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October 12, 2014 AT 1:00 am

New Prosthetic System Allows Amputees to Discern Familiar Sensations

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Medical researchers have developed a new system to help restore the sense of touch in amputees which they hope to make available for home use within five years time. From ScienceDaily:

“The sense of touch actually gets better,” said Keith Vonderhuevel, of Sidney, Ohio, who lost his hand in 2005 and had the system implanted in January 2013. “They change things on the computer to change the sensation.”
“One time,” he said, “it felt like water running across the back of my hand.”
The system, which is limited to the lab at this point, uses electrical stimulation to give the sense of feeling. But there are key differences from other reported efforts.
First, the nerves that used to relay the sense of touch to the brain are stimulated by contact points on cuffs that encircle major nerve bundles in the arm, not by electrodes inserted through the protective nerve membranes.
Surgeons Michael W Keith, MD and J. Robert Anderson, MD, from Case Western Reserve School of Medicine and Cleveland VA, implanted three electrode cuffs in Spetic’s forearm, enabling him to feel 19 distinct points; and two cuffs in Vonderhuevel’s upper arm, enabling him to feel 16 distinct locations.
Second, when they began the study, the sensation Spetic felt when a sensor was touched was a tingle. To provide more natural sensations, the research team has developed algorithms that convert the input from sensors taped to a patient’s hand into varying patterns and intensities of electrical signals. The sensors themselves aren’t sophisticated enough to discern textures, they detect only pressure.
The different signal patterns, passed through the cuffs, are read as different stimuli by the brain. The scientists continue to fine-tune the patterns, and Spetic and Vonderhuevel appear to be becoming more attuned to them.
Third, the system has worked for 2 ½ years in Spetic and 1½ in Vonderhueval. Other research has reported sensation lasting one month and, in some cases, the ability to feel began to fade over weeks.
A blindfolded Vonderhuevel has held grapes or cherries in his prosthetic hand — the signals enabling him to gauge how tightly he’s squeezing — and pulled out the stems.
“When the sensation’s on, it’s not too hard,” he said. “When it’s off, you make a lot of grape juice.”
Different signal patterns interpreted as sandpaper, a smooth surface and a ridged surface enabled a blindfolded Spetic to discern each as they were applied to his hand. And when researchers touched two different locations with two different textures at the same time, he could discern the type and location of each.
Tyler believes that everyone creates a map of sensations from their life history that enables them to correlate an input to a given sensation.
“I don’t presume the stimuli we’re giving is hitting the spots on the map exactly, but they’re familiar enough that the brain identifies what it is,” he said.

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