Lorimer Moseley: Pain, Stimulus and Meaning
What does it mean when pain changes while the stimulus remains the same? Lorimer Moseley looks at the complexity of pain beyond nociception.
The researchers thought, “Ahhh, pain equals C-fibers plus A-delta fibers.”
Can you see how intuitively sensible and attractive that is? Now, for those of you who have written that down as fact, you should get ready to cross it out.
If that is fact, we should look for a few consistent themes when we look at the relationship between pain and nociception (the sensory nervous system’s response to certain harmful or potentially harmful stimuli).
For example, if nociception is the substrate for pain, if we should see no change in pain without a change in nociception, then we should see no change in nociception without a change in pain.
You can actually test this quite easily. You can do an experiment where you deliver a consistent nociceptive stimulant, which is what we did some time ago.
We had a very cold piece of metal and we put it on people’s hands. We simultaneously showed them a light. We didn’t tell them anything about the light. We just made it very clear the light was coinciding in time and was related to this very cold stimulus.
The light was either red or blue. This is what happened when they saw a red light. This is their pain rating. This is what happened when they saw a blue light. Each of these yellow lines is an individual.
Some of them are not affected in any way. The light color does not affect how much pain they experience. However, some of them have no pain with the blue light and eight out of 10 with the red light.
The stimulus is identical, so there’s a very large variability between individuals, but clearly the systematic effect is the color of this light is changing pain, but not changing nociception. If we put it onto this figure, we would show: C-fibers haven’t changed what they’re doing and A-delta fibers haven’t changed what they’re doing. However, the pain is greater when it’s red and the pain is less when it’s blue.
This is the theme that’s been coming across for 20 years in experimental and clinical data. The critical thing is meaning. It’s all about what it means, and we can capture that as clinicians.
There are a lot of things we can capture. In fact, Americans are better at capturing some aspects that are very important, for example, how you present yourself as a health professional. Americans often wear ties and stethoscopes.
I know a physio friend of mine who wears a stethoscope. He never uses it. He might as well stitch it into his collar. He probably has actually, but he’s convinced it gets him better results. That makes sense to me. It’s all about meaning.
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