A body-part-specific impairment in the visual recognition of actions in chronic pain patients.

Most people suffer musculoskeletal pain sometime in their lives. Although the pain usually disappears with the healing, it may become chronic. Recent evidence suggests that high-level cortical representations play a role in chronic pain. Here we hypothesized that the sensorimotor representations of the affected body parts are specifically inhibited with chronic pain. Thus, if these representations are not accessible for the actions performed by one's own body, neither should they be for the perception of actions performed by others. Chronic pain patients are often focused on possibly painful movements, but visual processes are not affected by chronic pain, so we expected that patients should have no problems recognizing point-light biological motion displays, but should be unable to extract detailed somatosensory and motor information from such displays. Indeed, we found that patients had no difficulty perceiving point-light biological motion, and were not impaired in judging manipulated weight from movements they would be able to perform. However, patients with chronic shoulder pain were specifically impaired to judge the weight from observed manual transfer movements, whereas chronic low-back pain patients were specifically impaired for trunk-rotation movements. This result gives important new insights into chronic pain. Also, this new impairment of biological motion perception is unique in that it is unrelated to visual deficits.