There have been some recent changes in the terminology used by scientists to describe pain physiology. For example, the term “nociplastic” was recently coined to describe pain caused by excessive central nervous system sensitivity. The term “central sensitization” relates to a similar idea, but has variable meanings according to different authorities. And the definition for pain itself is also in play, as it was recently modified by the the International Association for the Study of Pain (IASP).
In this post I'll briefly review these new conventions, so we can make sure we know what people mean when they use these them. I will also argue that trying to get too precise with your definitions can generate more confusion than it prevents, especially with complex concepts like pain.
What's in a definition?
I've always been skeptical about attempts to improve the way we define pain. One reason is that we don’t need definitions to understand the meanings of commonly known words that describe common experiences like pain. If I say “I have back pain”, or “my shoulder is in pain”, people know what I mean, even young children. Imagine someone asking: “I don't know what you mean by the word pain, can you give me a definition?” That would be weird.
Another problem with definitions is that they use words whose meanings may be harder to understand than the word they are defining. For example, imagine that we define pain as "an emergent experience of embodied suffering by an agent embedded in a world." To understand what this definition means, I might need to look up four more definitions and maybe take a philosophy class. And there would be no assurance that my understanding would match those of other people, which would make communication difficult.
Anyway, here’s the old definition for pain by the IASP:
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
This definition seems basically OK but … isn’t it just a fancy way of saying that pain is the feeling of a body part hurting? Also, the wording is ambiguous. Does the term “sensory and emotional experience” include tastes, smells, sounds, and sights? The definition does not specify. The meaning of the word “associated” is unclear, and so is “potential tissue damage.” Sorry to be picky, but as a former attorney, I can’t help but notice these things. If for some reason I needed to prove in court that stepping in dog poop while running counts as pain, I would be able to do so under the IASP definition, because it's an “unpleasant sensory and emotional experience” that is “associated” with an activity that could “potentially” damage my hamstring.
Of course we know that the IASP definition for pain doesn't intend to include events like stepping in dog poop. But this is only because we already know what pain means before reading the definition. Common sense and context are doing all the work here, and the formal definition appears to provide little additional benefit. So what purpose does it serve?
Here’s the updated version of the IASP definition. Is it better?
An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage, or described in terms of such damage.
I don’t see much meaningful difference here (and I think it still doesn’t pass my dog poop test.) The big difference is that the new definition is accompanied by six notes, which state some important facts about pain1: