Phantom of imagination

A simple treatment for imagined pain in an amputated limb

Published: Friday 30 June 1995

-- (Credit: Malay Karmakar)EVEN the master organ - the brain - can at times get fooled. Sometimes a person feels that a limb that had been amputated is still there but is paralysed. The patient can actually feel all the parts of the phantom limb but cannot move it and this causes extreme discomfort and a persistent pain. Now, Vilayanus S Ramachandran, professor of neuroscience at the University of California, San Diego, has devised a treatment to rid patients of phantom limb pain.

But why does the brain generate a phantom limb in the first place? It seems that when a limb is lost or amputated, the brain modifies its sensory maps. Though the brain no longer gets any responses from the lost linab, it continues to get stimuli from adjacent body parts. These stimuli fool the brain into believing that the missing limb is still there.

For instance, when 28-year-old Derek Steen met with an accident 10 years ago, the nerves in his left hand were damaged and it had to be amputated. No sooner was this done that he started complaining about severe pain where his left hand had been. To treat Steen, Ramachandran came up with an ingenious idea - he constructed a simple box, with a vertical mirror in the middle, having no lid or front and costing a mere us $5 - which he hoped would work.

Steen was asked to place his right hand in the box and move his hand as if he were conducting an orchestra. Seeing is believing. So when Steen waved his right arm, the mirror fooled his brain into perceiving the mirror image as his reconstructed left arm. As he watched his image he got instant relief, but, if he closed his eyes he felt the paralysis return.

But the whole exercise created a conflict in Steen's mind. Explains Ram;chandran, "Steen's vision was telling him that his arm had come back and was obeying his commands. But he was not getting any feedback from the muscles in his arm." This conflict probably told the brain that there was something wrong. But the human brain, especially that of an adult, is rather stubbornly slow in accepting new experiences. So Steen had to repeat the exercise over a period of 3 weeks before his brain saw through the absurdity of the whole thing and decided that it would have nothing to do with it. As a result, for Steen, the phantom limb vanished.

Ramachandran is now using the same technique to treat other kinds of phantom limb pain, including a clenching spasm of phantom hands.

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