Scientists have used a “breakthrough” approach, that combines virtual reality and artificial tactile sensations, to help two amputees feel as though their prosthetic hand belongs to their own body. The researchers at Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland show that the phantom limb actually grows into the prosthetic hand. The approach, described in the Journal of Neurology, Neurosurgery & Psychiatry, is based on established research on how the brain identifies what belongs to its own body. Instead of using the sense of sight alone, they used an astute combination of two senses: sight and touch.
“The brain regularly uses its senses to evaluate what belongs to the body and what is external to the body,” said Giulio Rognini of EPFL. “We showed exactly how vision and touch can be combined to trick the amputee’s brain into feeling what it sees, inducing embodiment of the prosthetic hand with an additional effect that the phantom limb grows into the prosthetic one,” said Rognini.
The setup is portable and could one day be turned into a therapy to help patients embody their prosthetic limb permanently, researchers said. In two hand amputees, the scientists provided artificial tactile sensations at the tip of the index finger – of the phantom limb – by stimulating the patient’s nerve in the stump. At the same time, the patient wore virtual reality goggles which showed the index finger of the prosthetic limb glowing in synchrony with the administered touch sensations.
This combination of virtual reality with artificial tactile sensations takes the rubber-hand illusion to another level. Both patients reported feeling as though the prosthetic hand belonged to their own body. Moreover, when asked to evaluate the position of their hands, both patients felt as though their phantom limb had extended into the prosthetic limb.
Before the experiment, they both reported that the phantom hand was small and directly connected to the stump, as if the phantom limb had no forearm, a change in size referred to as “telescoping” in scientific jargon. In fact, their phantom limb extended during the experiment, and remained extended for up to 10 minutes afterwards.