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Thursday, March 13, 2014

Virtual Reality versus phantom limb pain

The majority of people who have had a limb amputated, regardless of the reason for that amputation, suffer from ‘phantom limb pain’. As the name suggests, phantom limb pain is the phenomenon in which a person feels persistent pain or itching coming from a limb that has been amputated. Sufferers will sometimes insist that the missing hand or foot is extremely painful to them. Understandably, this has been difficult for physicians to treat, since there is no hand or foot. Painkillers can be ineffective, and the discomfort can last years or even a lifetime.

At first, phantom pain was thought to be triggered by crushed or damaged nerves at the amputation site. Now, it is known that the discomfort originates directly in the brain. The part of the brain responsible for the missing limb now has no job, and begins to fire when other parts of the body are stimulated. In some cases, stroking part of a patient’s face will create the sensation of touching a missing limb.

That being the case, doctors have had some success at curing phantom limb pain by using mirror boxes to trick the brain into thinking the limb has been resurrected.

There are a couple of drawbacks to this treatment. For one thing, not all patients respond to the visual cues provided by the mirror. Perhaps more importantly, a person must have one completely sound and functional limb for the mirror to work.

Researchers from Chalmers University of Technology and Sahigrenska University Hospital in Gothenburg, Sweden have been experimenting with virtual and enhanced reality systems to get around both of these drawbacks. They use computer algorithms to turn signals from the muscles left at the amputation site into instructions for moving a virtual limb. Because the signals originate in the amputated limb, rather than the opposite side of the body, the sensation is more vivid. Also, no intact limb is required for the therapy.

In the augmented reality environment, the patient can see himself with a superimposed virtual arm, which is controlled by muscle signals from his arm stump.
Credit: Ortiz-Catalan et al., Frontiers in Neuroscience

So far, the scientists were able to bring relief to one patient who had suffered from phantom limb pain since losing his arm nearly 50 years ago. After working with the system once or twice a week for ten weeks, the patient reported his first moments of being completely pain free:
These pain-free periods are something almost new to me and it is an extremely pleasant sensation.
I'm sure it is. And let's hope he and others like him can enjoy many more pain-free moments thanks to this technology.

Ortiz-Catalan, M., Sander, N., Kristoffersen, M., Håkansson, B., & Brånemark, R. (2014). Treatment of phantom limb pain (PLP) based on augmented reality and gaming controlled by myoelectric pattern recognition: a case study of a chronic PLP patient Frontiers in Neuroscience, 8 DOI: 10.3389/fnins.2014.00024.


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