Cortical origin of pathological pain.

Pain without accompanying tissue pathology poses a classic puzzle, presented in extreme form by phantom pain in a non-existent amputated limb. A clue to the origin of such pain is given by the recent discovery of a region of cortex active in response to incongruence between motor intention, awareness of movement, and visual feedback. Phantom-limb sensation, and repetitive strain injuries or focal hand dystonias in writers, musicians, or keyboard operators, are accompanied by plastic changes in sensorimotor cortex and by pathological pain. Disorganised or inappropriate cortical representation of proprioception may falsely signal incongruence between motor intention and movement, which results in pathological pain in the same way that incongruence between vestibular and visual sensation results in motion sickness.