Investigating the impact of spatial conflict on the crossed-hands analgesia phenomenon

Details

Supervisors

Legrain, Valéry

Faculty

Faculté de psychologie, logopédie, sexologie et des sciences de la famille

Degree label

Master [120] en sciences psychologiques, à finalité approfondie

Abstract

Considering the posture of a body in pain is crucial to be able to defend the body against the external threatening stimulus that caused the pain. Accordingly, nociceptive inputs have been shown to be 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. The ability to code the spatial location of pain according to these two reference frames has been evidenced, among other, 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 versa”). Hence, this phenomenon is associated with a decreased cortical activity and perceived intensity of the nociceptive stimuli applied on the hands. In order to explain these latter effects, it has been recently hypothesized that the conflict encountered is resolved by realigning the two cortical maps, which requires a cognitive effort. In consequence, less cortical resources remain available to process other stimulus features, such as its intensity. To test this hypothesis, healthy volunteers were asked to rate their intensity perception of nociceptive radiant heat stimuli applied alternatively on both hands dorsum. We compared the intensity ratings between an uncrossed and a crossed hand posture according to two conditions. In a first condition, stimuli were randomly applied on the left and right hands so that the location of the stimuli delivered at each trial was unpredictable. At each trial of the crossed hand posture condition, a conflict would be generated by the automatic activation of the two reference frames. It was therefore expected that crossing the hands during that unpredictable location condition would decrease the intensity ratings of the participants, as compared to the uncrossed hand posture condition (replicating previous data). In a second condition, only one hand was stimulated, making the location of the stimulus predictable at each trial. In this case, it was supposed that the spatial conflict could be resolved before receiving the stimulus. Therefore, the crossed-hand effect on intensity ratings would not be observed in this latter condition. However, we did not observe any crossed-hands analgesia effect, neither in the unpredictable, nor in the predictable location conditions. We therefore fail to replicate previous findings according which crossing the hand affects intensity perception.