The visual size of one's own hand modulates pain anticipation and perception

How to reduce pain is a fundamental clinical and experimental question. Acute pain is a complex experience which seems to emerge from the co-activation of two main processes, namely the nociceptive/discriminative analysis and the affective/cognitive evaluation of the painful stimulus. Recently it has been found that pain threshold increases following the visual magnification of the body part targeted by the painful stimulation. This finding is compatible with the well-known notion that body representation and perceptual experience relay on complex, multisensory factors. However, the level of cognitive processing and the physiological mechanisms underlying this analgesic effect are still to be investigated. In the present work we found that following the visual magnification of a body part, the Skin Conductance Responses (SCR), to an approaching painful stimulus increases before contact and decreases following the real stimulation, compared to the non-distorted view of the hand. By contrast, an unspecific SCR increase is found when the hand is visually shrunk. Moreover a reduction of subjective pain experience was found specifically for the magnified hand in explicit pain ratings. These findings suggest that the visual increase of body size enhances the cognitive, anticipatory component of pain processing; such an anticipatory reaction reduces the response to the following contact with the noxious stimulus. The present results support the idea that cognitive aspects of pain experience relay on the multisensory representation of the body, and that could be usefully exploited for inducing a significant reduction of subjective pain experience. (C) 2014 Elsevier Ltd. All rights reserved.