People tend to clutch a painful area of their body after an injury because it may offer a sense of relief, British scientists have found.
Touching the affected area allows the brain to form a picture that helps reduce perceptions of acute pain, researchers said in the October issue of the journal Current Biology.
'Interestingly, when we hurt our hand, we grasp it with our other hand but are typically reluctant to allow anyone else to touch the wound.' — Study authors
"We show 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," study author Patrick Haggard of University College London said in a release.
In the experiment, Haggard and his colleague studied the effects of self-touch in people who placed their fingers in cold and warm water.
In the experiment, known as the thermal grill illusion, the index and ring fingers are put into warm water and the middle finger in cold water, which paradoxically leads to the feeling that the middle finger is painfully hot without actually causing injury to research subjects.
Right afterwards, these three fingers on the right hand were touched against the same three fingers on the left hand.
"This self-touch caused a dramatic 64 per cent reduction in perceived heat," the study's authors wrote.
The same level of pain relief was not found when only one or two fingers were pressed against each other or when the subject's affected hand was pressed against someone else's hand.
Self-touch provides evidence to the brain about sensory information coming from different parts of the body to build a cohesive whole, the researchers said.
Previous studies of chronic pain, such as the phantom pain that can follow amputation of a limb, suggest the pain appears to lessen with time as the brain updates its representation of the body.
"Interestingly, when we hurt our hand, we grasp it with our other hand, but are typically reluctant to allow anyone else to touch the wound," the study's authors wrote.
"We suggest that modulation of acute pain by coherence of body representation during self-touch underlies this surprising difference."
The new findings suggest therapies aimed at restoring a coherent representation of the body might help, Haggard said.