Santa Lucia - Neurosciences and Rehabilitation Sapienza University of Rome

J Pain. 2015 Feb 24. pii: S1526-5900(15)00534-9. doi: 10.1016/j.jpain.2015.02.003. [Epub ahead of print]

Seeing one's own painful hand positioned in the contralateral space reduces subjective reports of pain and modulates laser evoked potentials

Studies report that viewing the body or keeping one's arms crossed while receiving painful stimuli may have an analgesic effect. Interestingly, changes in ratings of pain are accompanied by a reduction of brain metabolism or of laser evoked potentials (LEPs) amplitude. What remains unknown is the link between visual and crossed arms related analgesia. Here, we investigated pain perception as well as LEPs in three visual contexts while participants kept their arms in a crossed or uncrossed position during vision of i) one's own hand or ii) a neutral object in the same spatial location, and iii) a fixation cross placed in front of the participant. We found that having vision of the affected body part in the crossed arms position was associated with a significant reduction in pain reports. However, no analgesic effect of having vision of the hand in an uncrossed position or of crossing the arms alone was found. The increase of late vertex LEP P2 amplitude indexed a general effect of vision of the hand. Our results hint at a complex interaction between cross-modal input and body representation in different spatial frames of reference and at the same time question the effect of visual analgesia and crossed arms analgesia alone.

PERSPECTIVE: We found that nociceptive stimuli delivered to the hand in a crossed arms position evoked less pain than in a canonical anatomical position. Yet, we report no significant analgesic effect of vision or crossing the arms on their own. These findings foster the integration of visuo-spatial and proprioceptive information in rehabilitation protocols.

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