A History of Pain Science

By Rex Fujiwara and Timothy Marks

Old_book_bindings
It is commonly quoted that if we do not study history, we are doomed to repeat it; or, put another way, we can learn how to improve in the future by studying similar situations to our own from history. For instance, NFL teams have won the Super Bowl by studying films of the first half of the goal, and the stock market has historical patterns of rises and falls that can help analysts predict future trends.The same is true for healthcare, on both the patient and the clinician’s side.Chances are that, if you’re reading this, you’re a patient who’s been sent this article to read by your healthcare provider – and that you’re starting wonder why on earth the author is babbling on about history, and contemplating if your time wouldn’t be better spent going over to YouTube and watching some cat videos. The reason is this: Just as the NFL and stock market analysts review history to help them with their own jobs, it’s equally important that you understand the history of the study and science of pain. On the surface, you’d think pain is a simple thing – something ‘bad’ or traumatic happens to you, and your nerves send a message to your brain, which creates the sensation of pain. But in reality, pain is a very complex subject, and has been studied extensively for decades. In that time, our understanding of pain, and how you can affect it, has changed drastically.By way of yet another example, consider sugar and high-fructose corn syrup. Over the years, you’ve no doubt heard about how public opinion on these humble little sweeteners has changed. First, sugar was considered bad for you, and then everyone started bragging about how their stuff was sugar free and used high-fructose corn syrup instead, and then everyone started saying that was bad and started advertising how they had ‘all-natural sugar’, and then it turned out that enough of either of those things is bad for you, so really it doesn’t matter anyway.

On the off-chance that any of you reading this are dietitians or nutritionists, you’re likely rolling your eyes and muttering ‘duh’ right about now.

The point is, just as you can find arguments for either of those being a bad or good thing, the same is true for the science of pain. Even a casual search will reveal that a hundred different people will have a hundred different philosophies as to what causes pain, and more importantly, how to treat it. Unfortunately, all too often, people are content to espouse these methods and, when pressed on why they use them, only utter something along the lines of ‘it just works’. This is not good science, and it is not good medicine.

Studies have shown that by educating patients on why they are experiencing pain, their symptoms decrease much more quickly within a given time period as compared to patients who aren’t told about it. And as healthcare providers, it is our duty to provide a thorough analysis of pain, backed up by clinically proven evidence. Otherwise, if it turns out that your method is no better than a placebo, you could be doing literally anything and your pain would still be improving at the same rate. And who wants to waste their time and money on something like that? So that, to put it succinctly, is the purpose of this article – to give you an introduction to how the science of pain has changed over the years, and where it is at now.

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Before we begin in earnest, it is necessary to answer a very important question: What is pain? According to the International Association of the Study of Pain: “Pain is an unpleasant sensory and emotional situation, associated with actual or potential tissue damage, or described in terms of that damage.”

“But author!” You’re likely crying out. “I can feel this pain, as real as anything? How can you say that it’s emotional, or due to just potential damage, and not real?!” To this, I have a very simple reply: Just because it is not emotional does not mean it’s not real. To the average person, this might seem confusing, but there is a very important thing to understand before we can have any sort of discussion on pain.

The source of pain does not affect whether or not it is real.

Let me give you some examples. When you put your hand on a hot stove, sensors in your skin detect the sudden change in temperature, and activate a quick reaction to pull you hand away – long before the fibers and sensors that detect pain ever go off. Another example is a story told by one Lorimer Moseley, an author of some repute. While on a hiking adventure, he felt a scratch on his leg. He didn’t think anything about it, but ended up in the hospital because he was bitten by the second most deadliest snake in the world. He recovered from the injury and something interesting occurred when he went hiking again. While walking, he felt the same exact scratch on his leg, but this time he fell to the ground in agony. A friend went to his aide and was ready to call for help. He looked at his ankle and it turned out to be just a scratch.

So, obviously, this raises an interesting question. If the first time he felt nothing, why did he fall to the ground in agony the second time? The reason is very simple. When he was bitten by the snake, his body recorded the incident, noting that the bite there had serious consequences. When he was scratched, the body automatically had him spasm and curl up, in order to protect itself from another potential injury.

A third example is this. If you tickle a child for a long time, eventually they’ll get overloaded and cry for you to stop – and even if you wiggle your fingers without touching them, they’ll tense up, because the anticipation of the tickling creates an unpleasant sensation. Thus, they instinctively retreat to protect themselves.

The point of all three of the above examples is this: Pain is not only due to tissue damage. It may originate from the muscles and ligaments of your body, as well as the nerves and brain, working together, to create the sensation. As such, pain can come just as much from your nerves as it can originate from any part of the body – but it doesn’t make it any less real.

With that in mind, on with the article.

***

When dealing with science, the best place to start is at the very beginning. As I mentioned earlier, back then, and even today, people would try and treat pain, as well as other conditions, with a philosophy of ‘it just works’ without stopping to question why. And unfortunately, this can lead to people using methods that have negative side effects. Here are some quick examples:
One of the earliest treatments for a fever was bloodletting, or cutting someone and letting some of their blood drain out. This cooled off the patient, but we now understand that this is because blood loss causes a person to go into shock (a symptom of which is cold, clammy skin), not because it’s treating the fever.
In the past, cocaine was used as pain reliever, because when you touch it, it numbs the part of your body that it touches. Of course, now we know that cocaine is a highly addictive drug, with side effects such as panic attacks, paranoia, and increased likelihood of psychological disease.
Diet pills, along with other homeopathic treatments, are commonly sold today under the guise of allowing you to easily lose weight without having to change your lifestyle. To this day, not a single piece of reliable evidence that these actually work has ever been produced; however, by stating in the fine print that they’ve not been evaluated by the FDA, and that they work with ‘diet and exercise’ (which is what’s actually doing the work), the homeopathy industry is allowed to continue to sell them, largely unbothered.

By now, you’ve probably started to sense a pattern – a person describes a hypothesis (a proposed model for why something happens) for why pain occurs, and then later new evidence pops up showing that it doesn’t work like it was thought they did. The same thing has happened, throughout history, with the study of pain.

Among the first models created to explain why pain occurs was one created by Aristotle. He believed that pain was due to eeeeevil spirits, and that the gods entered your body during an injury. The brain was not believed to be involved at all, and instead the heart or liver was believed to be the center of pain control. (If you’re curious, Aristotle believed that the brain was actually a cooling system for the body – when you got a runny nose, it was because some of the coolant was leaking out.)

Later, in the 17th century, the scientist and philosopher Rene Descartes created the Cartesian Model of Pain. According to this model, pain is a stimulus created in your tissue at the origin of pain, and then those tissues send the pain messages to your brain. Under this model, the mind and the body were not considered to be connected to the production of pain. To put it another way, if you hit your foot with a 100 pound anvil, the brain will sense 100 pounds of pain (and you should probably check to make sure you didn’t wander onto the set of a Looney Tunes cartoon by accident). Or, put even more succinctly: Pain in a part of the body always means that the pain is coming from that part.

We now know that this theory is not complete, because if it was, treatments based around it (such as epidurals and cortisone shots) should always work – but sometimes, they don’t. The reason for this is because the Cartesian model does not consider that pain can occur for other reasons besides injury to an area; for instance, the body’s own protective mechanisms, heightened negative emotions such as stress or anxiety, or irritated and sensitive nerves can all cause you to feel pain.

In 1965, a couple of guys named Robert Melzack and Patrick Wall realized just that, and, to take that into account, created what’s known as the Gate Control Theory of Pain. In this theory, the spinal cord – the place where all of the nerves in the rest of your body join to go to the brain – acts as a gate of sorts, sending noxious and non-noxious messages to the brain. (If you’re wondering what noxious means, it’s just a five-dollar word for “a stimulus that is damaging, or threatens damage to, normal tissue.” Remember the definition we gave for pain earlier in the article.) To go back to the example with the anvil, when it gets dropped on your foot, your brain will receive that noxious stimulus. Since you’ve wandered onto the set of a Looney Tunes cartoon, thankfully your foot is intact (if a bit flattened by the impact); however, it is rather painful, and so you start hopping around and rubbing it in pain while making a hilarious howling noise. When you rub your foot, the spinal cord interprets this as a positive, non-noxious stimulus, which “blocks” some of the noxious stimulus from the anvil injury. Another example is when a kid scrapes his/her knee and we ‘kiss it better’ – the non-noxious stimulus from the comforting gesture blocks the noxious one from the scrape. This theory is the basis for what we call electrical stimulation or TENS units; pain decreases while we apply the electrical current (because it’s blocking out the painful stimulus), but it gradually comes back afterwards.’

Even with the new model, however, Melzack knew that there were still some things it couldn’t explain, one of the biggest being what’s called Phantom Limb. In phantom limb pain, people who have had amputations (such as with a leg or arm) will sometimes report feeling pain in that limb, even though it’s no longer there. How is this possible? It all goes back to the concept of the memory of pain; just like Moseley had the memory of the snakebite to make his scratch painful, so the amputee’s memories of whatever caused the amputation provoke pain where they think the limb should be.

To try and account for that, Melzack created a new model for pain, the Neuromatrix model, in 2001, and then updated it with help from Katz in 2013. It’s the most recent, up-to-date explanation of pain currently out there, and it’s also hilariously complicated, so we’re not going to go over in-depth. Here is a diagram in case you are curious about it:

However, with a bit of work, we can whittle it down to the important bits. First, we need to understand the Three Things that affect your Nervous System when there is an injury/potential injury.
1.Cognition, which covers both your instinctive and learned knowledge of pain. This includes memories of past experiences, your attention to an injury, and your body’s perception of pain.
2.Your Sensory Systems. This includes input into the body from the skin and from the joints, internal organs, and miscellany.
3.And lastly, there’s the Emotional side of pain. This includes things such as anxiety, blood pressure, and other automatic responses.

Whenever you experience pain, these three things go into what’s called the pain neuromatrix, which is a mental construct that acts like a monitoring system for the body. It then takes those three things and mashes them together to create the perception of pain, an action plan to respond to it, and changes to how your body controls stress.

For an example, let’s go back again to the story about Moseley. The first time, he wasn’t really paying attention to the bite, and he had no memory of severe injury there. Since the bite itself wasn’t really that painful, he didn’t feel anything until he started getting clammy and had to be taken to the hospital. The second time, however, the memory of that bite set off alarm bells in the body, and it triggered stress responses and severe pain to try to protect itself.

***

So at this point you’ve likely started to get bored again, and are probably wondering “How on earth is any of this relevant?” The answer is very simple. By understanding that there are different things responsible for us experiencing pain, we can look at each possible factor. For instance, if you have low back pain, it means that we need to look, not only at something physically being wrong with your back, but also at the other two things that contribute to the neuromatrix.

So, by understanding that there are many components that contribute to the pain process, we can look at each possible factor. What this means is that the low back pain that many may experience for years may not be only due to a “back problem”, it may be more related to other components of the neuromatrix. More importantly, it means that, as far as we’re concerned when treating your pain, the mind and the body are equally responsible. To go back to the words in bold up above, The source of pain does not affect whether or not it is real.

Is your pain because you had an injury? Yes, it can be.

Is it because there are changes in your nervous system? Yes, because without nerves, you couldn’t feel any pain.

It is because of your brain? Yes, because your brain is responsible for taking the input and turning it into the sensation of pain in the first place.

By now, you’re probably sick of me going on like a broken record, but it is really important to hammer this home. Pain is always real. It is the thing that’s causing it that we can’t always quite get to the bottom of. That’s why, when you come in for treatment, we do all of the exams and give you all those movement exercises and manual therapy– it’s to try and suss out what’s related to it and focus our efforts there.

With all of that said, there’s just one final question. How does this affect you? Because we’ve talked about this, because you’ve stuck around and read through to the end, you now know that pain can be influenced by any number of things. The injury, the nerves, the brain, stress, worry, bodily protective mechanisms – all of these may or may not be contributing. So by knowing this, you can now go into this with an open mind, and give yourself a chance to try new things to improve your pain – and more importantly, to take control of it.

And as GI Joe said, knowing is half the battle.

***

Before I sign off for good, however, I’d just like to speak briefly to any healthcare professionals who might be reading. (If you’re a patient, feel free to go ahead and do something else.) By reading this, you should be taking away a lesson of your own: The reason your patient is experiencing pain may or may not be what you think, and the same thing applies to when they improve. Just think about the whole bloodletting example; just because symptoms get better doesn’t mean you’re treating the cause.

So if someone experiences knee pain, there are two main scenarios.

1. We tell them the problem is the knee. This can lead to catastrophization (stress and worry) that there is a problem with the knee which can lead to more pain.

2. We can educate our patients and clients that pain can increase due to the numerous possible factors that have the potential to improve. This may decrease catastrophization and promote a positive outcome. This is explained in the following sections and here is a preview:

Findings from X-rays, MRIs and CT scans will find problems in the body, but it may or may not be related to your pain.

Stress and worrying about pain can increase and magnify pain.

Pain can increase due to the trigger of a memory of pain.

As clinicians we must keep up the good work we are currently doing by helping our patients and clients understand and take control of their painful experiences to regain function. Let’s improve our explanatory model of why our patients improve to further enhance our patient’s progress.

Also, there are many in depth articles about the neuromatrix model of pain. Just do an online search.

Diane Jacobs, a physical therapist and educator practicing in Canada has written detailed explanations of the neuromatrix model on her blog.

Laurence Bradley, a professor of medicine at the University of Alabama has written an article about the neuromatrix model for the Journal of Rheumatology.

Joseph Brence a physical therapist and research has written about the neuromatrix model on his blog as well. He has won an award for best research blog for physical therapists in 2014!

References:

Photo: https://upload.wikimedia.org/wikipedia/commons/8/87/Old_book_bindings.jpg

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Forrest CB, Shi L, von Schrader S, Ng J. Managed care, primary care, and the patient-practitioner relationship. J Gen Intern Med. 2002 Apr;17(4):270-7.

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Vetter TR, McGwin G Jr, Bridgewater CL, Madan-Swain A, Ascherman LI. Validation and clinical application of a biopsychosocial model of pain intensity and functional disability in patients with a pediatric chronic pain condition referred to a subspecialty clinic. Pain Res Treat. 2013;2013:143292. doi: 10.1155/2013/143292. Epub 2013 Oct 22. PubMed PMID: 24251035; PubMed Central PMCID: PMC3819919. Free full text

One comment

  1. […] One of the most common reasons stretching is performed is to increase flexibility. Have researchers found that stretching improves flexibility for everyone? This might seem like a silly question,  but it is an important one because there are many things we have done in the health field that have been incorrect. Read here about the history of pain science to understand what I mean. […]

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