"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," says Francesca Rossi.
Rossi is an amputee from Bologna, Italy. She recently
participated in a study to test the effects of temperature feedback directly to
the skin on her residual arm. She is one of 17 patients to have felt her
phantom, missing hand change in temperature thanks to new EPFL technology. More
importantly, she reports feeling reconnected to her missing hand.
"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," Rossi continues.
Researchers Silvestro Micera and Solaiman Shokur have
been keen on incorporating new sensory feedback into prosthetic limbs for providing more realistic touch to amputees, and their latest
study focuses on temperature. They stumbled upon a discovery about temperature
feedback that far exceeds their expectations.
If you place something hot or cold on the forearm of an intact individual, that person will feel the object's temperature locally, directly on their forearm. But in amputees, that temperature sensation on the residual arm may be felt in the phantom, missing hand.
By providing temperature feedback non-invasively, via thermal electrodes
(aka thermodes) placed against the skin on the residual arm, amputees like
Rossi report feeling temperature in their phantom limb. They can feel if an
object is hot or cold, and can tell if they are touching copper, plastic or
glass. In a collaboration between EPFL, Sant'Anna School of Advanced Studies
(SSSA) and Centro Protesi Inail, the technology was successfully tested in 17
out of 27 patients. The results are published in Science.
"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.
Toward realistic bionic touch
The projection of temperature sensations into the phantom limb has led to
the development of new bionic technology, one that equips prosthetics with
non-invasive temperature feedback that allows amputees to discern what they're
touching.
"Temperature feedback is essential for relaying information that goes
beyond touch, it leads to feelings of affection. We are social beings and
warmth is an important part of that," says Micera, Bertarelli Foundation
Chair in Translational Neuroengineering, professor at EPFL and SSSA who also
co-led the study. "For the first time, after many years of research in my
laboratory showing that touch and position information can be successfully
delivered, we envisage the possibility of restoring all of the rich sensations
that one's natural hand can provide."
Temperature feedback, from well-being to prosthetics
A few years ago, Micera and Shokur got wind of a system that could provide
temperature feedback through the skin of healthy subjects, also developed at
EPFL and spun-off by Metaphysiks.
Metaphysiks has been developing neuro-haptic technology, MetaTouch, which
connects the body with digital worlds. MetaTouch combines touch and temperature
feedback to augment physical products for well-being.
"This breakthrough highlights the power of haptics to improve medical conditions and
enhance the quality of life for people with disabilities," says Simon
Gallo, Co-founder and Head of Technology at Metaphysiks.
The EPFL neuroengineers borrowed MetaTouch that provides thermal feedback
directly to a user's skin. With this device, they discovered the thermal
phantom sensations and subsequently tested it in 27 amputees.
The Minitouch prototype and tests
For the study, Shokur and Micera developed the MiniTouch, a device that
provides thermal feedback and specifically built for integration into wearable
devices like prosthetics. The MiniTouch consists of a thin, wearable sensor
that can be placed over an amputee's prosthetic finger. The finger sensor
detects thermal information about the object being touched, more specifically,
the object's heat conductivity.
If the object is metallic, it will naturally conduct more heat or cold
than, for instance, a plastic one. A thermode, one that is in contact with the
skin on the amputee's residual arm, heats up or cools down, relaying the
temperature profile of the object being touched by the finger sensor.
"When we presented the possibility to get back temperature sensation
on the phantom limb or the
possibility to feel the contact with different materials, we obtained a lot of
positive feedback. And eventually, we were able to recruit more than 25
volunteers in less than two years," says Federico Morosato who was
responsible for organizing the clinical aspect of the trials at Centro Protesi
Inail.
The scientists found that small areas of skin on the residual arm project
to specific parts of the phantom hand, like the thumb, or the tip of an index
finger. As expected, they discovered that the mapping of temperature sensations
between the residual arm and the entire projected phantom one is unique to each
patient.
Bionic prosthetics for repairing the human body
Almost a decade ago, Micera and colleagues provided real-time sensory
feedback about objects being grasped. They went on to improve touch resolution
by providing feedback about an object's texture and position information in a
reliable way. Moreover, they discovered that amputees begin to embody their
prosthetic hand if provided with sensory feedback directly into their intact
nervous system.
The added sensation of temperature feedback is yet another step towards building bionic prosthetics for repairing the human body. Fine-tuning temperature sensations and integrating these into a wearable device that can be mapped out to each patient are part of the next steps.
by Ecole Polytechnique Federale de
Lausanne
Source: Bionic prosthetics research: Amputees have thermal sense in missing limbs (medicalxpress.com)
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