Phantom limb is one of those enduring medical mysteries: that someone could feel sensations in a hand which had long ago been lost to amputation.

A little like harnessing the placebo effect, scientists have been able to stimulate nerve endings on the skin of an amputated arm which trigger thermal phantom limb sensations, including hot and cold.

Adapting one patient’s existing prosthetic arm and socket with sensors and ‘thermodes’ or small devices which can change temperature, placed at these key nerve endings allowed the man to distinguish a hot water bottle from a cold or room temperature one—not because his prosthetic was detecting it, but because his phantom limb was.

“In a previous study, we have shown the existence of these spots in the majority of amputee patients that we have treated,” says Solaiman Shokur at the Swiss Federal Institute of Technology in Lausanne.

Study participant Fabrizio Fidati was able to tell the temperature of a bottle grasped by his modified prosthetic 100% correctly, falling to just one-third without it.

“Warmth is the most beautiful sensation there is,” Fidati told Shokur. “It’s an interesting technology that would serve to improve prosthetics a lot. The integration of these sensations—hot and cold—in my opinion, we need to shake hands (and improve social interactions) with other people… heat is fundamental.”

Shokur said he imagined when testing patients that after the nerve ending stimulation, each subject would point to a certain area on their stump that Shokur’s team was interacting with; exactly the same as if you put a hot cup of tea against the skin on your forearm.

Instead, patients would point to a place on their prosthetic hand and remark that it was here that they felt the sensation, either hot or cold.

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“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.

Another patient, Francesca Rossi, described the feeling as “beautiful,” adding that her phantom limb “does not feel phantom anymore.”

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“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,” she said.

“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.”

WATCH the story below from New Scientist…