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Touching own injury 'cuts pain'

2010-09-24 02:49:31

There may be a very good reason why people clutch a painful area of their body

after receiving an injury, according to a study.

Touching the affected area allows a picture of the body to form in the brain,

says a study in Current Biology.

Researchers at University College London (UCL) found that the way the body is

represented in the brain is key to reducing perceptions of acute pain.

But it does not work if someone else touches the injury, they say.

Scientists from the Institute of Cognitive Neuroscience at UCL studied the

effects of self-touch in people who were made to feel pain using an

experimental model called the Thermal Grill Illusion (TGI).

Healthy volunteers were asked to put their index and ring fingers in warm water

and their middle finger in cold water.

This generates a feeling that the middle finger is painfully hot, explains the

study.

Pain relief

Lead researcher Dr Marjolein Kammers said: "The brain doesn't know this is an

illusion of pain but it does allow scientists to investigate the experience of

pain without causing injury to anyone."

The pain experienced by the middle finger reduced most - by 64% - when TGI was

induced in an individual's two hands and then all three fingers on one hand

touched the same fingers on the other hand.

The same level of pain relief was not evident when only one or two fingers were

pressed against each other or when someone else's hand was pressed against the

affected hand.

Professor Patrick Haggard, also from UCL, explained: "We showed that levels of

acute pain depend not just on the signals sent to the brain, but also on how

the brain integrates these signals into a coherent representation of the body

as a whole.

"Self-touch provides strong evidence to the brain about the correlation of

sensory information coming from different parts of the body.

"This helps to give us the experience of our body as a coherent whole," he

said.

Dr Kammers is currently researching whether the pain-relieving effect of

touching fingers and hands together can be replicated in other parts of the

body.

Previous studies of chronic pain, following the amputation of a limb for

example, have shown the importance of the way the body is represented in the

brain when pain is experienced.

Thanks to this study, researchers say they now have an experimental model to

study how the brain's sense of the body influences acute pain.