The mentality behind the famous proverb “seeing is believing” is helping some amputees find a new association with their artificial limbs. Researchers from Ecole Polytechnique fédérale de Lausanne (EPFL) made a way to defeat the “phantom limb” problem experienced by many amputees, facilitating their brains to recognize their prosthetics as part of their bodies.
According to the nonprofit group the Amputee Coalition, in the United States alone, nearly 2 million people have amputations. Some 185,000 amputations are performed every year in the U.S., and many of those limbs are substituted by prosthetics.
However, problems arise when an amputee’s prosthetic doesn’t connect with their brain’s perception of their missing limb. Many amputees still feel their lost arm in a sense, called a ghost or phantom limb, and those phantom limbs are often supposed by the brain to be smaller than the missing limb. And, even though a rapidly-advancing prosthetics industry, most prosthetic limbs are not armed to give any sense of touch back into a patient’s body. This means amputees have to constantly make sure their limb is working, how they need it to work — something they wouldn’t do if the limb were still present.
The EPFL team wanted to examine just how much an amputee “seeing” his or her limb affected the awareness of a prosthetic. Rather than trusting only on sight, however, the team united touch and sight.
“The brain repeatedly uses its senses to analyse what belongs to the body and what is foreign to the body. We showed exactly how touch and vision can be united to deceive the amputee’s brain into feeling what it sees, inducing personification of the prosthetic hand with an added effect that the phantom limb develops into the prosthetic one,” explained Giulio Rognini of EPFL’s Laboratory of Cognitive Neuroprosthetics supervised by Olaf Blanke, in an association with Silvestro Micera of EPFL and Scuola Superiore Sant’Anna in Italy.
In two-hand amputees, the researchers gave the experiment subjects tangible sensations at the tip of their phantom limbs by energising the nerves found in their base. The patients sported virtual reality goggles that displayed an index finger in their prosthetic limb. When the sensation was applied, the index of the finger shone in response.
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The patients stated they felt like the prosthetic hand belonged to their own body. At the end of the study, the amputees also said they felt like their phantom limb now fit the prosthetic. Before the experiment, the patients told researchers they felt like their ghost hands didn’t fit into the prosthetic. However, during the test, patients told a feeling that their phantom limb “stretched” into the prosthetic — letting it fit like a glove.
This is the first time multisensory data has been used to create convincing experiences in human subjects and gives researchers a better comprehension of a sensation known as “telescoping” which is when a phantom limb expands into a more ‘standard’ size.
This technology could give amputees a better association with their prosthetics while prosthetics continue to become more like limbs themselves.
“The setup is moveable and could one day be turned into a therapy to help patients embody their prosthetic limb permanently,” Rogini said.