Researchers at the Swiss Federal Institute of Technology in Lausanne (EPFL) have developed technology that allows amputees to feel cold or warm in their missing hand. The additional sensation of temperature feedback is another step towards building bionic prosthetics for the human body and allowing disabled people to recognize touch. The next steps in this space are to accommodate temperature senses and integrate them into a wearable device.
Through our hands, we can feel many different sensations, such as pressure, pain, vibration, and temperature, which are important for interacting safely and effectively with our environment. This is why technology is focused on developing prostheses for people with hand amputations, through which sensitivity can be restored, which is possible thanks to the use of artificial sensors. A study published in ‘Science’ reported a breakthrough in this area using direct nerve stimulation.
EPFL researchers Silvestro Micera and Soleiman Shoukur are developing ways to incorporate non-invasive sensory feedback into prosthetics. In the current study, they focused on providing a sensation of temperature and made a startling discovery.
Sensation of temperature in ‘phantom’ limbs
The study began with a neuro-haptic device (MetaTouch) applied to the skin, which was originally designed to combine touch and temperature feedback to connect the body to the digital world and enhance physical wellness products.
In intact individuals, when hot or cold objects are placed on the forearm, they feel a local sensation of temperature directly at the site where the object was placed. However, in amputees they found that, thanks to this technique, the temperature felt in the remaining hand could be felt in the missing hand.
The researchers tested the device on a group of 27 amputees and found that 17 participants reported feeling temperature in their residual limbs. The researchers then developed a device called MiniTouch that provides thermal feedback and is specifically designed to integrate into wearable devices such as prosthetics.
How does the sensor transmit temperature?
The device is a slim, wearable sensor that can be placed on a prosthetic finger of a disabled person. The device detects thermal information about the object being touched, specifically its thermal conductivity. For example, metal objects naturally conduct heat better than plastic objects. The non-invasive heating electrode (thermode) is heated or cooled by contact with the skin of the amputee’s left arm, which transmits the temperature of the object the sensor is touching to the ‘phantom’ limb.
In their research they also found that small areas of skin on the residual arm could project sensations to specific parts of the ‘phantom’ hand, such as the tips of the thumb or index finger, producing “thermal maps of the missing hand”. Are. These maps are unique for each participant.
Touch leads to emotion
“The temperature response is essential for communicating information that goes beyond touch, it leads to emotion. We are social animals and warmth is an important part of that,” says Mikera. “After many years of research in my lab showing for the first time that tactile information can be successfully transmitted, we consider the possibility of restoring all the sensations that a natural hand can provide,” he said further.
“When I touch the stump with my hand, I feel a tingling sensation in my missing hand, my ‘ghost’ hand.” Bologna (Italy), and one of 17 study participants who felt a temperature change in their missing hand .
“The temperature response is a good feeling because you feel the limb, the ‘phantom’ limb, completely. It no longer feels absent because your limb is back,” Rossi said.
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