Virtual Reality System Helps Relieve Phantom Pain

Scientists at the University of Manchester, UK, said recently that they have developed a virtual reality system that can help amputees cope with phantom pain by giving them the illusion that their missing limb is still there.

The system developed by Craig Murray, PhD, project head, and his team uses a headset and sensors to transport patients into a virtual world where they see themselves with two limbs which they can control and move to do tasks and play games, according to a news story from Reuters.

So far the scientists, who presented their findings at a science meeting in Denmark, have tested it on five patients including a woman who suffered from phantom limb pain for 40 years, Reuters noted. Each patient had between seven and ten sessions lasting 30 minutes over two to three months. Four out of the five who used the system reported improvements in their phantom limb pain.

"One patient felt that the fingers on her amputated hand were continually clenched into her palm, which was very painful for her. However, after just one session using the virtual system she began to feel movement in her fingers and the pain began to ease," Murray said.

The scientists are planning to test the virtual reality system on more patients to identify which amputees are most likely to benefit from it, Reuters noted.

In information about the project on the University of Manchester website, Murray and researcher Steve Pettifer, PhD, describe the "mirror box" research by Vilayanur Ramachandran [Editor's Note: See "Unlocking a Mystery," The O&P EDGE , May 2004.] "...Ramachandran (1993) created a mirror box made by placing a vertical mirror inside a cardboard box with the top removed, in which the amputee places their remaining anatomical limb inside and views a reflection in the visual space occupied by their phantom limb. He reports anecdotal evidence that the box was able to induce in patients vivid sensations of movement originating from the muscles and joints of their phantom limb. For some patients their phantom limb pain was relieved and others were able to gain control over 'paralyzed' phantoms'. The mirror box has also recently been used with similar success with lower-limb amputees, where viewing a reflection of an anatomical limb in the phenomenal space of a phantom limb resulted in amputees reporting a significantly greater number of movements of their phantom limb than with attempted movement alone (Brodie, Whyte and Waller, 2003).

"Blakemore, Wolpert and Frifth (2002) explain the mirror box phenomenon in terms of a central nervous system internal forward model in which the body and its interaction with the world are represented," the web article continues. "The forward model predicts the sensory consequences of motor commands whenever movements are made. This means that the normal experience of a limb is based upon a predicted rather than an actual state. In the absence of a limb motor commands are still made, so that if a prediction of movement is made then movement will be experienced in a phantom limb. However, because the limb does not actually move there is a discrepancy between these predicted and actual states. With time the forward models will adapt to this situation, so that movement is no longer experienced in a phantom even when motor commands to do so are issued. Therefore, when Ramachandran found that a mirror-box was able to restore voluntary movement of a phantom limb, then, according to Blakemore, Wolpert and Frifth (2002), this was because the forward models were updated. The efference copy produced in parallel with the motor commands generates changes in the predicted position of the amputated limb that matched what the amputee had seen in the mirror.

"...that other visual therapies that work in similar ways may also relieve phantom limp pain as well as increasing volitional movement in phantom limbs. One example of this would be virtual reality (VR) technology, such as the combination of an immersive head-mounted display, instrumented peripheral devices, and computer graphics. The proposed research is intended to build upon the insights of Ramachandran's mirror box by producing a similar phenomenon using virtual technologies. VR offers an opportunity to provide a visual representation of the amputee's whole body, including their phantom limb. Unlike the mirror box, which confines participants' limbs to a narrow spatial dimension, VR enables complex hand-eye coordination, and both fine and gross motor movements of the fingers, hand and arm, and toes, feet and legs. Users of such virtual limbs can engage in tasks made impossible by the mirror box, such as pegboard tasks, racket games, ball games, etc. It is hoped that such VEs will prove to be a therapeutic treatment for phantom limb pain, as well as aiding successful prosthesis use.

"This project aims to produce virtual facsimiles of amputees' phantom limbs; to obtain appropriate measurements that enable conclusions to be reached about the efficacy of VR in the treatment of phantom pain; and to obtain appropriate measurements that enable conclusions to be reached about the efficacy of VR in decreasing body image dissatisfaction and encouraging and enabling successful prosthesis use," Murray and Pettifer conclude.

For more information, visit http://aig.cs.man.ac.uk/research/phantomlimb/phantomlimb.php

Virtual Reality System Helps Relieve Phantom Pain

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