Pain is Weird

This well-produced short video neatly summarizes many of the key points of the content of this article. Great explanation of how pain works! (But their advice about what to do with that knowledge is off-key — more about that in Mind Over Pain › Pain Education › How pain education can go awry.)

Another fine video “summary” of a different sort: this hilarious TED talk about a snake bite and pain neurology. No, really, you will actually laugh! It’s like stand-up comedy. Australia’s Lorimer Moseley, Professor of Clinical Neurosciences and tireless pain researcher, is one of the best public speakers I’ve ever seen — a must-watch for anyone with chronic pain, and the professionals who care for them. Does he say “groovy” just a couple times too many? Maybe! But it is groovy … mate.

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Ramachandran said that “pain is an opinion” — which sounds like a flaky New Age mind-over-matter theory. But Ramachandran is no mystic or guru: he is a neurologist and scientist. This passage is mainly known for the first few words, a pithy statement of the modern understanding of how pain works:

Pain is an opinion on the organism’s state of health rather than a mere reflexive response to an injury. There is no direct hotline from pain receptors to ‘pain centers’ in the brain. There is so much interaction between different brain centers, like those concerned with vision and touch, that even the mere visual appearance of an opening fist can actually feed all the way back into the patient’s motor and touch pathways, allowing him to feel the fist opening, thereby killing an illusory pain in a nonexistent hand.

Phantoms in the brain, by VS Ramachandran and Sandra Blakeslee

He then tells the story of an extraordinary cure of a man with phantom limb pain, tortured by agony in a clenched fist that was not there. With a clever arrangement of mirrors, Ramachandran created the illusion that the man’s amputated arm was restored — a sort of “virtual” limb. The mere appearance of his phantom hand opening and closing cured his agonizing “spasms.” He felt better because of the illusion that he was better — because he thought he was better. The mirror-cure of phantom limb pain is quite one of the most peculiar results in all of pain science.

Since then, “mirror therapy” has been studied and applied in many ways. A 2007 study showed that mirrors aren’t actually necessary to achieve this effect.4 Mirror therapy is probably just a “fun” way to visualize healthy movement — which may also work fine without mirrors.5

There are many stories of people who suffer extraordinary tissue damage and surprisingly little pain, like the Belarusian pilot who crashed and was impaled by a tree branch as big as a fence post, but cheerfully greeted his rescuers by saying, “I am Groot!”6 He continued to joke throughout his care (“Can you take this sliver out, doc?”) and was repeatedly photographed smiling and behaving normally.

Such anecdotes are fairly common; people can be freakishly pain tolerant. But what about the opposite? If “pain is an opinion,” then surely sometimes the opinion is excessively negative…

Pain with little or no injury

Can a nail between the toes actually fool someone into thinking they’ve been impaled? Image courtesy of Andrew Dixon, Radiopedia case 36688. Nail Photoshopped into the image for dramatic effect.

Such stories seem to show that a pain experience can be powerfully modified by the mind, if not conjured out of almost nothing. The best known extreme example was reported in the British Medical Journal in 1995, and has been widely cited:

A builder aged 29 came to the accident and emergency department having jumped down on to a 15 cm nail. As the smallest movement of the nail was painful he was sedated with fentanyl and midazolam. The nail was then pulled out from below. When his boot was removed a miraculous cure appeared to have taken place. Despite entering proximal to the steel toecap the nail had penetrated between the toes: the foot was entirely uninjured.

JP Fisher, senior house officer, DT Hassan, senior registrar, N O’Connor, registrar, accident and emergency department, Leicester Royal Infirmary7

If we accept that story at face value,8 then his pain was a classic “nocebo” — the opposite of a placebo.9 But this is the only widely known or cited example of fear-powered pain.

I know of another anecdote from a professional, about a man who was rescued from agony by learning that his bright red poop was caused not by internal bleeding but… beets! (I tell the whole story below.) Where did all the “agony” come from? Certainly not the beets. It may be hard to distinguish between agony and panic, which is partly the point. This is actually a common example of nocebo in medicine: people eat beets, think there’s blood in the toilet, and call 911. Funny if it’s not you! They don’t all have pain, but some do.

If there are other weird tales of great pain with no apparent cause, they are hard to find. It makes sense that they would be both rare and/or under-reported.11 But they may be the tip of an iceberg of more ordinary cases of pain out of proportion to the injury, which would definitely be under-reported: “injury seemed a lot more painful for the patient than I would have expected” is probably so common that it’s barely worth a story at a dinner party, let alone a formal case report.

There is experimental evidence of pain that is amplified by the mind: for instance, fear of pain makes people more sore for longer after a workout,12 and a bogus pain-enhancing ointment actually made people more sensitive to painful pressure.13

And there are many compelling anecdotes about functional neurological disorders (the fancy way to say “psychosomatic illness”), and “the two most common symptoms are fatigue and pain.”14 (On the other hand, virtually all sources tend to just assume that unexplained pain is psychosomatic.15)

Pain is not in lock-step with damage. And yet that is exactly what nearly everyone assumed for a long, long time. And many professionals, even though they may “know” better, often seem to forget how powerfully pain may be influenced — for better or worse — by perception, context, and meaning.

What is surprising is how malleable pain signals are—how readily the intensity of a pain signal is changed by the sensations, feelings, and thoughts that coincide with the pain. … The brain is not a mindless pain-ometer, simply measuring units of ouchness.

Why Zebras Don’t Get Ulcers, by Robert M Sapolsky, 187, 193

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For most of the history of medical science, pain was believed to work more or less the way the French philosopher René Descartes described it: a simple signalling system.

1. The flesh is wounded. (“It’s just a flesh wound!”)
2. Nerves send an unambiguous message to the brain about the damage. The intensity of the message is directly proportionate to the severity of the injury.
3. The brain interprets that message at face value — that is, if the message says, “There’s some bad damage here,” we believe it.

Based on this model, almost everyone still — today, in 2024 — assumes that any message sent to the brain by a certain kind of nerve will always cause pain. Health care professionals everywhere still believe that the nerve is “sending pain,” that the signal is pain — and therefore these nerves are habitually called “pain fibers” and their messages are called “pain messages,” an equivalence between signalling and pain baked right into the language.

All of that is badly wrong. And it’s worse than an understandable oversimplification. It’s really very wrong. In fact, it is now known as the “the naïve view” of pain!16

The labeling of nociceptors as pain fibers was not an admirable simplification, but an unfortunate trivialization under the guise of simplification.

The relationship of perceived pain to afferent nerve impulses, by Patrick Wall and SB McMahon, 254–255

The naive view has been replaced by the neuromatrix

The first dent in that old pain paradigm came in 1965 with gate control,17 which showed that other inputs can pre-empt pain (counterstimulation). That was the first strong evidence that pain isn’t a completely predictable response to noxious stimuli.

Ever since, it has become increasingly clear to pain scientists and neurologists that the simplistic pain-fiber model is hopelessly inaccurate. Even microscopic worms with only two trouble-detecting nerves have context-sensitive pain experiences.18 Even their pain is an “opinion,” an interpreted experience. And of course it makes complete evolutionary sense. Pain is clearly a more useful experience when it is “smarter.”

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Pain is usually less intense when we feel safer. This was demonstrated early in the history of pain research by a famous paper about wounded soldiers in WWII: they experienced surprisingly little pain, despite severe injuries, probably because they were just so glad to be off the battlefield.19 Ever since, researchers have been trying to understand how that actually works, and these days we have a pretty good idea.

The brain is not just a passive, gullible receiver for whatever messages the peripheral nerves send upstairs. And, if you think about it, it’s kind of strange that we would ever have thought of it that way, because this is, after all, the brain we’re talking about: seat of consciousness, the generator of your reality. Brains critically evaluate all the danger messages and put them in context before deciding how seriously to take the situation.

Once a danger message arrives at the brain, it has to answer a very important question: “How dangerous is this really?” In order to respond, the brain draws on every piece of credible information — previous exposure, cultural influences, knowledge, other sensory cues — the list is endless.

Pain really is in the mind, but not in the way you think, Moseley (TheConversation.com)

As if that didn’t complicate things enough, once your brain has made up your mind, it also sends messages downwards that actually affect the function of the peripheral nerves.20 Thus everything that hurts involves a conversation, a sort of debate between the central and peripheral nervous systems. It could be dramatized like this:

The brain can even boss the nerves around, tell them how sensitive to be. When anxious, the brain might request “more information” from the peripheral nerves, ordering them to produce more signals in response to smaller stimuli. Or it might do exactly the opposite. There is extensive recent evidence that the peripheral nerves can even physically, chemically change, perhaps in response to brain requests, tissue conditions, or both. To extend the analogy, this isn’t just twiddling the volume knob, but changing the equipment, changing the signal before it even gets to the “amplifier.”

(Just for fun, have a look at the complex version of that diagram. SHOW)

In short, messages don’t just go up to the brain, they go down. This two-way functionality in the pain system is the main difference between modern pain science and old-school pain science.

But most of the modulation is probably central: we only feel what our brains allow us to feel. Even “loud” sensory messages can be filtered down to almost nothing by the central nervous system … or, conversely, “quiet” sensory messages can be amplified. The quality and intensity of the final experience is clearly the product of an elaborate set of neurological filters.

Perhaps many patients whom doctors treat as having a nerve injury or a disease have, instead, what might be called sensor syndromes. When your car’s dashboard warning light keeps telling you that there is an engine failure, but the mechanics can’t find anything wrong, the sensor itself may be the problem. This is no less true for human beings. Our sensations of pain, itch, nausea, and fatigue are normally protective. Unmoored from physical reality, however, they can become a nightmare … hundreds of thousands of people in the United States alone suffer from conditions like chronic back pain, fibromyalgia, chronic pelvic pain, tinnitus, temporomandibular joint disorder, or repetitive strain injury, where, typically, no amount of imaging, nerve testing, or surgery manages to uncover an anatomical explanation. Doctors have persisted in treating these conditions as nerve or tissue problems—engine failures, as it were. We get under the hood and remove this, replace that, snip some wires. Yet still the sensor keeps going off.

So we get frustrated. “There’s nothing wrong,” we’ll insist. And, the next thing you know, we’re treating the driver instead of the problem.

Scratching an itch through the scalp to the brain, by Atul Gawande

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If pain isn’t merely a response to signals from the tissues, what is pain actually a response to? Here’s a slightly more formal and technical explanation….

Pain is the output of a dazzlingly complex threat-detection system that generates pain experiences roughly in proportion to perceived threat, based on all kinds of sensory inputs as well as their meaning and context.

All that input produces the neuromatrix: a distinctive, fingerprint-like pattern of neurological activation determined by genetics, experience (especially trauma), and finally by our immediate situation.21 Disturbances in the neuromatrix produce pain, which might not be triggered by anything obvious or familiar.

You can think of the neuromatrix as a virtual model of your body: if the model hurts, then you hurt.

So the way pain really works is much more complicated, interesting, and in some ways useful than the naive view.

Pain is a complex and multidimensional experience produced by multiple influences.

Ronald Melzack and Joel Katz (2013)

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There is technically no such thing as a “pain signal,” and a nerve should never be called a “pain” nerve. It doesn’t detect “pain.” It only detects some kind of stimulus in the tissue … and the brain decides what to make of it, how to feel about it, and what to do about it, if anything.

So what do they detect, if not pain? Noxious stimuli. And what are those nerves? Nociceptors.

Nociception is the conversion of noxious stimuli into nerve impulses — raw data about possible threats that might lead to an experience of bain, if the brain sees a need… which it routinely doesn’t.

In fact, we are constantly exposed to lots of minor noxious stimuli without pain.

On the other hand, major sources of nociception usually do lead to pain — like from a burn, cut, or stepping on a Lego on your way to the bathroom at 2am. There is a practical equivalence between nociception and pain. Most things hurt.

But not always. And pain might be possible without any nociception at all (although this is controversial, see above regarding alleged examples like Boot Nail Guy). More likely, pain can be quite out of proportion to nociception. This is the main kinds of weirdness that this article is all about, and why the definition of nociception matters to a lot of people with serious pain: it’s a key technical detail about how pain works. The difference between pain and nociception is critical to understanding the weirdness of pain.

For everyone else, it’s mostly splitting hairs, a level of precision we don’t need to use in most communication about pain — like talking about quantum physics when classical physics is all you really need. Your doctor will probably be very puzzled if you say, “I have a pain, but I can’t figure out the source of nociception. Or maybe there isn’t one. Can you help me sort that out?”

But knowledge is good. I also don’t need to know as much about wiring as an electrician, but I am still happy to learn whatever I can about it.

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Thanks to a couple quirky studies in 2010 and 2014 study, science has confirmed that being in love relieves pain — a lovely example of the potential power of the mind over pain.2223

Falling head-over-heels is not exactly a convenient solution, however. As researcher Dr. Sean Mackey put it, “We can’t give you a prescription for love” — not one that’s easy to fill, anyway.

But we can work to give love more of a chance to grow and thrive. You can’t benefit from the pain-killing effect of love if you aren’t in love, and there are obviously ways to improve your chances of getting there.

Closely related: pain is also muted when romantic partners hold hands.24 Aw.💕

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If you view a painful hand through a magnifying glass, it will actually get more swollen and inflamed — that is, if you make it look bigger, it will feel like a bigger problem.25 And the reverse is true too! Use optics to make it look smaller, and swelling will go down. Incredible, right? Jedi pain tricks! But … do you have a de-magnifying glass handy? Where do you buy even one of those, let alone a big one? (They really are hard to find. How about looking backwards through binoculars? Not a great solution.26) And what happens if the pain isn’t in a place that’s so easy to de-magnify, like your low back?

The de-magnification trick is dang interesting, but it’s obviously not a practical approach to most pain. The effect is real under the right circumstances, but trying to use it as a treatment is like trying to take a magician’s trick home with you.

Maybe someday virtual reality tech will make “visuotactile illusions” like this a lot more accessible and convenient. A nifty proof-of-concept study demonstrated that a couple of other illusions can reduce osteoarthritis pain by up to 40%, at least temporarily.27 So what visual sorcery can kill more pain than any other known treatment for that condition? Two similar illusions, using virtual reality goggles to make it look like the knee was either shrinking or stretching. 😜 Whoaa, duuuuude …

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Getting an injection actually hurts less when you don’t watch.28 Out of sight, out of mind: if the brain can’t see the threat, it is less sensitive to it. That’s interesting, and like the magnification/stretching/shrinking experiments, it clearly demonstrates that the brain modulates pain and, in that circumstance, we can modulate it. It’s easy to look away from a needle, but with most chronic pain, what is there to avoid looking at? We usually can’t see the threat.

Although it is technically the brain’s prerogative to ignore painful signals from your tissues, that doesn’t mean that there’s any way we can convince it to do so — if there is a destructive disease process going on, for instance, the brain will usually not ignore those signals! The pain system evolved to report problems, and you can count on it to do so most of the time.

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This is a photo of three-legged cat Isaac, trying to scratch himself with his missing leg:

Now a little to the left … Photo by Reddit user ElenTheMellon.

That has got to be super frustrating! The pathetic futility of Isaac’s scratching does not stop his brain from trying. Poor little guy! His brain has a picture of how things should be, and he acts accordingly. The impulse is like a freight train, irresistible even when it’s blatantly ineffective.

So it often is with pain: if the brain believes there’s a threat, you’re going to hurt, no matter how pointless it is or how intensely you focus on trying to have more reasonable and rational sensations. It’s mostly just not up to you.

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This one’s from my own medical history, in the aftermath of corrective eye surgery in 2011, and some odd consequences shed good light on how pain works: insight from eyesight. Recovery went well initially; a few weeks later, my optometrist couldn’t even find any sign that anything even happened to my left eye. No laser tracks. No remaining signs of recovery. It was ahead of schedule.

But my right eye was a bit blurry, and it ached. In reality, it was also healing on schedule — but it was lagging behind the ahead-of-schedule left, and it was freaking me out a bit. Get a load of what my science-minded optometrist said (paraphrasing) when I told him about this:

People’s eyes often hurt when they think there’s something wrong with them.

That demonstrates that “pain is an opinion” rather well. My optometrist described the following scenario (paraphrasing):

Someone can “discover” an eye problem they’ve had for twenty years and start hurting. They accidentally cover one eye while watching television, happen to notice that the vision in the free eye is a bit off. It’s been off all along — almost everyone is at least a wee bit astigmatic, but the brain completely takes care of that when both eyes are open. But if they notice it with an eye covered, a week later they’re in my office complaining of blurred vision and an ache.

Fascinating. I was paying close attention to my vision in the aftermath of the surgery — probably too close. I “discovered” that the right wasn’t as good as the left, and started checking it even more obsessively. And so it started to ache. And yet it’s only problem was being less awesome than my left. Good grief.

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Sensation and pain are nothing if not mercurial. On the one hand, we can be driven half out of our minds by a bit of beef wedged between a couple teeth. Or, stuck right in the other hand, a large piece of metal can be painless for 50 years. Like a turn signal lever.

Art Lampitt got one of those embedded in his arm in a car accident long ago. What with all the other injuries, no one noticed. It didn’t give him any trouble until recently. His arm began to ache and swell and an x-ray revealed a strange, thin third arm bone.

“I was hoping it might be shiny still,” he said in an interview with CBC Radio One’s “As It Happens,” but it was badly corroded — perhaps the reason it finally caused some symptoms, but who knows.

I love medical marvels that challenge our preconceptions about what will hurt. It’s noteworthy that it didn’t hurt for decades — because if that’s possible, just imagine how unpredictable the symptoms of a little arthritis can be — but it’s also noteworthy that it did start to cause trouble eventually. It’s a great example how pain is weird.

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Beets are the most common source of “blood” in the stool and urine. Photo by Evan-Amos.

This next example is extracted whole from Marni Jackon’s superb book, Pain: The science and culture of why we hurt. This is an amazing anecdote about the power of perception, and what I want to highlight here is that this wasn’t just a case of medical fear and panic: it was a painful experience.

“There are psychic factors involved in every patient’s complaint of pain,” [Bill Livingston] wrote. He tells a story of one midnight emergency to illustrate his point.

A woman called him to report that her husband had just had a “massive bowl hemorrhage and was in a state of collapse.” Just before bed, he had felt some cramping pains and hurried to the bathroom. Then she heard him calling her name, followed by the thud of him falling to the floor. She found him unconscious, white-faced, and covered in sweat. And in the toilet there was a quantity of bright red blood.

Livingston told her not to flush the toilet and rushed over. He found the man lying on the bed, conscious, but in pain. Where does it hurt the worst, Livingston asked. “All over,” the man whispered. He went on groaning as his wife said that he had been in fine spirits and good health, until he had gone to the bathroom.

Livingston examined him, to no avail. Then he went into the bathroom and inspected the alarming-looking contents of the toilet. Beets. Lots of beet fragments. It turned out that her husband had eaten beets for lunch, and little else. Livingston decided that this accounted for the “hemorrhage” and that the man’s state — the pallor, the sweating, and the “all over” pain — had been entirely caused by fright.

The two of them walked back into the bedroom with smiles on their faces, which annoyed the husband, who was languishing on the bed. But when Livingston gave him his diagnosis, the man’s condition improved rapidly. “Within half an hour he was moving about in his usual energetic fashion and offering to pour me a drink if I would stay and chat.”

It hurt all over. Because his brain absolutely believed he was in terrible danger. And no other reason.

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In the weird world of pain, fearing the worst is at least partially a self-fulfilling prophecy: the more worried you are, the worse things tend to do. There are many examples of this, but this is a good fresh one, and I also like the fact that it’s about something people don’t usually as associate with psychology: knee replacement.

Dr. Gary J Macfarlane, regarding a paper on knee replacement results:

“We identified 3 distinct response trajectories in patients undergoing knee replacement. Expectations of pain/limited function and poor coping strategies differentiated the trajectories, suggesting a role for preoperative psychosocial support in optimizing the clinical outcome.”

Although this evidence doesn’t show it, it also seems reasonable to assume that the reverse is true: if worry is worse, probably hope helps. So anything at all that increases patient optimism and confidence is a good idea.

It’s also a dilemma for health science reporting and clinicians: truth may be harmful! The discouraging reality of side effects, poor outcomes, and other bad science news — and there’s a bunch of bad news about knee replacement, — will make patients more pessimistic and fearful, and therefore will actually causes worse outcomes. But we cannot lie or conceal the truth, either! Awkward. 🎵 The truth may be problematic, but also unavoidable and essential. There is no easy solution to this dilemma.

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This example of pain weirdness does not have the charming narrative appeal of some of the stories above, like being in agony from mistaking beet juice for blood. It’s abstract, technical, and hypothetical.

But still very cool.

In the beet juice example, we can see a strong element of behaviour in the pain, a complex response to a perceived threat. And behavioural responses to stimuli can be learned. And it’s possible that this is the nature of some chronic pain. What if your brain just kept believing in a threat? What if there was no doctor to reassure you that it’s just beet juice?

Many perceived threats cannot be easily defused and may continue to produce a complex behavioural response that includes pain. In other words, some chronic pain might be a “learned response” to things that shouldn’t hurt: classical conditioning, like Pavlov’s dogs salivating to the ring of a bell. This is a hypothesis. It is plausible enough to be taken seriously, but unproven and strange enough to be rather exotic.

And it gets weirder!

It’s also possible that learned pain can be un-learned. In the fairly well-established neurology of classic conditioning and memory, responses to stimuli are neurologically re-saved every time the stimulus occurs (“reconsolidation”), and that process can be “disrupted.” The hypothetical part is not whether reconsolidation happens or that is can be disrupted (it does, and it can). The question is whether any of that weird neurology is applicable to pain. It might be, but no one knows yet.

Can pain be a “behaviour” in response to stimuli? If so, it can probably be disrupted. That’s the cool hypothesis. That’s the (hypothetical) weirdness.

If so, it’s as much of a “hack” for pain as I can imagine. I discuss this intriguing idea more thoroughly in Chronic Pain as a Conditioned Behaviour.

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“Forgetting pain” would be an amazing and profound phenomenon… if it actually happens.

Back in 2007, Choi et al. reported two cases of amnesia (different causes) preceding relief from severe chronic pain and the end of any need for opioid management.36 The bizarre and profound implication is that amnesia relieved the pain. 😮

Unfortunately, these stories may not be what they seem, and I cannot take them too seriously.37

But what if amnesia actually did give those people serious relief?

That would suggest that chronic pain is forgettable, and therefore that it was a function of the mind to begin with, something constructed by our brains and therefore dependent on them … to a shocking degree (in these cases, at least). It could mean that pain as a function of identity, of what we think we know about ourselves, implying that this kind of pain cannot persist without context and meaning. It would support the specific premise the authors’ propose: “Nociceptive pain and its emotional component can result in the development of a ‘chronic pain memory’.”

If so, that would not imply that we “control” pain, of course. It would not mean that we can either create or relieve pain with our thoughts, because our “thoughts” are only a small part of what goes on between our ears. We have no more control over what we remember and what it means to us than we have over a phobia or flinching away from a flame.

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Is your pain a throbbing pain? Pain often has a pulsating quality, especially when it’s severe and acute. If you’ve ever thought about why it pulses, you probably assumed that it’s pulsating with your pulse. Heck, “pulsatile pain” is actually a clinical term used to describe throbbing pain that is assumed to be surging in time with the arterial pulse.

I have always particularly noticed the throbbing of infections — like a hangnail that’s gotten out of hand — and I always thought that I was feeling the blood pushing through the ultra-sensitized tissue.

But Mirza et al. checked that assumption… and got a fun science surprise.38

They checked in a bunch of patients with jack-hammering dental pain, getting them to tap out the rhythm of their throbbing with a button… and discovered that their throbs were actually much slower than their heart rates, almost half the pace, just not in sync. They were clearly different rhythms! Not so pulsatile after all.

That’s a fascinating upset to conventional wisdom. (About a very minor thing, sure, but still…)

So what is setting the pace?

The authors took a crack at speculating about what was setting the rhythm of their subjects’ dental throbbing: “an emergent property, or perception, whose ‘pacemaker’ lies within the CNS.”

They confirmed the same pace difference in a follow-up study of a woman with a very different kind of pain, chronic migraine: her head throb was quite a bit slower than her heart rate (48 bpm vs 68). Analysis of her EEG showed that activity in the alpha range (8 to 12Hz) was linked to “greater throbbing intensity” — more alpha oomph came with more fiercer throbbing.39

Reality is always messier than either the conventional wisdom or a slam-dunk of a debunk. The safe bet is that there are several kinds of throbbing pain. I doubt anyone will be checking them all anytime soon, so we can just enjoy the uncertainty indefinitely. But I definitely suspect that some of our throbbing pains truly are pulsatile. Like that infected hangnail, maybe. Ow … ow … ow … ow … ow…

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Pain sensation and perception can be badly distorted in various ways, and that is weird and cool and nasty, but also probably quite rare. We probably can make pain up out of thin air, or almost, but we rarely do. And we can have bizarrely painless trauma — like the soldier who barely feels his wound — but we rarely do. All the famous and fascinating examples are famous because they are a bit exotic (and maybe even too “fascinating” to be true).

For most people, most of the time, pain is not weird. It is usually a consistent, predictable, and sensible warning system about tissue danger — just like the “naive view” always assumed. The boring-but-basic reality is that tissue trouble almost always leads directly to pain. Just because that correlation can get messy and break down does not mean that it always does. Pain must be a mostly reliable signal, that’s why it exists (for the same reason reflexes must be).

And another thing: not all chronic pain is dysfunctional. Just because it seems to be dragging on for no good reason doesn’t mean there isn’t actually still a good reason. Sensitization isn’t the only possible explanation for pain that has no other obvious cause.

Much is made of the difference between acute pain and chronic, generally assuming that acute pain is accurate, while chronic pain is exaggerated or outright bogus. But there’s another important possibility: accurate acute pain that just keeps happening, a renewable resource, an ongoing credible threat to tissues that the brain should take seriously.

Some ongoing causes of pain — a thorn, an old wound, a tumour — are almost too obvious to be worthy of mention. But the cause of persistent pain is often baffling because many “thorns” and “old wounds” are largely invisible, and some tumours are really hard to find.40

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When there’s no clearly diagnosable cause for chronic pain, there are only two possible explanations in principle (aside from outright hypochondria):

1. either there is tissue insult (a source of nociception) that just can’t be identified (surprisingly common I think), or
2. the relationship between tissue insult and pain has broken down (also quite common).

And, of course, it could be a blend.

In other words, the alarm of chronic pain might be false, or it could be true, or somewhere in the middle. Sussing out the difference is a huge clinical challenge and another face of pain’s weirdness and complexity.

In this case, the weirdness is just as much about our lack of clearly labelled concepts as it is about the nature of pain itself. There actually isn’t even a term for an ongoing or recurring cause of chronic pain, so I call it “chronic-acute” pain — but that’s just my informal, descriptive term. A more technical description could be persistent nociceptive pain.

Naming it is valuable. The mere existence of chronic-acute pain is an important source of hope and reassurance for many people, because it means that a “thorn” could still be found, and pulled out.

I’m speaking both professionally and personally here. I once had a persistent pain with no apparent cause, and I was told by a series of professionals that my only problem was pure “false alarm.” But then, better late than never, the %#!!$& source was found and removed … and that was the end of my pain. Ta da! My “thorn” was found and removed.

So I suffered a year of serious chronic pain with no apparent source that absolutely was positively, strongly correlated with a tissue insult. My brain was not lying. The alarm was not false. There was just a sneaky reason for it.

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Many moons ago I started trying to understand and explain pain, gradually producing this article, only dimly aware as I worked that I was re-producing some much more mature ideas.

I knew that modern pain science and treatment has deep roots, insights and research going back to the 1960s and Melzack, gate control theory and cognitive behavioural therapy, but my explaining was eerily similar to a recent and popular “packaging” of pain science known as Explain Pain (EP), from Drs. Lorimer Moseley and David Butler: “a range of educational interventions that aim to change one’s understanding of the biological processes that are thought to underpin pain as a mechanism to reduce pain itself.”44 There’s a book of that name — Explain Pain45 — and many other interpretions and riffs on the key ideas (like this article).

It’s not that I invented my own version of Explain Pain independently, despite how it looks. I was just trying to explain pain, you know? Lowercase!

Explaining Pain, according to Dr. Moseley, is about “wanting people to actually understand how and why they can be in horrible pain yet not in horrible danger.”

Butler & Moseley’s extremely influential book, Explain Pain. The elevator pitch and the central claim of the book, from the publisher’s description: “It is now known that the more we understand pain, the less we will hurt.”

There have been a lot of misunderstandings about EP. Because explaining pain is tricky. (There are still plenty of unanswered scientific questions, too.) And because EP as a “brand” might be a bit of an over-hyped upstart, maybe given too much credit by too many people too soon — especially the idea that it actually reduces pain, which remains highly speculative. Nevertheless, for the record, here are some key misconceptions about EP …

• Explaining pain is not about managing or coping with pain. That’s another (important) kettle of fish.
• It’s not just about chronic pain. Acute pain needs splainin’ too.
• Explaining pain does not encourage people to move despite their pain — it’s just about teaching them that pain is often “overprotective.” Just because the brain worries too much sometimes doesn’t mean it’s always wrong.
• It’s not about the regulation of “pain messages” or “pain signals,” because there are no such things. It’s about the regulation of danger messages, and how only the brain can amplify or mute pain.
• The point is not to reassure people that pain is “just” a perception and not real (ugh) — it’s about reassuring people that the danger implied by pain may be exaggerated by the brain (or other dysfunction of the whole complex system).
• Many people seem to think that Explain Pain ignores biology, biomedical, and structural factors in pain. Nope: the point of explaining pain is to explain the “it’s complicated” relationship between those things and pain. Tissue damage is real, and pain arising from it is real, but they aren’t exactly in tidy sync with each other.46
• It’s not just about central sensitization (for which there is no known cure). Sensitization is an important sub-topic, but it’s important to explain unsensitized pain too.47 And the explain pain movement is actually rather optimistic (maybe even too optimistic) that learning the right things can actually change pain — even when it’s the product of sensitization.
• “Explain Pain” is not synonymous with “pain science.” The science of pain is the systematic investigation of the phenomenon and biology of pain; it isn’t a formal scientific field, but it is an area of research. Explain Pain is an approach to pain management inspired by new insight into how pain works.

But the mother of all misunderstandings is the popular idea that if pain is an output of the brain, then we must be able to think our way out of it. This is such an important and difficult topic that I’ve devoted a separate article to it: Mind Over Pain.

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That question was asked in a popular Facebook discussion group in early 2020. To be clear, it was not a reference to this website, but to ideas that are explored here (especially in this article), which are regularly mistaken for a treatment method (Explain Pain, either specifically or more generically).

That question attracted a lot of comments, but mine was rather popular, so I thought I’d transplant it to here, slightly edited and embellished for dramatic effect:

And what is “Pain Science” as opposed to the science of pain, exactly? Why capitalize it like a brand? What exactly are we talking about, if not “the science of pain”?

The owner of the domain PainScience.com (hint: it’s me) would really love to know what’s up with this capitalization bollocks. 😉 Because I know for damn sure that my brand is all about “the science of pain,” no capitalization, no modality or methology, no dogma or canon… just good information derived from the systematic investigation of the human experience of pain. That’s it.

If we are talking about the science of pain, then the question is effectively asking if clinicians are paralyzed by… knowing things. Are clinicians becoming paralyzed by the application of science to their work? By a modern and nuanced understanding of how pain works? Maybe they are!

But I’m sure that’s not a bad thing.

It’s true, knowledge can be paralyzing, and this has always been a challenge with evidence-based medicine: it’s hard! It’s the higher road. EBM is indeed harder than what came before. It is easier to just go with whatever witch’s brew of fact and fiction you’ve acquired from experience and mentors. Experience is especially seductive and misleading. But we do EBM not because it is easy, but because it is hard… and because it is better.

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There is no zealot like a convert, and some people get so entranced by the idea that pain is an output of the brain that they seem to deny that tissue state matters at all. If you’ve been frustrated by the advocates of Explain Pain and “pain science” on social media, this section is for you. Yes, sometimes they do go too far!

All pain is indeed completely generated by your brain, technically … but that is the nature of consciousness and perception. Most sensory experiences have strong roots in the world. Which includes the flesh.

Everything is in the brain, but when we want to learn about the universe, we look through telescopes, not brain scanners.

Dr. Rob Tarzwell of One-Minute Medical School. (Ironically, when Dr. Rob wants to learn about people, he looks at them with a brain scanner.)

If you want to know about nectarines, you mostly study nectarines, not the brains that perceive them. If you want to know about that nebula, you use a telescope, not a brain scanner. And if you want to know how back pain works, you are going to have to study back injuries and pathologies as well as the creative, colourful, and dysfunctional ways that brains play with perception of backs. But brains are still usually playing with the perception of something that is actually going on in the “world” of your back — in your tissues.

Photo by NASA on Unsplash

Is a nebula out there? Or is it just a mirage between your ears? Trick question!

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So, is pain a “sensation” and/or a “perception”? There’s a long-running debate/argument about this among pain science dorks and wonks on social media. The argument isn’t just about sensation versus perception, but also about whether it matters. Todd Hargrove tried to end the debate because he’s sick to death of it:

I tried for years not to write this post and ultimately failed. I’m sorry.

I don’t know what I like better: that he wrote it, or that he apologized for writing it. The whole thing has has gotten really tedious, and many people will groan when they see this zombie topic shambling their way yet again. Todd’s summary (which I entirely agree with):

1. The debate is not substantive or of practical import. It does not involve disagreements about pain physiology, what causes pain, or how pain should be treated. Instead, the debate is semantic.
2. The debate is easily resolved by simply looking at textbooks that describe how the terms sensation and perception are conventionally defined and used.
3. These textbooks make clear that it is completely appropriate to refer to pain as a perception, and it doesn’t make much sense to say that pain is a sensation but not a perception.
4. In any event, it doesn’t matter that much how we use these words in practice, because they are inherently fuzzy and often used interchangeably.

Good food for thought? More like food for not thinking about it ever again. But if you want to know about sensation and perception… he covers that too. Briefly. Which is all it ever needed.

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• “Pain really is in the mind, but not in the way you think,” Lorimer Moseley, TheConversation.com. In this not-too-technical article, the endlessly quotable Lorimer Moseley summarizes the role of the mind in chronic pain, especially low back pain.
• “Scratching an itch through the scalp to the brain,” Atul Gawande, NewYorker.com. This is a particularly wonderful article, which uses a fascinating and awful medical story — about a woman who scratched through her skull (seriously) — to explain how pain works, just as this article does. It’s a point that a lot of experts are making in a lot of different ways, and more all the time, but this is the best I’ve seen yet: great storytelling and superb reasoning, from Atul Gawande, one of the best medical writers alive today.
•  Why Things Hurt on YouTube.com. A genuinely funny and entertaining TED talk about a snake bite and pain neurology. No, really, you will actually laugh — it’s like stand-up comedy. A must-watch for anyone with chronic pain, and the professionals who care for them.
•  Understanding Pain and what to do about it in less than five minutes on YouTube.com. Beautifully produced short video that neatly summarizes most of the key points in this article. I do have a few quibbles with the treatment advice provided, however (discussed in Mind Over Pain).
• Pain: The science and culture of why we hurt (book), by Marni Jackson. Amazon.com ❐ Marni Jackson’s book is the perfect book for thoughtful, liberal, middle-aged women in pain who will probably thoroughly enjoy Jackon’s style. Others may find it frustrating, overtly poetical and coquettish, neither rigorous enough for the science-minded, nor explanatory enough for the layperson seeking real understanding of either “the science or the culture of why we hurt.” Nevertheless, it is one of the most accessible and modern surveys of pain science available to readers.
• 
  All in My Head: An epic quest to cure an unrelenting, totally unreasonable, and only slightly enlightening headache (book), by Paula Kamen. Amazon.com ❐ Like PainScience.com, this book offers an unusual combination of both humour and information about pain. Kamen is a completely engaging writer, and tells her story with both journalist rigour and personality.
• The Pain Chronicles: Cures, myths, mysteries, prayers, diaries, brain scan, healing & the science of suffering (book), by Melanie Thernstrom. Amazon.com ❐ Nicely summarized by Dr. Harriet Hall for ScienceBasedMedicine.org: “Melanie Thernstrom has written a superb book based on a historical, philosophical, and scientific review of pain. Herself a victim of chronic pain, she brings a personal perspective to the subject and also includes informative vignettes of doctors and patients she encountered at the many pain clinics she visited in her investigations. She shows that medical treatment of pain is suboptimal because most doctors have not yet incorporated recent scientific discoveries into their thinking, discoveries indicating that chronic pain is a disease in its own right, a state of pathological pain sensitivity.”
• A particularly excellent scientific paper by Lorimer Mosely: “Reconceptualising pain according to modern pain science”
• “Central sensitization: Implications for the diagnosis and treatment of pain,” Woolf, Pain, 2010. Pain itself often modifies the way the central nervous system works, so that a patient actually becomes more sensitive and gets more pain with less provocation. That sensitization is called “central sensitization” because it involves changes in the central nervous system (CNS) in particular — the brain and the spinal cord. Victims are not only more sensitive to things that should hurt, but also to ordinary touch and pressure as well. Their pain also “echoes,” fading more slowly than in other people. For a much more detailed summary of this paper, see Sensitization in Chronic Pain.
• Sensitive nervous system (book), by David Butler. Amazon.com ❐
• Explain Pain (book), by David Butler and Lorimer Moseley (book review). Amazon.com ❐
• Painful yarns (book), by Lorimer Moseley. Amazon.com ❐
• The Challenge of Pain (book), by Ronald Melzack and Patrick Wall. Amazon.com ❐
• “Gate Control Theory of Pain for Manual Therapists and Patients,” Nick Ng, www.massagefitnessmag.com. A detailed and accessible primer on gate control theory, with plenty of history and perspective too.