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 amplitude. What remains unknown is the link between visual analgesia and crossed-arms related analgesia. Here, we investigated pain perception and laser evoked potentials in 3 visual contexts while participants kept their arms in a crossed or uncrossed position during vision of 1) one's own hand, 2) a neutral object in the same spatial location, and 3) 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 the late vertex laser evoked potential 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.


CONCLUSIONS
We found that nociceptive stimuli delivered to the hand in a crossed-arms position evoke less pain than in a canonical anatomic position. Yet we report no significant analgesic effect of vision or crossing the arms on their own. These findings foster the integration of visuospatial and proprioceptive information in rehabilitation protocols.
Psychology Department, Sapienza University of Rome, Rome, Italy; Santa Lucia Foundation, Scientific Institute for Research, Hospitalization and Health Care, Rome, Italy. Electronic address: elia.valentini@uniroma1.it.
Elia
E
Valentini
Psychology Department, Sapienza University of Rome, Rome, Italy; Santa Lucia Foundation, Scientific Institute for Research, Hospitalization and Health Care, Rome, Italy.
Katharina
K
Koch
Psychology Department, Sapienza University of Rome, Rome, Italy; Santa Lucia Foundation, Scientific Institute for Research, Hospitalization and Health Care, Rome, Italy.
Salvatore Maria
SM
Aglioti
D000328:Adult; D000704:Analysis of Variance; D001828:Body Image / Q000523:psychology*; D001931:Brain Mapping; D004569:Electroencephalography; D005260:Female; D006225:Hand / Q000503:physiopathology*; D006801:Humans; D066331:Laser-Evoked Potentials / Q000502:physiology*; D008297:Male; D010146:Pain / Q000503:physiopathology* / Q000523:psychology*; D010147:Pain Measurement; D010812:Physical Stimulation; D011601:Psychophysics; D013028:Space Perception / Q000502:physiology*; D055815:Young Adult
Visual analgesia; crossed-arms analgesia; electroencephalography; laser evoked potentials; pain