Considering the posture of a body in pain is crucial to defend it against the threatening stimulus responsible for the pain. Accordingly, nociceptive inputs are mapped according to both somatotopic and spatiotopic frames of reference, respectively taking into account the location of the stimulus on the body surface and the position of the painful body part in the external space. This co-mapping has been evidenced, among others, by applying nociceptive stimuli on the hands crossed over the body midline. This posture creates a misalignment between the two reference frames, and consequently, a conflict between the output responses (“my left hand is in the right side of space", and vice-and-versa). Hence, this phenomenon is associated with a decreased perceived intensity of nociceptive stimuli applied on the hands. To explain this effect, we tested the hypothesis following which the conflict encountered is resolved by realigning the two cortical maps. This process then requires a cognitive effort, leaving out less resources available to process other stimulus features, such as its intensity. Healthy volunteers were asked to rate their intensity perception of nociceptive radiant heat stimuli applied alternatively on both hands dorsa. Intensity ratings were compared between crossed and uncrossed hands postures. In addition, predictability regarding location of the stimuli was manipulated by applying them on one hand (predictable condition) or variably between the hands (unpredictable condition). We did not observe any crossed-hands analgesia effect, and therefore fail to replicate previous findings according to which crossing the hand affects intensity perception.
Van Caekenberghe, Amélie ; et. al. The impact of spatial conflict on the crossed-hands analgesia phenomenon.12th Congress of the European Pain Federation EFIC (Dublin, du 27/04/2022 au 30/04/2022).
