Pain and the body schema: evidence for peripheral effects on mental representations of movement.

Some accounts of body representations postulate a real-time representation of the body in space generated by proprioceptive, somatosensory, vestibular and other sensory inputs; this representation has often been termed the 'body schema'. To examine whether the body schema is influenced by peripheral factors such as pain, we asked patients with chronic unilateral arm pain to determine the laterality of pictured hands presented at different orientations. Previous chronometric findings suggest that performance on this task depends on the body schema, in that it appears to involve mentally rotating one's hand from its current position until it is aligned with the stimulus hand. We found that, as in previous investigations, participants' response times (RTs) reflected the degree of simulated movement as well as biomechanical constraints of the arm. Importantly, a significant interaction between the magnitude of mental rotation and limb was observed: RTs were longer for the painful arm than for the unaffected arm for large-amplitude imagined movements; controls exhibited symmetrical RTs. These findings suggest that the body schema is influenced by pain and that this task may provide an objective measure of pain.