Wednesday, May 25, 2011

Hand Pain? Cross Your Arms to Confuse the Brain.

New research suggests that if your hand hurts, simply crossing your arms will confuse the brain and reduce the pain intensity. However, don’t go smashing your thumb to put this to the test — there were limitations of this research to consider first.

Hands Writing in the June 2011 edition of the journal Pain, an international team of researchers report using a laser to produce brief pin pricks of “pure pain” (pain without touch) on the hands of a small group of 8 volunteers [Gallace et al. 2011]. Pain stimuli were then repeated after subjects crossed their arms at the wrists. Subjects rated their pain during each condition and their brain responses to the pain were measured via electroencephalography (EEG).

Results from both the EEG and self-report measures revealed that the perception of pain was weaker when the arms were crossed. In a second experiment, electrically evoked non-painful sensations were applied. EEG and self-report measures were similar to the above findings — crossing the arms reduced perception of the sensations.

Researchers believe this happens because of conflicting information between two of the brain’s image maps: one for the body and a second for external space. For example, there is a cognitive map for the left external space corresponding to the left hand, and one for the right side/right hand. The maps work together, creating brain impulses in response to stimuli. When the arms are crossed, however, the two maps become mismatched and information processing becomes weaker — resulting in less perception of externally applied stimuli like touch or pain.

This might be a possible mechanism behind the analgesic effect of mirror therapy used to treat phantom pain in amputated limbs. In everyday application, the researchers suggest, “Perhaps, when we get hurt, we should not only ‘rub it better’ but also cross our arms.” However, before doing that, there are two important caveats to consider: 1) this was a laboratory experiment in a very small group of healthy volunteers, and 2) the authors concede that the magnitude of analgesic effects from this approach were too small to be clinically important.

So why was this research worthwhile? According to the researchers, it suggests that mechanisms by which sensory events emerge into awareness can also be used to modulate pain, and it could lead to novel clinical therapies to reduce pain that exploit the brain’s way of representing the body.

REFERENCE: Gallace A, Torta DME, Moseley GL, Jannetti GD. The analgesic effect of crossing the arms. Pain. 2011(Jun);152(6):1418-1423 [abstract here].