US scientists have in a breakthrough research found that realistic sensations of touch can be restored in human amputees by directly stimulating the nervous system.
In the study, neuroscientists from the University of Chicago used neuroprosthetic devices to turn the pressure "felt" by a prosthetic hand into a signal that feeds directly into the parts of the brain that deal with hand movement and touch.
"If you want to create a dexterous hand for use in an amputee or a quadriplegic patient, you need to not only be able to move it, but have sensory feedback from it," said Sliman Bensmaia, Associate Professor at the University of Chicago.
"The idea is that if we can reproduce natural-feeling sensations exactly, the amputee won't have to think about it, he can just interact with objects naturally and automatically," Bensmaia added.
The team worked with two male subjects who each lost an arm after traumatic injuries.
Both subjects were implanted with neural interfaces, devices embedded with electrodes that were attached to the median, ulnar and radial nerves of the arm.
Those are the same nerves that would carry signals from the hand were still intact, the researchers said.
The results showed that a single feature of electrical stimulation -- dubbed the activation charge rate -- can determine the strength of the sensation -- such as intensity discrimination, magnitude scaling, and intensity matching.
By changing the activation charge rate, the team could change sensory magnitude in a highly predictable way.
By modulating the number of nerve fibres stimulated and the frequency of stimulation, sensory information could be transmitted such that the amputees could distinguish distinct levels of tactile intensity, that is, the difference between a seven and a 10 on a scale of intensity.
However, these artificial touch will only be as good as the devices providing input, the researchers stated.
The study was published in the journal Science Translational Medicine.
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