Researchers at Case Western Reserve University, Cleveland, OH, and the Louis Stokes Cleveland Veterans Affairs Medical Center have discovered that patterns of electric signals sent by a computer into nerves in a patient’s arm and to his brain, can give distinct sensations of touch to the patient’s prosthetic limb. They can even differentiate what is touching the limb, as well as more than a dozen distinct points and locations.
Working with two patients, the researchers also found another unexpected outcome—that phantom pain also disappeared. Despite having initial phantom pain, both men said that the first time they were connected to the system and received the electrical stimulation, was the first time they'd felt their hands since their accidents. In the ensuing months, they began feeling sensations that were familiar and were able to control their prosthetic hands with better dexterity.
When they began the study, the first sensation the users felt was merely a tingle. Later, to provide more natural sensations, the research team developed algorithms that convert the input from sensors taped to a patient’s hand into varying patterns and intensities of electrical signals. The sensors detect only pressure. But, the different signal patterns, passed through the cuffs, are read as different stimuli by the brain.
Different signal patterns interpreted as sandpaper, a smooth surface, and a ridged surface enabled a blindfolded patient 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.
In addition to hand prosthetics, the researchers believe the technology can be used to help those using prosthetic legs receive input from the ground and adjust to gravel or uneven surfaces. Beyond that, the neural interfacing and new stimulation techniques may be useful in controlling tremors, deep brain stimulation and more.