Amputees who experience phantom limb pain can sometimes get relief from an optical illusion. This trick involves looking in a mirror at the reflection of a healthy limb from a certain angle, which causes it to appear where the missing limb should be. Seeing the limb move freely fools the brain into relieving the pain. Now a study suggests this technique might also work for arthritis pain.

Cognitive scientist Laura Case, working in the lab of Vilayanur S. Ramachandran (a member of Scientific American Mind’s board of advisers) at the University of California, San Diego, used a modified version of the mirror technique to superimpose a researcher’s healthy hand over a subject’s arthritic hand, which was painfully constricted or contorted. Subjects mimicked the slow, purposeful movements of the researcher’s hand with their own unseen hand. After experiencing the illusion of their hand moving smoothly, subjects rated their arthritis pain slightly lower than before and had an increased range of motion.

The result suggests that the toxic soup of inflammatory molecules bathing an arthritic joint is not the only source of painful sensations. “The brain has learned to associate movement with pain,” says Case, who presented her results at the Society for Neuroscience meeting last November in Washington, D.C. The illusion provides the brain with a way to disconnect the sight from the sensation. Next, the group will investigate whether this type of mirror therapy might provide long-term benefits for arthritis, a condition that affects about 50 million Americans.

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