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Giving life to limbs Prostheses aim to provide amputees with a sense of touch

In an underground laboratory at the University of Chicago, neuroscientist Sliman Bensmaia peered at a blue computer monitor attached by wires to a rhesus monkey's brain.

A lab technician grazed the animal's finger using a metal probe, and the computer screen erupted in red.

"That's pretty cool," said Bensmaia, grinning. "You can see the brain becoming active just by tapping the hand."

Next, instead of physically tapping the animal's hand, the technician planned to run a small current of electricity through electrodes in the animal's brain to simulate the probe. If the animal looked in a certain direction, the scientists would know the "virtual touch" worked.

This research is part of a groundbreaking quest to accomplish what was once the stuff of science fiction -- build a machine that helps humans to feel.

Funded by the Defense Advanced Research Projects Agency (DARPA), and spurred by the return of injured Iraq and Afghanistan war veterans, these researchers aim to design prostheses that will not only be able to move, but will also provide amputees and quadriplegics with a sense of touch.

Scientists have known for more than a century that applying electricity to neurons can elicit certain reactions -- a muscle twitch, a sudden feeling of euphoria, a long forgotten memory recalled. But stimulating those cells to help people overcome certain disabilities has only been done more recently, spearheaded in the 1960s by the development of the cochlear implant for hearing.

Unlike hearing or vision, however, touch research languished for decades, hobbled by the expensive machinery needed to perform experiments, Bensmaia said.

"People take [their sense of touch] for granted more than vision or hearing," he said.

But then hundreds of wounded veterans began returning home without arms or legs or the use of their limbs due to spinal cord injuries, and interest in developing better prostheses spiked. Through the DARPA project, scientists at Johns Hopkins University Applied Physics Laboratory last year completed a new prosthetic arm, which can rotate, twist and bend in 26 different ways. Scientists also recently outfitted patients with brain electrodes that allowed them to move simpler robotic arms with their thoughts.

Without any tactile feedback, however, the usefulness of the prostheses is limited. Lacking the sense of touch, patients could not, for example, differentiate between corduroy and silk, a pen and a pencil or a poke and a punch. More importantly, "they have to constantly be visually monitoring what they are doing or they wouldn't know whether they were holding or crushing something," Bensmaia said.

So last year, Johns Hopkins gave Bensmaia's lab about $1.5 million of its federal money to develop even more advanced prostheses that will eventually give the users a simulated sense of touch through the machine's metal and motors.

The U of C scientists set out to identify and replicate the qualities of touch, including texture, shape and force, through algorithms. They implanted platinum alloy electrode arrays, each the size of a pencil eraser, into the Rhesus monkeys' brains. The scientists then created neural impulses by emitting small, but focused, electrical currents, and recorded the animal's behavior in response.

After simulating thousands of different touch sensations, Bensmaia and his team hope to build algorithms, essentially mapping out the way the brain reads those touches. They will then use those sensory algorithms to build software for the robotic arm's computerized sensors that will transmit impulses to electrodes in the human brain, mimicking touch.

Josh Berg, Bensmaia's study director, grabbed his head between his hands and said, "Up here, we are not vision, touch or smell. We are all electricity. What we are trying to do is translate information into a language the brain can understand."

Johns Hopkins and its collaborators expect to implant electrodes in the first human patient this summer.

U of C neuroscientist Nicho Hatsopoulos recently applied to work on the development of that wireless system. Hatsopoulos, who specializes in the neuroscience of movement, co-founded Cyberkinetics Neurotechnology Systems, which was one of the first companies to implant electrodes in humans in order to control machines with their thoughts.

"Where we are right now is basically the beginning stages of the $6 million man," said Hatsopoulos, standing in his laboratory while a rhesus monkey moved a cursor around a computer using only his thoughts.