Scientists have developed a device that allows amputees to feel warmth in their phantom hand.
MiniTouch consists of a small sensor placed on an amputee’s prosthetic finger and electrodes that mimic sensations on the residual arm.
The electrodes on the amputated arm are able to relay the temperature of the object being touched by the finger sensor, giving “the illusion that we are cooling down, or warming up, missing fingers”.
The researchers said their findings, published in the journal Science, could allow amputees to have temperature-sensing technology built into their prosthetic limbs, without the need for invasive technology.
The team said they developed MiniTouch after unexpectedly discovering that amputees somehow are able to feel temperatures in their missing hand.
Dr Solaiman Shokur, a neuroengineer and scientist at Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland, said: “We discovered a new mechanism that we call the thermal phantom sensation.”
In an able-bodied person, if something hot or cold is placed on the forearm, that person will feel the object’s temperature directly on their forearm.
But in amputees, that temperature sensation on the residual arm may be felt in the phantom, missing hand, the researchers said.
Dr Shokur said: “(During the tests) we were expecting for them to tell us, with eyes closed, where they felt it (temperature sensations) on the stump, and if it was hot or cold.
“Instead, they pointed into a drawing of a hand that they had in front of them and they told us ‘I feel it there’.
“We asked them several times ‘What do you mean by that, I feel it there?’ and then they clarified that they felt it into their phantom missing hand.
“So this discovery was crucial for us to develop a neurotechnology that could integrate the prosthetic hand of patients.”
The team said they were able to successfully test their bionic technology in 17 out of 27 patients.
MiniTouch uses information about an object’s heat conducting properties to determine how hot or cold it is.
The scientists said they found that small areas of skin on the amputated arm are able to project temperature sensations to specific parts of the phantom hand, like the thumb, or the tip of an index finger.
They also discovered that these temperature sensations between the residual arm and the projected phantom one is unique to each patient.
Fabrizio Fidati, an amputee from Italy, who took part in the study, said: “Warmth is the most beautiful feeling there is… like when we need warmth, we use a hot water bottle.”
He added: “So far, prostheses have mainly been designed to have simple everyday movements, to help you in your everyday life.
“But integrations of sensations of hot and cold, in my opinion, also serves to improve social interactions.
“When shaking hands with people, warmth is… fundamental.”
Study participant Francesca Rossi, also from Italy, added: “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.”