I have been thinking about central pattern generators and corollary discharge signals in regard to phantom limbs, phantom pain, and the possible relationship to chronic pain.

Because of central pattern generators (or what I believe are referred to as neurosignatures in the article "Phantom Limbs") and their corollary discharge signals, the nervous system is able is able to send messages to various parts of the brain that lead the brain into believing a missing limb is present or in the case of paraplegics that limbs are felt. Not only are the CPG's able to remeber that an arm was once present, they are also able to remember pain that was once felt in that limb, phantom pain. Apparently after pain is felt for a period of time CPG's are developed (or enhanced) in a similar manner as CPG's are developed for motion itself. In many cases, I believe most, the phantom pain is untreatable. Narcotics, anesthetics, cutting nerves in various regions, all result in little or no relief of the pain. However, there is one treatment that was developed that resulted in relief for about 60% of the patients treated called DREZ. Interestingly, the treatment relieved the patient of phanton pain, however, the phantom limb remained present.

I believe that there may be a connection between phantom pain and chronic pain. This connection is based on the fact that the nervous systems of vertebrates, (even invertebrates) are very similar. If the nervous systems of vertebrates are similiar, ie , dogs, monkeys, humans, than certainly the nervous systems within the human species are the same, and for that reason, there is no reason to believe that the nervous system between an amputee and a non-amputee are different. Therefore, the ability of an amputee's nervous system to develop CPG's that memorize (so to speak) pain that was once felt in the limb, then a person who suffers from chronic pain (for example, chronic back pain) may be suffering from phantom pain as well. The pain is very real, just as it is for amputees, and as it turns out, many chronic pain sufferers also benefit very little from neuronal surgery to cut nerves, anesthetics, and narcotics. For many chronic pain sufferers, even morphine offers no relief. This similarity among symptoms of pain between amputees and non-amputees triggers the possible connection that at least some of the pain felt by those who suffer chronic pain may very well be a result of CPG's and the corollary discharge signals sent to other parts of the nervous system, just as in phantom pain.

One of the problems doctors face in treating patients with chronic pain is that they do not want to anesthetise the patient to a point that they no longer feel a part of their body. I am thinking that the DREZ treatment should be tested on non-amputee's if it hasn't been already. My reasoning is that although the the phantom pain was relieved, the position of the limb in space and time did not disappear. Possibly, this is indicative that if a limb is present, that the patient will not lose feeling in the limb but may in fact get relief from the pain. Whatever part of the brain is saying "I know where the arm is and what its doing" just may do the same thing in non-amputees.

I am suggesting that since there is so much research in hopes of relieving phantom pain, than perhaps chronic pain should be incorporated into these studies as well, with the thought that the sources of pain are similarly derived and we can therefore work to help two or more populations of people suffering at the same time.

VERY interesting idea, worth someone pursuing (if they aren't currently). Be a little careful though about details. CPG's aren't "memorizing" pain. At least not as we currently understand things (they are just circuits of neurons producing action potentials which cause motoneurons to fire in a particular pattern, and causing other neurons to carry information about their activity to other parts of the brain, the CD). What MAY however be happening in both phantom limb pain and chronic pain is some kind of mismatch between sensory signals and CD's. If this is so, then standard pain relieving procedures may not work, and one wants something that instead affects (possibly) the mismatch detectors (their sensitivity or output). I don't know anything specific about DREZ, but its relief of pain without disturbing sense of existence is very intriguing ... and it might on that account well be explored for possible use in chronic pain. PG