Pain and the Perception of Space in Fibromyalgia: Effects of Pain in Estimations of Distance

The Economy of action hypothesis postulates that bodily states rescale the perception of the individual’s environment’s spatial layout. The estimation of distances and slopes in navigation space (i.e. the space reachable by locomotion) is influenced by sensations relating to body condition and the metabolic cost of the actions. The results of the studies investigating the impact of pain on distance estimation remain inconclusive. 28 women suffering from chronic pain and fibromyalgia (FM), and 24 healthy controls (HC) were assessed for musculoskeletal, neuropathic, and visceral pain. In a VR-mediated task, they observed a 3D scenario and estimated the distance of a flag positioned at different distances (1, 2, 3, 4 or 5m) on virtual ramps with either a 4% or 24% inclination. Overestimation of distances in the steeper ramp condition was expected, if participants executed the task by internally simulating the movement. The results showed a dissociation between the effects of musculo-skeletal and visceral-neuropathic pain on distance estimations. According to the Economy of action hypothesis, the HCs estimated the distances as being farther away when the ramp was more inclined (i.e. at 3m and 5m and with a 24% inclination). Furthermore, visceral and neuropathic pain were found to affect the performance of this group. In contrast, there was no effect related to the different ramp inclinations in the FM group, indicating that in the presence of chronic widespread pain, automatic, bodily-based estimations of the potential cost of actions in space are compromised.