Many amputees suffer from mild to severe pain in the lost or “phantom” limb. Previous work — using a mirror box to let subjects see their intact limb move in place of the phantom — showed that the illusion could help alleviate the pain symptoms.A patient undergoes virtual reality therapy to simulate movement of his missing left arm. Courtesy of the University of Manchester.Taking this concept a step further, researchers led by Craig Murray at the University of Manchester in the UK have created a virtual reality system that allows patients to visualize movement in a computer-generated limb that is controlled by movement of the remaining limb.Computer scientist Stephen Pettifer oversaw the technical design of the system, which uses proprietary code and comprises a standard PC running Ubuntu Linux with an Nvidia GeForce 4 graphics card. The equipment includes a Polhemus Fastrak, a Virtual Research V6 head-mounted display and a 5DT 14 data glove from Fifth Dimension Technologies.Five unilateral amputees, including men and women, participated in a trial of the device. They had lost either an arm or a leg at least one year, and as many as 40 years, ago. Over a two- to three-month period, they underwent seven to 10 half-hour sessions in which they moved or bent their virtual limb or used it to handle a ball.All but one subject experienced pain relief after using the system, sometimes lasting for a few days. All reported transference of sensations into the muscles and joints of the phantom limb. The results confirm the promise of the device, and the scientists hope to extend their research to include more participants and to establish how many and how frequent the treatment sessions should be to yield the best results.