Acute Pain: We’ve all experienced this before. What happens in the body is the nerve fibres in your finger get activated very quickly (alpha fibres). They transmit the signal to another neuron in the spinal cord that crosses over and goes right up to the relay station in the brain. The signal then goes to the somatosensory cortex and we feel pain. As the tissue damage heals the pain decreases and after about a week there's no more tissue damage and there's no more pain.
With chronic pain something different happens. We may have had some tissue injury – a muscle sprain or strain. While the injury will heal in a few weeks, the pain persists. Months pass and we still have pain, yet the tissue has recovered.
This is in part due to a support cell in the spine called microglia, which have recently been discovered to play a very important function in pain perception. In the previous example when the nerve fibre transmits the signal from the thumb to the spinal cord, there are chemical messengers released that transmit the signal. These substances are taken up by the microglia, and they become activated: stimulating the original nerve cell to release more of this painful chemical. This creates a vicious cycle of positive feedback, where pain is being generated in the spinal cord – not from the damaged tissue.
This pathway within the spinal cord is an example of neuroplasticity: how the nervous system changes in response to stimuli. People with chronic pain may also have central sensitization: The brain is more primed to feel the pain.
The good news is that we rely on this neuroplasticity to resolve the problem. We can re-train the brain and nerves in the spine to respond normally to stimuli. This means that we have to address all the different factors that over-stimulate the nervous system and activate these microglia to create more pain signals.
What about X-rays/MRIs? Studies have repeatedly shown us that disc degeneration is present in most of the adult population, and you can’t tell who is experiencing pain just by looking at an MRI. The most important predictors of chronic disabling pain are not how abnormal an MRI looks, but relate more to how the person responds to their pain. People with the highest risk factors for developing chronic pain typically have many psychological stressors, including depression and anxiety. A leading spine researcher said:
"the development of chronic disabling low back pain is more about psychology then anatomy".
Luckily, there are tools to help address this neuropsychological problem, including cognitive behavioural therapy and hypnosis.