A new study led by Paul Marasco, principal investigator, Advanced Platform Technology (APT) Centre, Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Ohio, suggests that targeted muscle reinnveration (TMR) drives a perceptual shift toward the amputee subjects’ adoption of their prosthesis as part of their body, rather than perceiving it as a tool.
To create that feeling of “embodiment,” researchers in Chicago led by Marasco designed a pressure-sensing system for the prostheses of two upper-limb amputees who had undergone TMR surgery. Each subject sat at a table, with the prosthetic arm left unattached but arranged in a natural position. As the subject watched, a researcher touched the prosthetic hand. Each time a sensor on the prosthetic hand detected a touch, it sent a signal to a small robot that poked a targeted area of the reinnervated skin. Also, when one of the subjects both saw and felt a touch on her prosthetic arm, the temperature of the arm just above the amputation site rose. This boost, Marasco said, may reflect the body adopting the prosthesis.
According to the study, which was published January 20, 2011, in Brain: A Journal of Neurology, seeing and feeling the touch at the same time created a powerful illusion in both amputees that the prosthetic hand was part of their body. When they saw but did not feel the researcher’s touch, the subjects didn’t feel a sense of ownership over the prosthetic, Marasco said. “It was really when the touch matched what they saw, that we saw these changes.”
In addition to this perceptual shift, the study authors concluded that TMR “may help to augment mechanisms of prosthetic motor control and function” and “may help amputees regain more intact self-images.”
Editor’s note: This story has been adapted from materials provided by Science News and Brain: A Journal of Neurology.
