March 22, 2008

New Ways to Relieve Phantom Pain in Amputees

Researchers at University of California, San Diego, reported results of a new study that found amputees find relief from phantom limb pain by simply watching someone else rub their hands together.
The researchers believe the act of watching another person rub their hands together activates the amputee's brains cells, essentially fooling the brain into thinking the amputee's missing hand is being massaged. 

Experts in Britain said this kind of therapy could help amputees as long as they can go along with the illusion.

The brain has mirror neurons that activate when a person performs an intentional action, such as waving, and also when they see another performing the same action.  These neurons are believed to help predict the intentions of others by simulating the action in the mind.

Similar neurons exist for touch, and are activated both when a person is being touched and when they watch someone else being touched.

The researchers explained that the reason people do not always feel what they see happening to others is that sensory cells do not give the right signals, so the person understands the action is not happening to them.

Vilayanur Ramachandran, who led the study, tested the therapy on former soldiers.

In his first test, he used a device he had created called a mirror box.  An amputee puts their remaining hand in front of the mirror and their brain is tricked into believing the mirror image is actually another working limb. While using the box, two of the amputees then had their normal hand touched and experienced the sensation of being touched on their missing hand.

In a second experiment, Dr Ramachandran found that when amputees watched a volunteer's hand being touched, they also began to experience a touching sensation in their missing limb. One participant even said their pain had disappeared for between 10 and 15 minutes.

Dr. Ramachandran believes the amputees "felt" the actions of others because their missing limb did not provide the feedback to prevent the mirror neurons from being stimulated. Without that, there was nothing to tell the amputees they were not literally being touched.

"If an amputee experiences pain in their missing limb, they could watch a friend or partner rub their hand to get rid of it," he said.

Dr. Ramachandran said there could be other applications for the therapy, including assisting victims of stroke.

"If performed early enough, it may also be used to help stroke patients regain movements by watching others perform their lost actions," he said.

Kate McIver of Liverpool University's Pain Research Institute told BBC News that work done at the Institute, using the same basic principle as the U.S. research,  to help amputees create mental images of pain-free limbs had also proved effective.

However, she added that while watching massage could help, "With something external like this, the patient has to accept that the illusion is real for it to work."

The study was reported in the March 20 New Scientist, and can be viewed here.


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University of California, San Diego