A team of scientists has developed a technology that simulates tactile sensation in people without sensitivity in their hands. The technology, which uses brain stimulation connected to a prosthetic hand attached to a chair, is the closest thing to “real” touch yet achieved.
The researchers, who are part of the American group Cortical Bionics Research Group, have developed a method to encode tactile sensations of the hand through specific microstimulation patterns on implantable electrodes in the brain. This allows people with spinal cord injuries to not only control a bionic arm with their brain, but also feel edges, shapes, curvatures and tactile movements, something that until now was not possible.
“In this work, for the first time in research we have gone further into the field of brain-computer interfaces: we transmit tactile sensations related to orientation, curvature, movement and three-dimensional shapes to a participant using a brain-controlled bionic limb“advances Giacomo Valle, from Chalmers University of Technology, Sweden, and lead author of the study.
The sense of touch provides amazing information to our daily lives. If we use gloves, we will realize that by dampening the sense of touch, many tasks become frustrating and complex. “If you can’t feel, you have to constantly watch your hand while doing anything, and you still run the risk of spilling, crushing or dropping objects,” explains Charles Greenspon, a neuroscientist at the University of Chicago and co-author of the research.
In people with spinal cord injury, the electrical signals that go hand in hand with tactile information to the brain are blocked. A bionic hand or a brain-controlled prosthesis can restore some functionality to the limb but without the sense of touch.
Objective: improve sensitivity
The team’s goal was improve usability of a bionic limb installed in a wheelchair or similar equipment close to the user, and they have succeeded. The results were published this Thursday in the magazines Nature Biomedical Engineering and Science.
The new studies are the result of years of collaboration between scientists and engineers from the universities of Chicago, Pittsburgh, Northwestern, Case Western Reserve University and Blackrock Neurotech. In the first study, published in Nature Biomedical EngineeringGreenspon and his colleagues focused on ensuring that electrically evoked tactile sensations were stable, precisely located and of sufficient strength to be useful in everyday tasks.
The researchers created detailed “maps” of the brain areas that corresponded to specific parts of the hand using brief impulses on electrodes. Participants had to report where and with what intensity they perceived each sensation. The team found that when two electrodes in close proximity are stimulated together, participants they felt a stronger and clearer touch. They also performed extensive testing to confirm that the same electrode consistently creates a sensation corresponding to a specific location, just as a natural limb would.
Intuitive touch
The article of Science went a step further to make artificial touch even more immersive and intuitive. The project was led by Giacomo Valle, who was at the University of Chicago at the time.
“Two electrodes close together in the brain do not create sensations that ‘padding’ the hand into small, ordered patches with one-to-one correspondence, but instead sensory locations overlap“explains Greenspon, who shares the main authorship of this work with Sliman Bensmaia, from the University of Chicago, who died suddenly in 2023.
The researchers decided to test whether they could use this overlapping nature to create sensations that would allow users to feel the boundaries of an object or the movement of something sliding across their skin. After identifying pairs or groups of electrodes whose “touch zones” overlapped, the scientists activated them in carefully orchestrated patterns to generate sensations that progress through the sensory map.
surprising result
The result was surprising: participants described the sensation of a soft, gliding touch that passed gently over their fingers, which scientists attribute to the extraordinary brain capacity to unite sensory inputs and interpret them as coherent experiences.
Sequential activation of the electrodes also significantly improved the participants’ ability to distinguish tactile shapes complex and respond to changes in the objects they touched. They could sometimes identify letters of the alphabet written electrically on their fingertips, and could use a bionic arm to grip a steering wheel when it began to slip through their hand.
The team hopes that as they continue to improve electrode design and surgical methods, the coverage of the hand will become even thinner and allow for a more realistic response. The method is also promising for people with other types of sensory losslike it can restore the sense of touch after a mastectomy. Although there are still many challenges to overcome, the path to recovering touch seems increasingly clear.
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