Wednesday, July 20, 2016

Correlating nociception and pain

I have accepted, over time, that pain and nociception are two distinctly different animals.
Just because my cat eats grass once in awhile, that does not mean that it is a cow.
Yes, nociception can "hurt," but that does not make it pain.

Nociception can be directly measured and pain only indirectly.
And there is enough literature around, drawing the distinction, and slowly dragging us all up out of the muck of biomedical dogma that had the two conflated for so very long, that I seriously doubt there is much in the way of any dependable correlation between the two. OK, I doubt there is any that is relevant to the patient who stands before me. Especially three months in. Three months is the arbitrary length of time, decided by powers that be, when acute pain turns into chronic pain. That's how long it takes soft tissue to heal. (We're talking mesodermally derived soft tissue.) Most of the people I see have had a pain, or pains, for years. Pain is NOT about tissue damage. Pain is about pain. It's an emergent property of the nervous system itself. Nociception might be about tissue damage. Or not. It might only be about tissue danger. Nociception is a signal. Pain is perception, the personal meaning of something perceived as sensation.

Science geeks love correlating things to each other. I'm not much of a science geek. I am not involved in creating any of it.
I love science, but as a consumer, as an appreciator, not a producer.

Correlation has come up as a topic on facebook, specifically correlation between nociception and pain. Some who would proclaim themselves producers, have their hard-won academic black belt, argue with me when I say there isn't any. They think it's laughable, because of course, anything can be forced to correlate to anything else... that's part of the geeky business of it all.
See the Wikipedia entry for spurious correlation.
For some actual spurious correlations, see this link.

As Neil O'Connell PT repeated recently, "If you torture the data long enough it will confess to anything."
Furthermore, about hammering of hands, that demonstrates nothing about how brains respond to nociception, because even hitting a rubber hand that the brain has accepted into its body schema will elicit a protective response, no actual nociceptive input required! Pain (and in this case, protective response) is entirely context dependent!

I get that there is a whole world of measuring and correcting for and determining the Most Precise Measuring and Comparing of Variables that Could Possibly Exist, just as there is for fixing cars. I couldn't be more happy for people who love math and all the patterns they can find in the world, including lovely mathematical patterns in the abstract examination of something as measurable as nociception against something as nebulous as pain.
Nociception is probably causal for pain more than it is correlative. One thing I do distinctly remember from reading science appreciation, is that correlation and causation are also not the same thing, and should not be conflated.

To me, the effort to find a correlation between nociception and pain makes about as much sense as trying to measure the relationship between size of the matchstick, amount of flammable chemical on the end of it, etc. (i.e., nociception) and size of forest fire (pain). Especially when the fire could have been started by an unmeasurable lightning bolt instead. And the size of fire, ultimately, might have been way more about a lack of rain than any other factor or variable, including the match or the lightning. And in terms of pain, sensitization continually adds more fuel. In the end, maybe the creation of a backfire can help stop the spread of the forest fire.

So many variables, that measuring the size of the original match and trying to correlate it to the size of the fire, and seeing that as having any sort of relevance, scientific or clinical, is kinda ridiculous, on the face of it... to me at least.

Furthermore, nociception is not always unpleasant, whereas pain always is.
Here is something I wrote long ago, buried in Facebook somewhere I think, retrieved by Lars Avemarie:
“Nociception is sensation. Pain is a perception. Consider seeing: A sudden flash of light = sensory input. If it gets your attention it might be “sensation”.  But sensory input or even sensation ≠ vision. It does not yet have any assigned meaning. Only context (both inner and outer), considered and added, can provide meaning. A sudden flash of light might be a bomb. Uh-oh, duck and run. A sudden flash of light might be fireworks. Ooh.. pretty. Nociception is not always unpleasant: e.g., rolling around naked in snow, after a 4hr sweat lodge experience. Kinky things SM people do for fun. Nociception ≠ pain. Pain is always UNpleasant.” 


1 comment:

Niels said...

That is so true, and something I think is often being confused for one another.

Especially with chronic pain where there usually is little or no nociception involved in a painful experience. I believe it is essential to appreciate how complex pain is and treat the whole person who is in pain rather than focusing purely on whether there is tissue damage or not, which are poorly correlated by the way.

Thanks for a nice post!