Feeling the warmth of your imaginary hand: “My limb is back”

You no longer have hands, but the feeling of warmth and coldness in them. This is what happened to 17 patients thanks to a new technology developed in Switzerland. They had lost their hand due to the amputation, but they could now sense temperature differences in their phantom hand again.

As a result, they experience their missing hand – now replaced with a prosthetic – as a real one. “It doesn’t feel like a ghost anymore, your limb is back,” one of the test subjects told Science. Another patient adds: “The incorporation of hot and cold sensations also improves social interactions in my view.” “When you shake hands with other people, warmth is essential.”

The scientists themselves were surprised by the result. They expected patients to feel hot and cold sensations on their torsos. Instead, they pointed to specific points on a hand drawn in front of them, saying, “I feel it there.” Of the 27 people who took the test, 17 experienced temperature sensations in their missing hands, the researchers wrote in Science.

This technology was developed at the Technical University of Lausanne and works with temperature sensors in the fingers of the prosthesis. These signals are transmitted to the torso of the patient’s arm using heat-sensitive electrodes – called thermodes. Because of this, they perceive the sensation of heat in their missing hands.

The warming and cooling sensation became evident again. This enabled patients to feel the difference between copper, glass and iron. These materials have a similar smooth surface, but they don’t all heat up as quickly as you touch them. Similar techniques had previously been used to make the structure, shape, and hardness of matter tangible, but as far as is known, this has now been done with temperature for the first time.

“It’s a very good study, building on previous work,” says rehabilitation physician Wim Jansen of the Erasmus Medical Center in Rotterdam. He did not participate in the investigation. “The feeling in your hand is crucial. And the feeling of warmth can enhance that.”

the Italian Swiss Researchers have already provided prostheses completely filled with sensors, so that the feeling in the missing hand is stronger. Janssen qualifies this enthusiasm: “My patients are a little more level-headed. They think: If I can’t feel it with my prosthesis, I’ll feel it with the hand I still have.” He therefore does not believe that the new discovery will lead to new prostheses in the short term: “Firstly, the target group is very small, and secondly, this technology will be very expensive.”

He finds the question of how patients might feel heat more interesting. Are there still nerves at the end of the arm that belonged to the missing hand, or did something change in the brain after the amputation? This is simply not known yet, but Jansen thinks about changes in the brain: “Our brain is very ingenious. It has a great capacity for adaptation.”