New Swiss technology allows amputees to feel temperature in their prosthetic hand, improving social interactions

No longer having a hand, but feeling warmth and cold in it. That is what happened to seventeen patients thanks to a new technology developed in Switzerland. They are missing their hand due to amputation, but can now feel temperature differences in their phantom hand again.

As a result, they experience their missing hand – now replaced by a prosthesis – as a real limb. “It no longer feels like a phantom, your limb is back,” one of the test subjects told Science magazine. “Integrating sensations of hot and cold also improves social interactions in my view,” another patient adds. “When you shake hands with other people, warmth is essential”.

The scientists themselves were surprised by the result. They had expected that the patients would feel hot and cold sensations on their stumps. Instead, they pointed to specific points on a drawn hand in front of them, saying, “I feel it there.” Of the 27 subjects, 17 experienced the temperature sensations in their missing hand, the researchers write Science.

The technique was developed at the technical university of Lausanne and works with heat sensors in the fingers of the prosthesis. These signals are transmitted to the stump of the patients’ arm using heat-sensitive electrodes – called thermodes. Because of this, they perceive the sensation of temperature in their missing hand.

The sensation of warming up and cooling down became palpable again. That enabled the patients to feel the difference between copper, glass and iron. These materials have a similarly smooth surface, but they do not all heat up as quickly when you touch them. Comparable techniques have previously succeeded in making the structure, shape and stiffness of a material tangible, but as far as is known, this has now been done with temperature for the first time.

“It is a very good study, which builds on previous work,” says rehabilitation physician Wim Janssen of the Erasmus Medical Center in Rotterdam. He was not involved in the investigation. “Having feeling in your hand is a crucial thing. The feeling of warmth can enhance that.”

Of Swiss-Italian researchers already provide prostheses that are completely packed with sensors, so that the feeling in the missing hand is even stronger. Janssen qualifies this enthusiasm: “My patients are a bit 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 think that the new discovery will lead to new prostheses in the short term: “Firstly, the target group is very small, and secondly, this technique will be expensive.”

He finds the question of how it is possible that patients experience the heat more interesting. Are there still nerves in the end of the arm that belong to the missing hand, or has something changed in the brain after the amputation? That is simply not yet known, but Janssen thinks about changes in the brain: “Our brain is very ingenious. It has a great capacity to adapt.”