EPFL makes phantom members feel the heat
A device has been developed which allows amputees to experience temperature sensations and to reconnect to the part of the body they no longer have.
PostedMay 19, 2023, 6:36 p.m
The MiniTouch consists of a thin, portable sensor that can be placed on the finger of a prosthetic hand. It detects sensory information from the touched object, more specifically, the thermal conductivity of the object.
“When I touch the stump, I feel tingles in my missing hand, my phantom hand. But feeling a change in temperature is something else, something important… marvellous”, testifies Francesca Rossi.
Francesca Rossi is an amputee from Bologna, Italy. She recently participated in a study to test the effects of thermal sensory feedback to the skin of her residual arm. She is one of 17 people to have felt a change in temperature in her phantom hand, thanks to new technology from EPFL. But above all, she claims to feel reconnected with her missing member. “The thermal sensory feedback is a pleasant sensation, because you fully feel your phantom limb. You no longer feel it as a ghost, it is there again,” she continues.
The feeling is not on the place of contact
Researchers Silvestro Micera and Solaiman Shokur want to incorporate new sensory feedback into prostheses, to provide amputees with more realistic touch. Their latest study focuses on temperature. Unexpectedly, their discovery about sensory temperature feedback exceeded their expectations.
If you place something hot or cold on the forearm of a non-amputee, the latter will feel the effect locally, directly at the place of application. But in amputees, the sensation of temperature on the residual arm can be experienced… in the phantom hand.
Thermal sensory feedback is delivered noninvasively, with thermal electrodes (or “thermodes”) placed against the skin of the residual arm. Thus amputees, like Francesca Rossi, say they feel the temperature in their phantom limb. They can feel the hot or cold of an object, and report whether they are touching copper, plastic or glass. The result of a collaboration between EPFL, the Scuola Superiore Sant’Anna and the Centro Protesi Inail, this technology has been successfully tested on 17 patients, out of a total of 27 people. The results were published on May 18 in «Science».
Jonathan Muheim makes volunteer Fabrizio Fidati smell a glass of iced water via an electrode placed on his arm. Fabrizio has the impression of touching the glass with his finger.
“What is particularly important is that patients perceive phantom thermal sensations in the same way as with their intact hand,” explains Solaiman Shokur, senior lecturer and researcher at EPFL and co-director of the study.
Restore all sensations
“Thermal sensory feedback is essential for relaying information that goes beyond touch. It paves the way for a feeling of affection. We are social beings, for whom heat plays an important role”, explains Silvestro Micera, holder of the Bertarelli Chair in Translational Neuroengineering, professor at EPFL and at the Scuola Sant’Anna, and co-director of the study. “For the first time, after many years of research in my laboratory, where we have shown that we can provide touch and position information, we can envisage restoring all the fine sensations that can emanate from a hand.”
A few years ago, Silvestro Micera and Solaiman Shokur heard of a system, dubbed MetaTouch, which provided thermal sensory feedback through the skin of healthy subjects, also developed at EPFL and developed by the spin-off Metaphysiks. EPFL’s neuroengineering team borrowed MetaTouch, to recreate phantom thermal sensations.
A system that integrates into the prostheses
Then, for this study, Solaiman Shokur and Silvestro Micera designed the MiniTouch: a thermal sensory feedback system specially designed to be integrated into portable devices, such as prostheses. The MiniTouch consists of a thin, portable sensor that can be placed on the finger of a prosthetic hand. It detects sensory information from the touched object, more specifically, the thermal conductivity of the object. If the object is metallic, it will conduct more heat or cold than if it is plastic, for example. A thermode, in contact with the skin of the amputee, on the residual arm, relays the temperature profile of the object touched by the sensor by heating or cooling.
“When we talked about the possibility of regaining thermal sensations on the phantom limb, or that of feeling the contact of various materials, we received a lot of positive comments. Finally, we were able to recruit more than 25 volunteers in less than two years”, explains Frederico Morosato, responsible for the organization of the clinical aspects of the study at the Centro Protesi Inail.
Scientists have found that small areas of skin on the residual arm project sensations to specific parts of the phantom hand, such as the thumb or the tip of the index finger. As they expected, the correspondence of thermal sensations, from the residual arm to the entire phantom limb, is specific to each patient.
An adaptable device for each patient
Almost a decade ago, Silvestro Micera and his colleagues incorporated real-time sensory feedback from grasped objects. Scientists continued to improve touch resolution by reliably providing object texture feedback or positional information. More so, they discovered that amputees begin to embody their prosthetic hand if they receive sensory feedback directly to their intact nervous system. By adding the thermal sensation, they progress a little more towards the design of bionic prostheses to repair the human body. The next step will concern the fine adjustment of thermal sensations and their integration into a device that is adaptable to each patient.
Explanation of how the MiniTouch works.
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