Helping artificial limbs to feel real: Prosthetics with a 'sense of touch' more like part of body.

Rerouting nerves helped amputees view their artificial limbs more like body parts, a study to appear in Brain suggests. Such enhanced sense of ownership, scientists say, might lead to prosthetics that seamlessly replace a missing limb.

The new study was conducted with two amputees who had undergone a surgery called targeted reinnervation, in which the remaining nerve ends from their severed arms were rerouted to areas above the amputation site. These patches of skin served as proxies--touching different parts of the areas made the amputees feel as though distinct parts of their missing arms were being touched.

The research "tells us about the brain--that the brain can take this abnormal sensation and attribute it to the hand, to the arm," says neuroscientist Steven Hsiao of Johns Hopkins University in Baltimore, who wasn't involved in the work. "These people are feeling something. They feel like they're really touching something, presumably."

To create that feeling of limb ownership, or "embodiment," researchers led by Paul Marasco designed a pressuresensing system for prosthetics. Each time a sensor on a prosthetic hand detected a touch, it would send a signal to a small robot that would poke a targeted area of the reinnervated skin.

Using the robot system, Marasco and his team had each participant sit at a table, with the prosthetic arm unattached but arranged in a natural position. As the participant watched a researcher touch the prosthetic hand, the robot would simultaneously press on the reinnervated skin.

Seeing and feeling the touch at the same time created a powerful illusion in both amputees that the prosthetic hand was part of the body. When they saw but did not feel the researcher's touch, the participants didn't feel a sense of ownership over the prosthetic, says Marasco, now at the Advanced Platform Technology Center at the Veterans Affairs Medical Center in Cleveland. "It was really when the touch matched what they saw that we saw these changes."

Also, when one of the participants both saw and felt a touch on her prosthetic arm, the temperature of the arm just above the site of the amputation rose. This boost, Marasco says, may reflect the body adopting the prosthetic. When sensory information is blocked from a limb, such as an arm with nerve damage from a stroke, the limb's temperature drops slightly.

Although the new study is "a baby step," it's important, says bioengineer Michael Goldfarb of Vanderbilt University in Nashville. "What makes you feel something is a part of you is not just being able to move it." Sensory input can't be overlooked, he says, when creating good prosthetics.

"People feel like these are tools attached to their body. Even though they are very sophisticated, they are tools," Goldfarb says. "So the idea of trying to get sensory information back in would help integrate this limb as part of the body, help [people] control it and, one would argue, help them feel more whole."

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Title Annotation:Body & Brain
Author:Sanders, Laura
Publication:Science News
Geographic Code:1USA
Date:Feb 26, 2011
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