An unexpected discovery about temperature feedback has led to new bionic technology that allows amputees to sense the temperature of objects—both hot and cold—directly in the phantom hand. The technology opens up new avenues for non-invasive prosthetics.
“When I touch the stump with my hand, I feel tingling in my missing hand, my phantom hand. But feeling the temperature variation is a different thing, something important… something beautiful,” says Francesca Rossi.
Rossi is an amputee from Bologna, Italy. She recently participated in a study to test the effects of temperature feedback directly to the skin on her residual arm. She is one of 17 patients to have felt her phantom, missing hand, change in temperature thanks to new EPFL technology. More importantly, she reports feeling reconnected to her missing hand.
“Temperature feedback is a nice sensation because you feel the limb, the phantom limb, entirely. It does not feel phantom anymore because your limb is back,” Rossi continues.
Researchers Silvestro Micera and Solaiman Shokur have been keen on incorporating new sensory feedback into prosthetic limbs for providing more realistic touch to amputees, and their latest study focuses on temperature. They stumbled upon a discovery about temperature feedback that far exceeds their expectations.
If you place something hot or cold on the forearm of an intact individual, that person will feel the object’s temperature locally, directly on their forearm. But in amputees, that temperature sensation on the residual arm may be felt… in the phantom, missing hand.
By providing temperature feedback non-invasively, via thermal electrodes (aka thermodes) placed against the skin on the residual arm, amputees like Rossi report feeling temperature in their phantom limb. They can feel if an object is hot or cold, and can tell if they are touching copper, plastic or glass. In a collaboration between EPFL, Sant’Anna School of Advanced Studies (SSSA) and Centro Protesi Inail, the technology was successfully tested in 17 out of 27 patients. The results are published in Science. (https://ieeexplore.ieee.org/abstract/document/6775436)
“Of particular importance is that phantom thermal sensations are perceived by the patient as similar to the thermal sensations experienced by their intact hand,” explains Shokur, EPFL senior scientist neuroengineer who co-led the study.
The projection of temperature sensations into the phantom limb has led to the development of new bionic technology, one that equips prosthetics with non-invasive temperature feedback that allows amputees to discern what they’re touching.
“Temperature feedback is essential for relaying information that goes beyond touch, it leads to feelings of affection. We are social beings and warmth is an important part of that,” says Micera, Bertarelli Foundation Chair in Translational Neuroengineering, professor at EPFL and SSSA who also co-led the study. “For the first time, after many years of research in my laboratory showing that touch and position information can be successfully delivered, we envisage the possibility of restoring all of the rich sensations that one’s natural hand can provide.”
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