Touching own injury 'cuts pain'

Touching is an important way of sending a picture of our body to our brain

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.