Altered visuomotor integration in complex regional pain syndrome

During self-guided movements, we optimise performance by combining sensory and self-motion cues optimally, based on their reliability. Discrepancies between such cues and problems in combining them are suggested to underlie some pain conditions. Therefore, we examined whether visuomotor integration is altered in twenty-two participants with upper or lower limb complex regional pain syndrome (CRPS) compared to twenty-four controls. Participants located targets that appeared in the unaffected (CRPS) / dominant (controls) or affected (CRPS) / non-dominant (controls) side of space, using the hand of their unaffected/dominant or affected/non-dominant side of the body. For each side of space and each hand, participants located the target using visual information and no movement (vision only condition), an unseen pointing movement (self-motion only condition), or a visually-guided pointing movement (visuomotor condition). In all four space-by-hand conditions, controls reduced their variability in the visuomotor compared to the vision and self-motion only conditions and in line with a model prediction for optimal integration. Participants with CRPS showed similar evidence of cue combination in two of the four conditions. However, they had better-than-optimal integration for the unaffected hand in the affected space. Furthermore, they did not integrate optimally for the hand of the affected side of the body in unaffected space, but instead relied on the visual information. Our results suggest that people with CRPS can optimally integrate visual and self-motion cues under some conditions, despite lower reliability of self-motion cues, and use different strategies to controls.