Virtual reality can help reduce phantom body pain in paraplegics and creates the illusion that they can feel their paralysed legs being touched again, a study has found. The findings could one day translate into therapies to reduce chronic pain in paraplegics.
"We managed to provoke an illusion: the illusion that the subject's legs were being lightly tapped, when in fact the subject was actually being tapped on the back, above the spinal cord lesion," said Olaf Blanke, from EPFL (Ecole polytechnique federale de Lausanne) in Switzerland.
"When we did this, the subjects also reported that their pain had diminished," said Blanke, lead author of the study published in the journal Neurology. Paraplegics suffer from no longer feeling their legs again, but the condition is often accompanied by neuropathic pain due to the spinal cord lesion.
The patient feels pain originating from the legs, even though nothing else can be felt below the lesion. The sensation of pain is real and yet completely resistant to drug therapy. Virtual reality may be the key to providing pain relief for this type of pain, and the solution comes from restoring a sense of touch, researchers said.
"We tapped the back of the subject near the shoulders and the subject experienced the illusion that the tapping originated from the paralysed legs," said Polona Pozeg, neuroscientist at the Lausanne University Hospital (CHUV). "This is because the subject also received visual stimuli of dummy legs being tapped, viewed through the virtual reality headset, so the subject saw them immersively as his or her own legs," said Pozeg.
The experimental setup involves a pair of dummy legs, a camera, virtual reality goggles and two rods. The legs are filmed by a camera. In real-time, the video is relayed into virtual reality goggles worn by the paraplegic patient. The subject sees the dummy legs viewed from above, as if looking down on one's owns legs. With this setup in place, the scientist taps the patient's back with one rod while simultaneously tapping the dummy legs with the other.
Despite being consciously aware of being tapped on the back, the subject still begins to feel as though the tapping comes from the paralysed legs. "It takes about minutes of simultaneously tapping for the illusion to take place," said Blanke. "The tapping on the back gets translated onto the legs because the visual stimulus dominates over the tactile one," he said.
The research pushes the limits of how virtual reality can be used to implement conflicting stimuli, with the aim of ultimately manipulating the brain in how it experiences the body for therapeutic reasons.