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I was very interested by our discussion Tuesday of pain perception.  I have a seemingly chronic pain in my feet caused by plantar fasciitis.  Plantar fasciitis is when the plantar fascia (a ligament that runs along the bottom of the foot attaching to bone at the ball of the foot and at the heel) becomes inflamed.  Inflammation of the plantar fascia can result from not wearing the properly supportive footware, having very high arches, or having very flatfeet, being overweight, from old age, or simply from overuse.  That pain in the bottom of your foot after a long day of being on your feet in dress shoes?  That is your plantar fascia acting up.  Many people experience this sort of short-term pain of their plantar fascia, but with rest the inflammation often goes away within a couple of days.  The physiological cause of inflammation is somewhat unknown; the explanation that I have heard most often is that micro-tears in the plantar fascia are to blame.  The more interesting concern is why does it become chronic in some people (that is, why do they continue to feel pain even when their feet are no longer inflamed)?  Again, this is a question whose answer has not yet been determined.

I have had plantar fasciitis for just about three years now.  There are three ways that I have come to gauge the state of my feet with respect to plantar fasciitis: 1) by how much pain I feel when I am on my feet 2) by how inflamed they seem to be (I find that when my feet are inflamed the pain that I feel is more exhausting and more tender then the pain I feel when they are not inflamed, so I know that my feet are inflamed when I feel this pain, and I also can tell because they will feel hot to the touch and somewhat swollen), and 3) by how thick the plantar fascia seems (supposedly the more thick it is, the more scar tissue and the less thick, the less scar tissue; so a thicker plantar fascia means that my feet have probably been inflamed fairly consistently for a decent amount of time).  When I first got plantar fasciitis, my feet seemed to be inflamed almost all of the time.  For the past six months, I would say that they have actually been rarely inflamed.  The regular pain, however, has been with me every single day of these past three years anytime that I am on my feet whether my feet are inflamed or not. 

It is only when I have bouts of inflammation, however, that I notice that my plantar fascia becomes more thick.  When there is no inflammation and I am just experiencing regular pain, the plantar fascia does not seem to be getting thicker, and often becomes less thick over longer periods without inflammation even though I am still experiencing pain daily.  This seems to suggest that inflammation is causing the damage (the increasing in scar tissue) to take place, but that the regular pain is not causing this damage.  So, pain from inflammation seems to be pain that comes from sensory signals telling my brain that there is something wrong in my feet and actually having something be wrong in them (inflammation causing scar tissue build up).  Why, then, do I still feel pain when there is apparently no inflammation and the scar tissue even seems to be diminishing? 

The way in which corollary discharge plays a role in phantom limb pain illuminates one possible answer in my mind.  In class we learned that pain such as that associated with lost limbs can be caused by a disconnect or contradiction between the signals the brain receives from sensory input and the signals it receives from corollary discharge input.  We also learned that nothing in the nervous system or brain is “hard-wired” because even central pattern generators can change or adapt.  Therefore, perhaps during the initial couple of months of my injury when my feet were constantly inflamed, sensory and corollary discharge signals were telling my brain that my feet were inflamed.  By the time that the inflammation had been eliminated, the corollary discharge signals had become adapted to sensing a certain constant degree of inflammation.  Then, while sensory signals are no longer sensing inflammation, the corollary discharge expects this degree of inflammation any time it realizes I am standing or am putting weight on my feet, and upon not sensing it, it tells the brain that something is wrong and the brain expresses pain.  Although this is just a hypothesis based on our discussion in class, it is exciting to think that maybe my feet are healing even though they don't feel like it, and that one day perhaps the pain will be gone as well when the corollary discharge adapts back to its original state sans inflammation.