Have you ever been told by a practitioner that pain is “in your head”? Or maybe you’ve been told your pain is “chronic” and that’s just the way it’s going to be from now on. Maybe you haven’t had either experience, but you worry that pain with aging is inevitable, so you assume and worry that you’ll develop chronic pain.
This article will give a general overview on what pain is, what defines chronic pain, and what research suggests for managing chronic pain.
What is Pain?
The Institute for Chronic Pain (ICP) is “an educational and public policy think tank whose mission is to make pain management more effective by changing the culture of how chronic pain is treated.”1
The ICP defines pain as “a sensory and emotional experience associated with, or resembling that association with, actual or potential tissue damage.”1
At first read, this may seem odd, right? Why is pain considered an “emotional” experience?
According to the article on the ICP website, we can likely acknowledge that pain is sensory because we experience the sharp poke of a needle, the joint stiffness of arthritis, or the ache of low back pain.
If we actually think about it, we also experience pain associated with emotions. The example they give is children getting a belly ache the night before the first day of school. Or think about how your body feels when you’re excited about something- the emotions of fear and excitement generate sensations in our bodies as well.1
Why Does “Potential” Tissue Damage Cause Pain?
According to ICP, pain is like an alarm system within our bodies. When an alarm sounds, we react to avoid any harm.
“Fire alarms alert us to something that is going wrong in the building and we reflexively react with avoidance behaviors — we get out of the building.”1
This is where the “potential” tissue damage idea comes in. When our pain alarm sounds, we react so that we don’t get seriously hurt (even though we haven’t been hurt yet).
Similarly, when movement has caused pain before, the brain may sound the alarm when we attempt to do a certain activity.
Let’s Look Where Pain is Interpreted in the Brain
Pain is a product of the central nervous system, meaning the brain and the spinal cord.1
Brain activity occurs in different regions when pain occurs.
First, pain lights up the somatosensory part of the brain, which is responsible for identifying the type of pain, or the sensation. If your pain is sharp versus dull, for example.1
The limbic system is also important with pain processing, which is responsible for emotional regulation and response. The limbic system is particularly active when it comes to survival. So our “flight, fight, or freeze” response is controlled by the limbic system.1,4
This helps to explain why pain is not just a physical but also an emotional process.
Pain Theories
There are two primary pain models or theories that are utilized in the world of chronic pain- the gate control theory and the neuromatrix theory.1
For some people the word “theory” brings to mind fables. It’s important to remember that in science, a theory is based on the scientific method and supported by a lot of evidence. Einstein’s theory of relativity is another example of a theory. So, don’t let the word throw you off, theses theories are widely utilized in scientific research and the medical world.
The gate control theory was created by Dr. Paul Melzack and Dr. Patrick Wall, and the neuromatrix theory was later created by Dr. Paul Melzack.1
Gate Control Theory of Pain
We have different nerve types in our body. Nerves that travel away from the central nervous system (efferent) and nerves that travel towards the central nervous system (afferent).
The nerve fibers that carry pain information are different than the nerves that carry information about touch, vibration, and pressure. The fibers that carry touch, vibration, and pressure (called “non-nociceptive” fibers) are larger than the ones that carry pain.2
Although the fiber types are different, they bring their signals to the same two sites in the spinal cord. These sites are the transmission cells which carry information to the brain or inhibitory cells, which decrease the impact of transmission cell activity.2
To best illustrate how the gate control theory works, let’s use an example.
Imagine you just smashed your finger in a cabinet door (accidentally, of course). It’s likely that your first reaction is to start shaking your hand or may even put pressure on it (maybe while using shouting a few choice words).
If our finger is already hurting? Why would we move it or apply pressure? The answer is the gate control theory.
In this case, the pain nerves deliver information to transmission cells to be taken up to the brain that say “Holy cow that hurt!” At the same time, that hand shaking is carried by the non-nociceptive fibers that are larger than the pain fibers. So they cause the inhibitory cells to fire, which impedes the transmission cells.
Of course, pain is not immediately alleviated because of the shaking/pressure, but it actually does help to lessen in.
A clinical example would be the TENS unit or electrical stimulation machine. With these devices, clients feel a tingly sensation wherever the electrode pads are placed. What this is doing is utilizing the gate control theory by applying a non-nociceptive stimulus (electricity/vibrations) to activate inhibitory cells in the spinal cord. This lessens the intensity of the transmission cells and therefore, the intensity of the the pain is decreased.
Cartesian Pain Theory
Okay, so if you’ve been reading carefully, this pain theory hasn’t been mentioned yet. That’s because in the pain science world, it’s not widely accepted anymore to explain chronic pain.
However, some practitioners still utilize this theory and Dr. Melzack’s neuromatrix theory directly challenges the cartesian theory, so it’s important to understand.
The philosopher Rene Descartes created the cartesian model .1
Descartes’ theory posits that when tissue is damaged nociceptive (pain nerve signals) are sent to the spinal cord and the brain and the tissue damage is interpreted as pain.1
In many ways, this theory seems like common sense, because we know when we just smashed our finger in the cabinet, and our tissue was damaged, there was pain.1
Inaccuracy of the Cartesian Pain Theory
What Melzack noticed was that the cartesian theory didn’t explain things like phantom limb pain.1
Phantom limb pain can occur in those who’ve had an amputation. For example, I had a patient who had a foot amputated, yet he still reported feeling pain in his foot.
The pain these individuals experience is very real and can be extreme.
If pain is based on tissue damage, however, it doesn’t make sense that phantom limb pain can exist because there’s no damaged foot to send the signal to the brain.1
Additionally, research on tissue damage as it relates to pain intensity indicates the severity of tissue damage doesn’t correlate to pain levels.1
Additionally, research on tissue damage as it relates to pain intensity indicates the severity of tissue damage doesn’t correlate to pain levels.
A study done in 2015 looked at over 3,000 individuals who had no back pain and who underwent MRIs of the spine. Those who had a disk bulge on their MRI increased from 30% of those in their 20’s to 84% of those in their 80’s.3 Even though a disk bulge would indicate tissue “damage” these individuals had no pain.
Meanwhile, there are some people who experience high levels of pain, yet imaging reveals no tissue damage. It seems like the brain plays a bigger role than just receiving pain signals.
That brings us to the neuromatrix theory of pain.
The Neuromatrix Theory of Pain
The neuromatrix theory of pain holds two main beliefs that are counter to the cartesian model and previously held beliefs about pain.
- “Pain is created in the brain and spinal cord, not due to tissue damage.
- Multiple parts of the central nervous system work together, in response to signals from the peripheral nervous system, to produce the experience of pain.”1
What Melzack recognized is that the brain and spinal cord don’t just receive the signals of pain, the brain and spinal cord create them. This helps to explain why the amount of tissue damage doesn’t equate to the intensity of pain one experiences.1
While this theory may seem harder to wrap our minds around, understanding the difference between acute pain and chronic pain syndrome can help.
First, let’s look at the role of the peripheral nervous system in delivering messages surrounding noxious stimuli.
Nociception
A noxious stimuli is something that has the potential to cause damage tissue. Examples include intense heat, a paper cut, falling on the ground, etc.
Noxious stimuli travel on those sensory neurons discussed above. These sensory neurons live in the peripheral nervous system and deliver messages to the central nervous system.
Nociception is the process of encoding noxious stimuli. As the International Association for the Study of Pain (IASP) points out, not all noxious stimuli trigger pain. For example, feeling intense heat may cause you to pull your hand away from the oven, but you don’t actually feel pain.5
The best example I have for this is when I was in physical therapy school and we had a guest lecturer. Our guest was a PhD candidate who was discussing his thesis project with us. After talking for about an hour, he gave us a break. I hastily stood up and attempted to walk out the door, toward the restroom, when my boot caught a chair behind me and I plummeted (in what felt like incredibly slow motion) to the floor. My phone went flying across the room and I landed with not only a loud thud, but the crash of multiple chairs. Needless to say, everyone (including our guest lecturer) was staring.
While the hard floor was definitely a noxious stimuli, my brain’s message wasn’t “Ouch! Pain!” it was “Get up quick, this is embarrassing!”
I truly don’t remember having any pain from that experience, although I probably did bruise, because the noxious stimuli didn’t trigger a pain response.
Nociceptive Pain
As we all know from experiencing a stubbed toe or paper cut, noxious stimuli can indeed trigger a pain response.
Nociceptive pain is defined as “Pain that arises from actual or threatened damage to non-neural tissue and is due to the activation of nociceptors.”5
This type of pain occurs when the central nervous system is responding “normally.” When someone experiences acute pain this response is generally typical.
When someone is experiencing chronic pain syndrome, however, the central nervous system, or the body’s alarm system isn’t working correctly.
This means that an individual with chronic pain syndrome may be experiencing nociceptive pain and/or may also be experiencing other types of pain generated from the brain.
One example is nociplastic pain, which is defined as “Pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain.”5
This goes back to the idea of the neuromatrix of pain theory- tissue damage doesn’t have to be present for pain to exist.
Acute Pain Vs. Chronic Pain
When it comes to acute versus chronic, it’s often explained as acute is more recent (within the last 2-3 weeks) and chronic is long-lasting (like 6 months or more).
This is often how practitioners (myself included, prior to doing research for this article) described and treated chronic pain. Basically, if it was lasting more than 6 months, I would explain to my clients that the tissue was no longer damaged, so while pain was still there, no harm was being done.
While that’s true, it likely wasn’t the most helpful. At the end of the day, it likely just made my client feel powerless or maybe even confused about the source of their pain.
Central Sensitization
One of the facilitators of developing and maintaining chronic pain is central sensitization.
Central sensitization means that the nervous system is consistently on high alert, or what’s called going through “wind-up.” Basically, the threshold for what’s considered painful is lowered, so stimuli that weren’t previously painful can be and pain is maintained after tissues are healed.
During central sensitization, two main things occur:
- Allodynia– when previously non-painful stimuli (like soft touch) is perceived by the brain as painful.
- Hyperalgesia– when previously painful stimuli (like stubbing your toe) is perceived as even more painful.
Since the nervous system is in such a heightened state, those experiencing central sensitization may experience greater sensitivities in all senses, like light and smell.1
Also, this condition corresponds with “heightened levels of emotional distress.” This, of course, is understandable as the nervous system is not only responsible for physical, but also emotional responses.1
If you can imagine experiencing this, you likely understand how those with central sensitization can start to feel “crazy.” While they intuitively know the washcloth they use to wash their face shouldn’t cause pain, they can’t use it anymore because it’s too painful.
It’s essential to remember that those with chronic pain and central sensitization are not “crazy” nor did they cause their pain.
Chronic Pain Syndrome
Illness or injury typically causes chronic pain. For it to be “chronic” the pain usually has persisted for 6 months or more.
Over time, the pain can cause additional symptoms, which impact the body, nervous system, and overall quality of life.
Chronic pain syndrome is a combination of chronic pain and additional symptoms or ” secondary complications.”1
Secondary Complications of Chronic Pain
Secondary complications may include:
- Difficulty sleeping
- Irritability
- Stress
- Inability to maintain employment
What tends to happen with secondary complications is that they contribute to a vicious pain cycle.1
Take a look at this example from the ICP:
“Many people tend to have trouble sleeping because of pain. After a while, they are so tired and their patience has worn so thin that everything starts bugging them. They also find that coping with chronic pain gets harder and harder too.
Some people stop working. With the job loss, they might come to experience financial problems. The stress of these problems keeps them up at night. Thinking too much in the middle of the night can make the original sleeping problem even worse. It can be hard to shut off the thinking even in the middle day.
Chronic pain can also affect the roles people have in the family. They miss out on children’s activities, family functions, and parties with friends. As a result, many people struggle with guilt. Guilt isn’t the only emotion that is common to living with chronic pain. Patients tend to report some combination of fear, irritability, anxiety and depression. Patients also tend to express that they have lost their sense of direction to life.
They are stuck. These problems are all common when living with chronic pain.”1
You can imagine how this cycle may feel almost impossible to stop. Chronic pain syndrome invades one’s entire life, so it’s vital that people living with chronic pain and chronic pain syndrome find the help they need.
Chronic Pain and the Healthcare System
In the medical field, we often talk about “chronic conditions.” Examples include diabetes, heart disease, and cancer.
As the ICP aptly points out, medical professionals treat patients with those types of conditions in a certain way. More specifically, medical professionals encourage utilizing lifestyle changes to help the symptoms of their condition, improve quality of life, and decrease pain/burden associated with their condition.
For people with chronic conditions, there may not be a cure, per se, but there’s options for what they can do to improve their health and well-being.
The difference is individuals who are experiencing chronic pain is that they’re led to believe that their condition can be cured. So they often are put through a variety of procedures and tests, looking for the cause or where the tissue damage is. Or they may even be told surgery can resolve their pain.
“Research has shown that surgical and pharmacological intervention are largely ineffective or minimally effective.”1
The ICP (understandably) believes this approach is a failing of the healthcare system. Managing chronic pain, like other chronic conditions, isn’t about finding a cure. Rather, people with chronic pain can learn self-management strategies to help improve symptoms and quality of life.
“Studies have found chronic pain rehabilitation to be the most effective for chronic pain, particularly when compared to narcotics and surgical intervention.”1
Resources for People with Chronic Pain
American Chronic Pain Association Rehabilitation Programs
Mayo Clinic Pain Rehabilitation Center
Resources from the International Association for the Study of Pain
Have the Strength to Live Life to the Fullest!
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Sources:
- McAllister, M. (2022). What is Pain?. Retrieved 4 May 2022, from https://www.instituteforchronicpain.org/understanding-chronic-pain/what-is-chronic-pain/what-is-pain
- Gate control theory – Wikipedia. (2022). Retrieved 4 May 2022, from https://en.wikipedia.org/wiki/Gate_control_theory
- Brinjikji, W., Luetmer, P. H., Comstock, B., Bresnahan, B. W., Chen, L. E., Deyo, R. A., Halabi, S., Turner, J. A., Avins, A. L., James, K., Wald, J. T., Kallmes, D. F., & Jarvik, J. G. (2015). Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. AJNR. American journal of neuroradiology, 36(4), 811–816. https://doi.org/10.3174/ajnr.A4173
- The limbic system. Retrieved 4 May 2022, from https://qbi.uq.edu.au/brain/brain-anatomy/limbic-system#:~:text=The%20limbic%20system%20is%20the,and%20fight%20or%20flight%20responses.
- Terminology | International Association for the Study of Pain. (2021). Retrieved 4 May 2022, from https://www.iasp-pain.org/resources/terminology/
