A History of Pain Science

Main Points
1. There are many theories explaining the pain process.
2. The pain process involves many components that can be treated including sensation, perception, injury, sensitivity of nerves, the brain, stress, anxiety, and etc.
3. We have the potential to improve.
Estimated time to read 12 min (1900 words)

History is not only about the study of the past, it can also be a lesson for the future. For example, NFL footballs team have won the Superbowl based on studying the film of the first half of the game. Politicians can deal with the economy  based on historical situations. The stock market has historical patterns of bull and bear market patterns that may help predict future trends.

Learning about the history of pain science is just as important because what we know as truths can change with research. Have you heard that eggs are not good for you, then reports indicated that eggs were not as bad as initially thought? The same with coffee. You can find arguments for both sides. The same is true for the science of pain. We need to study the past as well as newer research to optimize our treatment to make sure we are practicing using proven methods and not harming patients.

There are many theories involved with the treatment of painful conditions, Unfortunately, some have become part of a belief system which becomes very difficult to challenge and question. But we must! For clinicians viewing this website, please understand that treatment philosophies should not be based on beliefs, but should be based on sound research that we should freely be able to challenge and deconstruct. Additionally, we shouldn’t take it personal if someone disagrees with an explanation of treatment.

What I find interesting is that I often hear that many clinicians do things because their treatments work without trying to understand why it works. This can lead to problems.

In the past, one of the first treatments for fever was bloodletting, which is to simply let the person bleed. We now know that that bloodletting a person would reduce a fever because someone who is bleeding can go into shock and one sign of sock is cold clammy skin.

Heroin was regularly used in cough syrups and we now know that it is a very addictive.

Frontal lobotomies (removal of parts of the brain) were performed in the 1940s and 1950s for people with psychological disorders. We now know that destroying parts of the brain is detrimental to function.

There are may theories within pain science that have been developed and refuted.

One of the first pain theories involved Homer (8th century BC) who described pain as “arrows shot by Gods”. Aristotle (384 BC – 322 BC) stated that Pain was due to evil spirits and that the gods entered the body during injury. The brain was not believed to have any direct influence and for years the liver or heart was considered to be the center for pain control. Many cultures and societies have developed their own theories regarding pain, including causations from deities, energy fields, the moon, and the stars.

Rene Decartes (1596 – 1650),  the father of the Cartesian Model of Pain described pain as a stimulus created by the tissues as the origin of pain and the tissues send pain messages to the brain. The mind and the body were not considered to be connected to process pain. If you hit your foot with a 10 pound hammer, the brain will sense 10 pounds of pain. Based on the Cartesian Model, pain in the foot means that pain comes from the foot all the time. Examples of treatments that are based on the Cartesian Model of pain include epidurals, other types of nerve blocks, and cortisone injections.

We now know that this theory is not complete. If pain always originates from the body part that is injured, these treatments just mentioned should always work.  The lack of success is due in part because the Cartesian Model does not consider that pain can also be due to protective mechanisms, emotions, or sensitivity of the nervous system.

A second issue with the Cartesian Model is that nerves do not send pain messages. Nerves send and receive chemical messages from one site to another that results into the sensation and perception of pain.

So where does pain come from?

In 1965, Ronald Melzack and Patrick Wall (1925-2001) created the Gate Control Theory of Pain. They understood that the Cartesian Model of Pain was not complete so they created a new theory.  In this theory, the spinal cord is the gate that sends noxious and non-noxious messages to the brain. (A noxious message is defined as a stimulus that is damaging or threatens damage to normal tissues. Remember that pain can increase due to actual or potential tissue damage. You can review the definition of pain here). If there is a noxious stimulus such as getting your knee hit by a 10 pound hammer, the brain will receive that stimulus. If you rub your knee, the spinal cord will receive this as a positive (non-noxious) stimulus, which will block some of the noxious stimulus that may be effecting pain. Another example of this is a child falling down and crying, when we kiss his or her knee, it feels better. Electrical stimulation or TENS units were created based on the Gate Theory of Pain. Pain may decrease while the stimulation was on, but would often return after the effects of the stimulation decreased.

Ronald Melzack knew that the Gate Control Theory was not complete because he felt that it does not explain various conditions including phantom limb pain. (WebMD has information about phantom limb pain here.)  How is it possible to experience pain in the leg even after it is amputated? This may be due to continued noxious stimulation from the nerves that have been severed. It may also be due to modulation from the brain. Is there a memory pathway within the nervous system? Is it associated with emotions, movements, hormones, autoimmune system, or inflammation?

In 2001 Ronald Melzack described the Neuromatrix Model of Pain, which was updated together with Joel Katz in 2013. The Neuromatrix Model of Pain is an attempt to include all concepts of pain found in current research at that time.

Here is a diagram of the Neuromatrix Model of Pain:

The three items below play a role within the nervous system when there is an injury or potential injury.

1. Cognition: memories of past experiences, attention, meaning of pain, anxiety

2. Sensory System:  input into the body from the skin and within the body (joints, internal organs, etc.) due to injury or potential injury

3. Emotion: stress mechanisms,  blood pressure, and other automatic processes

The entire body consists of a pain neuromatrix, which is a “body-self matrix” that analyzes cognition, the sensory system and emotional components to create an output to parts of the brain to create pain perception, an action plan or pattern to respond to pain, and changes in stress regulation.

Lorimer Moseley, a physical therapist and researcher has an example in his book Painful Yarns.

While hiking, he felt a scratch on his leg, previous memories of his leg scratched were not significant. There was minimal cognitive attention, anxiety or emotional connection to the scratch. Nerves on the skin sends the message of the scratch to the spinal cord then up to the brain. There was minimal pain because in prior experience, simple scratches are not significant. There is minimal change in stress, blood pressure or other automatic processes. But what he did not know was that he was bit by the second most deadliest snake in the world leading to hospitalization.

He recovered and while hiking sometime later, he felt that same exact scratch on his leg. The input to the brain triggered the memory of the previous incident and the meaning of the scratch was completely different. His brain associated the scratch with potential injury which can increase anxiety. There was increased stress, blood pressure and automatic processes to turn on protective mechanisms within the body. Pain is then created as an output of the brain with an action involving falling to the ground and taking a look at his ankle. There is increased stress response to force him to deal with the scratch. When he looked at the scratch, it was nothing. It was simply a scratch from a bush.

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 low back pain that many experience for years may not be only be due to a back problem, it may be also related to other components of the neuromatrix such as fear of pain / movement, stress, depression, or anxiety.

There are many in-depth articles about the neuromatrix model of pain that can be found online. Here are a few sites in case you are interested in more reading:

Diane Jacobs, a physical therapist and educator practicing in Canada has written detailed explanations of the neuromatrix model  in 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!

Another concept involved with the science of pain includes a “sensitive nervous system” by David Butler. Nerves associated with injury become sensitive and can trigger a painful sensation more easily. For example, lightly touching a bruise can be very painful right after an injury even though it will not cause further tissue damage. After a short time, the sensitivity diminishes while the bruise is still present but touching the bruise is no longer painful. An issue that may occur is when the bruise or injury is healed but there is continued sensitivity resulting in continued pain due to “misfiring” of nerves. This may be one reason people experience phantom limb pain.

David Butler also explains that the central nervous system may become sensitive. There are changes within the brain that may trigger painful responses and pain may be associated with memories, emotion, stress, or anxiety.

What this means is that the body and the mind cannot be separated when treating a person experiencing pain. This can also be described as the Biopsychosocial Model that was introduced by Dr. George Engel in the 1970s.

We must give ourselves the opportunity to treat or improve every aspect of the pain process. So we should ask ourselves these questions:

Is pain a direct result from an injury? yes

Is pain due to changes in the nervous system? Yes, our nerves may become “more sensitive” and may send messages of injury or potential injury triggering a pain sensation.

Is pain modulated by the brain (central nervous system)? yes, pain levels can depend on the status of multiple factors that can affect chemicals in the brain.

This does not mean the pain is in the head or made up. It is real. Pain is always real, it is the mechanism of pain that researchers are slowly figuring out. So let’s try to be positive and continue movement exercises to give the body and brain the opportunity to change for the better.

If we experience chronic pain in any part of our body, we know that pain can be influenced by many sources; it can be due to the injured site, autoimmune, sensitivity of the nervous system, stress, worry, anxiety, and etc. It also gives us the opportunity to work on different treatments from health care professionals to give our body an opportunity to improve.

References:

Engel GL. The need for a new medical model: a challenge for biomedicine. Science. 1977 Apr 8;196(4286):129-36. PubMed PMID: 847460

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.

Pettman E. A history of manipulative therapy. J Man Manip Ther. 2007;15(3):165-74. PubMed PMID: 19066664; PubMed Central PMCID: PMC2565620. Free full text

Woolf CR, Rosenberg A. The cough suppressant effect of heroin and codeine: a controlled clinical study. Can Med Assoc J. 1962 May 5;86:810-2. PubMed PMID: 14008278; PubMed Central PMCID: PMC1849153. Free full text

Braslow J. Therapeutic effectiveness and social context: the case of lobotomy in a California state hospital, 1947-1954. West J Med. 1999 May;170(5):293-6. Review. PubMed PMID: 10379224; PubMed Central PMCID: PMC1305592.Free full text

Lindau ST, Laumann EO, Levinson W, Waite LJ. Synthesis of scientific disciplines in pursuit of health: the Interactive Biopsychosocial Model. Perspect Biol Med. 2003 Summer;46(3 Suppl):S74-86. Review. PubMed PMID: 14563076; PubMed Central PMCID: PMC1201376. Free full text

Melzack R & Wall PD. Pain mechanisms: a new theory. Science. 1965 Nov 19;150(3699):971-9. Review. PubMed PMID: 5320816

Melzack R. Pain and the neuromatrix in the brain. J Dent Educ. 2001 Dec;65(12):1378-82. PubMed PMID: 11780656

Melzack R & Katz J. Pain. WIREs Cogn Sci 2013, 4:1–15.

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

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