Growing advent of futuristic development of realistic prosthetic/ robotic devices has shown that even after a full year, the bionic touch did not remap the brain in people whose amputated limbs were replaced with prosthetic limbs. The location of the touch sensors on the prosthetic devices and the participants' subjective sensation revealed no match, as per the neuroscientists at the University of Chicago and Chalmers University of Technology, published in the journal Cell Reports.
The limitation of the nervous system to adapt to different sensory input attributes to the stability of its touch sensations. Development of prosthetic limbs requires qualities of not only being able to be operated with a user's own neural activity, but can to accurately and precisely receive and relay sensory information to the user.
"One problem with current neural electrodes is that you can't tell during the implantation surgery which part of the nerve corresponds to what sensation, so the electrodes don't always land in exactly the location in the nerve that would match the location of the sensors in the prosthetic hand," says lead author and developer of the neuromusculoskeletal prostheses, Max Ortiz Catalan.
The study enrolled three participants with above-elbow amputation. They were equipped with high-tech neuroprosthetic devices that were affixed directly to their humerus bone - upper arm bone. One set of electrodes implanted in the residual arm muscles helped the users to control the signals from the prosthetic devices whereas another set of implanted electrodes received sensory feedback.
It was observed among the prosthetic users that despite being able to observe their hand while interacting with objects, they were not able to report the feeling of sensation on the thumb (where was originally felt), but rather in other hand locations, such as their middle finger or the palm.
"Every day, for a year, these subjects saw their prosthetic thumb touching things and felt it in a different location - sometimes close to the thumb, but not on it - and the sensation never budged. Not even a smidge," said senior author Sliman Bensmaia from UChicago.
The study thereby emphasizes the importance of knowing exactly where to place electrodes when implanting sensory arrays for patients using these types of neuroprosthetic devices, as it appears unlikely that the brain is capable of making substantial adjustments in how it perceives that sensory input.