Crossing your arms relieves pain

Published in the current issue of the journal PAIN, the research shows that crossing your arms over the midline (an imaginary line running vertically down the centre of the body) confuses the brain and reduces the intensity of the pain sensation.

Scientists believe that the reason for this phenomenon is due to conflicting information between two of the brain’s maps – the one for you body and the one for external space.

As your left hand usually performs actions on the left side of space (and vice-versa for the right side), these two maps are used to working together to produce strong impulses in response to stimuli. When our arms are crossed, the two maps are mismatched and processing of noxious information is weakened – resulting in less pain.

“Perhaps when we get hurt, we should not only “rub it better” but also cross our arms,” said Dr. Giandomenico Iannetti, lead author of the paper from the UCL department of Physiology, Pharmacology and Neuroscience.

In the study, scientists used a laser to generate a four millisecond pin prick of “pure pain” – i.e. pain without touch - on the hands of a small group of eight participants, which was repeated with the arms crossed. Participants rated their perception of the intensity of the pain, and their electrical brain responses were also measured using electroencephalography (EEG).

The results from both participants’ reports and the EEG showed that the perception of pain was weaker when the arms were crossed.

Dr. Iannetti explains: “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 – for example when picking up a glass of water on your right side you generally use your right hand.

The ability to determine precisely the location of sensory stimuli is fundamental to how we interact with the world; indeed, to our survival. Crossing the hands over the body midline impairs this ability to localize tactile stimuli. We hypothesized that crossing the arms would modulate the intensity of pain evoked by noxious stimulation of the hand. In two separate experiments, we show (1) that the intensity of both laser-evoked painful sensations and electrically-evoked nonpainful sensations were decreased when the arms were crossed over the midline, and (2) that these effects were associated with changes in the multimodal cortical processing of somatosensory information. Critically, there was no change in the somatosensory-specific cortical processing of somatosensory information. Besides studies showing relief of phantom limb pain using mirrors, this is the first evidence that impeding the processes by which the brain localises a noxious stimulus can reduce pain, and that this effect reflects modulation of multimodal neural activities. By showing that the neural mechanisms by which pain emerges from nociception represent a possible target for analgesia, we raise the possibility of novel approaches to the treatment of painful clinical conditions.