There have been many theories about what actually causes CRPS, but none have been confirmed through research. We do know that the brain responds to a trauma to a limb and instead of sending out the neurotransmitters that reduce pain once the limb begins to heal, the "pain switch" stays "on". Central sensitization is a condition of the nervous system that is associated with the development and maintenance of chronic pain. When central sensitization occurs, the nervous system goes through a process called wind-up and gets regulated in a persistent state of high reactivity. This persistent, or regulated, state of reactivity lowers the threshold for what causes pain and subsequently comes to maintain pain even after the initial injury might have healed. Changes in the dorsal horn of the spinal cord and in the brain occur, particularly at the cellular level, such as at receptor sites.It has long been known that strokes and spinal cord injuries can cause central sensitization. It stands to reason. Strokes and spinal cord injuries cause damage to the central nervous system. What we do not know is how a fracture or sprain in a limb can trigger this response creating CRPS. Research is needed, but funding is limited.