Scientists from University College London (UCL) who reported the finding in the journal Pain said they think the reason for the phenomenon is conflicting information between two of the brain’s maps — one for the body and one for external space.
Dr Giandomenico Iannetti, lead author of the paper from the UCL department of Physiology, Pharmacology and Neuroscience, said: ‘Perhaps when we get hurt, we should not only ‘rub it better’ but also cross our arms.
“In everyday life you mostly use your left hand to touch things on the left side of the world, and your right hand for the right side of the world,”
He said this means the brain areas that hold the map of the right body and the map of right external space are usually activated together, leading to very effective pain processing.
“When you cross your arms these maps are not activated together anymore,” he said, leading to less effective processing meaning that stimuli such as pain can perceived as weaker.
In the study, scientists used a laser to generate a four millisecond pin prick of “pure pain” — in other words, pain without touch — on the hands of a group of eight participants. This was then repeated with arms crossed.
Participants rated their perception of the pain intensity, and their electrical brain responses were also measured using electroencephalography (EEG). Results from both participants’ reports and the EEG showed that the perception of pain was weaker when the arms were crossed.
“Perhaps when we get hurt, we should not only ‘rub it better’ but also cross our arms,” Iannetti said.
The researchers hope their discovery could lead to the development of new drugs and therapies to reduce pain that exploit the brain’s way of mapping the body.