Scientists at the École Polytechnique Fédérale de Lausanne (EPFL), a research institute in Switzerland, have been studying the use of virtual reality to reduce phantom body pain in paraplegics.
Paraplegia is the impairment of motor or sensory function of the lower extremities. It is often the result of spinal cord injury or a congenital condition. Every year, between 250,000 and 500,000 people suffer a spinal cord injury (SCI). In the United States, more than half of individuals with a SCI are considered paraplegic.
Phantom limb pain refers to painful sensations that seem to come from parts of the body that no longer have feeling or are no longer there. For paraplegics, neuropathic pain is experienced in the legs, even though they have no feeling in the lower extremities. This pain can be experienced as burning, shooting, twisting, itching, pressure, “pins and needles”, or electrical shocks, and it is resistant to drug therapy.
Virtual reality reduces phantom limb pain in paraplegics by creating the illusion that the paralyzed legs are being touched. In this study, the researchers lightly tapped on the subject’s back—either just above the spinal cord lesion (lower back) or near the shoulders (upper back). Subjects sat down with dummy legs in front of them. Video of the dummy legs was taken from above, as if looking down on one’s own legs, and the video was shown in real-time through virtual reality goggles.
In the experiment, the scientist simultaneously taps the subject’s back and dummy leg. The subject is conscious of the feeling that their back is being tapped, but after a minute, the illusion takes place. The visual stimulus is stronger than the tactile stimulus, and the subject experiences the feeling that their own legs are being tapped.
In total, there were twenty patients with paraplegia from SCI and twenty healthy control participants. Results demonstrated that the virtual leg illusion was associated with mild analgesia, which is the inability to feel pain.
Restoring a sense of touch is key to alleviating the phantom pain experienced by paraplegics. In this instance, the researchers successfully manipulated the brain-body relationship to alleviate pain. Researchers and technologists are working together to develop digital therapy further for individuals with spinal cord injuries and other chronic pain issues for at-home use.
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