Amputees can feel relief from phantom limb pain just by watching someone else rub their hands together, a study says.
Massaging the remaining limb can help phantom pain
The treatment appears to fool the brain that it is their missing hand being massaged, California researchers say.
New Scientist magazine reports that it harnesses nerve cells in the brain which become active when watching someone else carry out an action.
UK experts said this kind of therapy may help amputees, as long as they can go along with the illusion.
Mirror neurons in the brain fire up when a person performs an intentional action, such as waving, and also when they observe someone else performing the same action.
They are thought to help predict the intentions of others by simulating the action in the mind.
Similar cells exist for touch, and become active both when a person is being touched and when they watch someone else being touched.
Researchers at the University of California, San Diego, say the reason people do not constantly feel what they observe happening to others is that a person's sensory cells do not give the right signals, so they know it is not happening to them.
In the study, Vilayanur Ramachandran tested the therapy on ex-soldiers.
His first test used a device called a mirror box, which he developed. An amputee puts their remaining limb, in this case their hand, in front of the mirror and their brain is tricked into thinking the mirror image is actually another working limb.
Two amputees had their normal hand touched while using the mirror box, and felt the sensation of being touched on their missing hand.
In a second experiment, when amputees watched a volunteer's hand being stroked, they also began to experience a stroking sensation arising from their missing limb.
One even said their pain disappeared for between 10 and 15 minutes.
Dr Ramachandran suggested the amputees "felt" the actions of others because their missing limb provided no feedback to prevent their mirror neurons being stimulated, and therefore not telling them they were not "literally" being touched.
He said: "If an amputee experiences pain in their missing limb, they could watch a friend or partner rub their hand to get rid of it."
But Dr Ramachandran said there could be other uses for the therapy, including helping people who have had strokes.
"If performed early enough, it may also be used to help stroke patients regain movements by watching others perform their lost actions."
Kate McIver, of the Pain Research Institute at Liverpool University, said work done there on helping amputees create mental images of pain-free limbs - which operated on the same basic principle as the US research - had also proved effective.
She said watching massage could help, but added: "With something external like this, the patient has to accept that the illusion is real for it to work."