[originally published in KCN, May 2008]
The word “Plastic” means different things to different people. We all probably relate to the countless plastic products and materials that we have come to rely on. Everything from drinking cups to dashboards — rain gear to baby toys — traffic cones to sunglasses. Still others might reach for their wallets to show off their “plastic.” And sometimes plastic is the perfect word to describe something that is fake or artificial. But ask a scientist, engineer, or artist to define the word plastic, and you just might be in for an answer that you have never heard before. For these professional fields have definitions of plastic that revolve around a material’s ability to change in shape — much like plastic does when it is heated. Specifically however, when “plastic” is used in the biological sciences it refers to an organism’s ability to “exhibit adaptability to change or variety in the environment.”
Scientists have been discovering that the connections in our central nervous system (ie. brain and spinal cord) are capable of change. In other words, the “wiring” of our bodies, as one might think, is not a blue print that is “set in stone,” but rather one that is dynamic — or “plastic” — and capable of adapting to our environment. This plastic nature of the central nervous system has been commonly observed during the developmental and learning stages of life, as well as other situations such as recovering from spinal cord injuries. It’s the “nervous system memory” that we chiropractors often refer to. It is the expression of our of experiences — positive or negative — that our bodies are continually facing.
This plastic nature of the nervous system is known as “neuronal plasticity” — and we are just grazing the tip of the iceberg on our full understanding of it. It seems that while there are positive aspects of neuronal plasticity (such as learning to use one’s non-dominant hand to perform tasks, or regaining a level of function following intensive rehabilitation for a spinal cord injury), there are also some potentially negative arenas that neuronal plasticity is involved (such as depression, post traumatic stress disorder, phobias, and chronic pain).
Since 1895, chiropractors have been aligning spines to relieve pressure on the nervous system. But are these vertebral misalignments (subluxations) really that big of deal? Sure they often cause pain — but not all the time. Forget about the fact, for a moment, that they set the table for osteoarthritis. If they aren’t squawking loud enough to cause some sort of obvious symptom or restricted function, do we really need to worry about them? Enter our “plastic rats”.
Intrigued by the evolving knowledge of neuronal plasticity, a group of chiropractic researchers set out to ask the question in a pilot study published last summer (June 2007) as to whether or not spinal subluxations were enough of a problem to evoke change in the central nervous system.
For help, they turned to a small group of Sprague-Dawley rats. Utilizing a special, surgically implanted apparatus, the researchers were able to “lock up” three of the rats’ lower back vertebrae, much the same way a subluxation would in a human. After 8 weeks, the rats were anesthetized and their spinal cords carefully examined with an electron microscope. What they found was pretty amazing.
After only 8 weeks of having this artificially induced subluxation, these rats demonstrated neural plastic changes in the dorsal horn of the spinal cord at the level correlating with the locked vertebrae. Specifically, the researchers found a greater density of nerve synapses in the area, compared to the control rats (ie. those rats whose spines were not locked), as well as a change in shape of the nerve synapses which made them more excitatory in nature. In other words, the rats that had vertebrae that were locked up, developed increased — and more sensitive — physically hard-wired changes in the pain sensing portion of their spinal cords; meaning that (if they were still alive) they would perceive pain in their lower backs much more easily than they would have in the past.
So what does this mean to us humans? Technically, nothing. The study was way too small — as it was only a pilot study. But, with these intriguing findings, the door is now open for further, larger studies examining just how the chiropractic subluxation negatively affects our neurology — and, perhaps, even more intriguing, how the chiropractic adjustment plays a role in reversing it.