New sensations: This diagram shows how pressure on areas of reinnervated chest skin corresponded to a patient's perceived sensation in the missing limb.

Credit: National Academy of Sciences

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SYDNEY: Amputees could "feel" their lost arms and hands after scientists reconnected nerves to their chests in an experiment that holds promise for providing sensation in artificial limbs.

In two patients who had lost arms, researchers at the Rehabilitation Institute of Chicago and Northwestern University rerouted to their chests key nerves that had transferred sensation from the hand to the brain.

After several months, during which the nerves reestablished themselves in the chest muscles, physical pressure, heat and cold, and electrical stimulus were applied to the chest area and the patients said they could feel their missing arms and hands.

They could sense both touch and temperature, with different areas of the regrown nerves in the chest corresponding to different parts of the missing hand and arm.

"Feeling" in artificial limbs

"This gives them the sensation that they are feeling things with their prosthetic limb," said neurophysiologist Paul Marasco at the Institute's Neural Engineering Centre for Artificial Limbs. The researchers are now working on rewiring nerves to enable amputees to feel pressure applied directly to their prosthetic limb.

They have installed a sensor in the fingertip of a prosthetic arm that can measure how hard an object is being gripped. This information is sent to a plunger device that presses the area of chest skin that corresponds to the fingertip.

"In the future we see refining this approach to better approximate an intact hand," said Marasco. This would include incorporating more sensors and plungers to enable amputees to sense pressure on multiple parts of the hand. It would also involve adding the sensation of temperature.

Rerouting nerves

The study, published today in the U.S. journal Proceedings of the National Academy of Sciences, trialled reinnervation in two amputees who had lost arms. One was a 54-year-old man who had lost both his arms due to electrical burns.

Nerves that once led to the patients' arms were surgically transferred to pectoral muscles in the chest. These reinnervated the overlying skin so that five months after surgery, touching the patient's chest led to sensations perceived as occurring in the missing limb.

"Even though there are slight patient-to-patient differences between how the sensation felt – for example tingling versus pressure – the sensations are always interpreted as occurring in the missing limb," said Marasco.

While the rerouted nerves shared the same skin as the pre-existing chest nerves, the sensations of touch were not confused – the patients sensed touch on the chest independently of touch they perceived as occurring on the missing arm.

In both amputees, nerves leading to the missing limb had not been used for more than a year. This suggests the sensory pathways for the missing limb remain intact despite prolonged lack of use, the researchers said.

According to Jon Kaas, an expert in neurophysiology from Vanderbilt University in Tennesse, USA, "The redirected sensory nerves can be used to produce the sense of touch and pressure as the prosthetic arm contacts objects." This would provide "very valuable feedback " for prosthetic devices, he said.