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Is the Pain Just in my Head?

Unravelling Chronic Pain - Part 1
For nearly 200 years it was believed that pain was felt only when something harmful generated a message that travelled from the injured site up to the brain.  Pain was the body's warning system that alerted us when something was wrong, and made us act to prevent further damage.

While this simplistic theory holds some truth for acute injuries, we now know that pain, especially longstanding pain, is far more complex.  What we describe as pain is a unique, individual sensory experience that can not only occur out of proportion to tissue damage, but can persist after everything has fully healed.  We can feel pain in a limb with no damage at all, and even when you no longer have a limb!  

Migraine sufferers know too well what severe, disabling, nauseating pain feels like, yet even the best imaging cannot identify anything "injured" as such.  At the other end of the spectrum, research tells us that two thirds of wounded soldiers report little or no pain until much later, with adrenaline and the sheer will to survive suppressing their pain response until they reach safety.  And consider how differently a guitarist and a singer might react with an identical cut on a finger.  The meaning of that particular injury to that person can have a profound effect on one's pain perception, and resultant behaviour.  And finally, the simplistic, unidirectional pain model cannot account for this dilemma of phantom pain that two thirds of amputees experience.

What science now tells us is that we do indeed have tiny receptors for painful or noxious stimuli in nearly all of our tissues - skin, bone, muscle, organs, tendons, blood vessels, etc. - and that these send electronic messages to the spinal cord where they interact with nerve pathways transmitting the information to the "central computer" in our head.  However the brain is not merely a passive receptacle of information, but instead sends up to 200 times the number of incoming signals back down the spinal cord to interact with the upcoming signal.  This descending pain modulation can be either good, or bad.

Think of the bad messages as buckets of petrol that are fuelling a fire.  These are generated by the Stress System - feelings of anger, anxiety, helplessness or lack of control over the pain, fear (about what has been injured, the repercussions, or fear of re-injury), feeling stressed (about work or finances or functional limitations), plus poor sleep, and social isolation.  All these emotions and circumstances can create chemical messages that magnify the upcoming signal at the spinal cord level, and hence increase the pain you feel. 

But now think of the good messages as buckets of water, dampening down the upcoming pain signals.  Think of the winning footballer who doesn't feel those bruises until the following day, or how you may not notice that sore back when you are busy doing something enjoyable.  Acting via the Endorphin System, factors such as exercise, enjoyment, excitement, relaxation, self pride, positive relationships, touch, simply feeling good about oneself, as well as opiate-type analgesic drugs all dump great loads of water to inhibit the ascending pain signals. 

We need a certain amount of fire to trigger a signal up the electrical cable (spinal cord) to the brain.  That is, there is a minimum threshold of painful stimulation to trigger a nerve impulse.  Like a muscle or bone that gets stronger with exercise, this cable gets better at transmitting pain signals when the painful inputs are more constant, or persist for several months.  That is, the threshold gets a lot lower, so that a previously non-painful stimulus can now generate pain perception in the brain.  This concept is called Central Sensitisation, and can become so severe that even light touch or wind on an injured part can be painful, and in fact we know the spinal cord itself can generate spontaneous signals without any peripheral input (eg. phantom pain).

So the pain that we feel is really a complex interaction of various inputs and outputs from the brain and spinal cord, and depends how sensitised the system is.  Pain is very rarely "just in your head", and the evidence for managing persistent pain supports tackling it from many angles.  Read next month's issue for more advice.

Peter Biskup  
B.Physio(Hons), M.Physio(Musc)
APA Titled Musculoskeletal Physiotherapist

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