03 Nov What is Pain? Part 1 of 3
Pain is a qualia and an enigma; it’s a sensation that is routinely described yet not fully understood. The mystery lies in that pain is an experience felt by almost all individuals at some point in their lives, however, the experience of this universal sensation remains individualized and unique to that person. What is pain? Why do we have pain? How far has pain science research come? Is pain a good or a bad thing? Can we combat the high and rising rates of chronic pain and the opioid epidemic? Find out in this series of articles!
What is Pain?
Why is it so hard to understand and explain something that almost everyone experiences? Well, to understand where we are now with pain concepts/theories, we have to understand and honor where we used to be. The modern theories could not be developed without the older theories. These theories were not completely inaccurate, however, they were incomplete. As technology has advanced so has scientific findings. In other words, get ready for a quick history lesson on previous theories and their shortcomings that will allow us to answer, what is pain?
Theories of Pain
There have been many pain theories proposed, the first ideas of pain were formulated before 1800. In Chinese medicine pain appeared for the first time in the ancient book Huang Di Nei Jing (The Yellow Emperor’s Classic of Internal Medicine), westerners first saw pain descriptions appear in the Iliad and the Odyssey. Prior to the Renaissance, the heart was considered to be the home for our emotional and mental functions. Galen (130-201 BC) proposed the brain is the site of feeling. This was followed up by Rene Descartes, who described the transmission of pain information through peripheral mechanisms, to the spinal cord, and then to the pineal gland of the brain. He gave us the famous drawing shown below:
Descartes was responsible for the Cartesian Dualistic theory, a very complex, often confused, and misunderstood theory. Basically, Descartes’s dualism refers to defining the body and soul as two distinct substances but are intermingled. The symptoms of pain were described as one of the primary experiences which test the existence of the body vs spirit. If interested in obtaining the classic mental pretzel of this theory, readers are referred here. Descartes’ work along with other theories set the stage for further concepts in the 1800s.
There have been many pain theories proposed, we will focus our attention on the most influential while also answering common questions related to pain.
Traditional Views of Pain: Is there a specific hardwired neural pathway for pain?
The first theory we need to acknowledge is the Specificity theory, proposed in 1811 and credited to Charles Bell. Fun fact, Charles described this theory in a book that was privately circulated amongst his peers. However, Avicenna may be the first to describe pain as an independent sensation from touch or temperature. Regardless of the initial creator, the theory states we have specific receptors associated with a specific stimulus that goes to a specific area of the brain, see how it got its specific name, See more here: (Moayedi and Davis 2013)
This theory also viewed the brain as a complex structure vs a homogenous object. Side note; this becomes true with a lot of modern-day theories.
For example, posture used to be viewed as the ideal position using a plumb line and that we should all be standing or sitting similarly. The old school of thought was that if we stray from this line, we will be in pain and agony, however, this idea has not been supported. Check out this video that talks all about exactly what is ‘postural pain’ and what you can do for it!
As technology and science advanced many researchers contributed to this theory (see Bell-Magendie Law) and (law of specific nerve energies). Additionally, work by Mortiz-Schiff and Edouard Brown-Sequard showed differing pathways along the spinal cord for temperature and pain compared to light touch. Lastly, Sir Charles Scott Sherrington added in the finding of the nociceptor. This was a major component lacking from the specificity theory. Simply stated, in order to have a specific pain pathway there must be sensory organs or fibers that are dedicated to inflammation or damage in that particular tissue. Furthermore, he was able to show that in the presence of noxious stimuli a withdrawal reflexed occurred. To this point, pain was thought to occur along a specific pathway, where the nociceptors would send information of potential threat or damage causing the body to withdrawal away from the stimulus. Seems like a pretty good theory right? Yes, but it was not complete. The theory failed to describe how pain could still be experienced after healing had occurred. For example, tendon injuries typically take 6-8 weeks to heal biologically, yet people can experience tendon related pain long after the biological healing has occurred. Learn more about healing times below! Furthermore, it could not explain how a patient with an amputation could be experiencing phantom limb pain.
Specific Theory Shortcomings On What Is Pain
This also helps to explain the shortcomings of our next theory; the Intensity theory.
Do we feel pain because of the intensity of the noxious stimulus?
Developed by William Erb in 1874 but first conceptualized by Plato. This theory was purposed that we do not have specific organs in the body for pain, rather the sensation of pain was dependent on the intensity of the stimulus. For example, pain would occur if the stimulus caused strong activation of nerves and pain would not occur if it was a weaker stimulus. The shortcomings of this theory were it could not explain how people could experience an extremely noxious stimulus yet report no pain. For example, Henry Beecher 1956 reported soldier’s on the battlefield could entirely deny pain from an extensive wound. Nonetheless, this theory helps to further move pain science forward.
Intensity Theory Short Comings On What Is Pain
Does the pain experience rely on a pattern vs intensity or a specific pathway?
The Pattern theory developed by John Paul Nafe was suggested in 1929. This idea is the opposite of the specificity theory as Nafe argued there is no separate system for perceiving pain, touch, temperature. Instead, “sensory organs have an extensive range of responsiveness and respond to stimuli with differing relationships of intensity” (Jun Chen 2011). The sensory organ, once responsive to a stimulus would then code a signal or encoded pattern to the brain for further interpretation. The shortcoming of this theory is that other research supporting the specificity theory showed there are receptors or sense organs that are specific to each type of sensation.
Can these theories just all get along?
The next theory is argued to be the most influential and would revolutionize pain research. Instead of arguing the above theories, Ronald Melzack and Patrick Wall propose the Gate Control Theory of pain in 1965. They delicately put together the findings from the above theories and bridged the gap to develop this game-changing theory. Briefly, Melzack and Wall 1965 state, “no single theory so far proposed is capable of integrating the diverse theoretical mechanisms and have not received any substantial experimental verification.” Their theory proposed a stimulus enters the spinal cord through 3 differing areas and a “gate” is present that either sends the signal up to higher centers or inhibits the signal. For a further description of this theory click here. One of the revolutionary concepts in this theory was the additive of central control and acknowledgment that pain is multidimensional and complex. Mezlack and Wall changed the game but the theory also had its shortcomings. The theory failed to cover the true complexity of the brain and central command in the pain response. As stated earlier, a description of phantom limb pain or chronic pain persisting after healing occurred had not yet been described. In other words, the theory was incomplete.
Gate Control Theory Of Pain Shortcomings
Can we see a complete theory? Please!
Almost 30 years after introducing the Gate Control theory of pain, Melzack states, “yet, as historians of science have pointed out, good theories are instrumental in producing facts that eventually require a new theory to incorporate them.” He recognized the theory was not complete and further built off of the gate control theory to then propose the neuromatrix model!
Neuromatrix model of pain
Ronald Melzack 2001 stated, “the gate control theory’s most important contribution to understanding pain was its emphasis on neural mechanisms…The great challenge ahead of us to understand brain function.” In summary, this theory shows that pain is an output from the brain reliant on the inputs it receives. A detailed description is shown in the picture below and in the article here.
Mezlack’s work now allowed scientists to look at pain through physical, emotional, and cognitive factors. It taught us that tissue damage is not necessary for pain, a topic we will get further into later, and highlighted the true complexity of pain. However, it failed to account for the social constructs of pain.
How do we include all of the complexity into one theory?
We introduce you to the biopsychosocial model of pain. It is the most comprehensive explanation and describes pain as a result of complex interactions between biological, psychological, and sociological factors. Pain is an output 100 percent of the time from the brain and is dependent on the perception of the input from the above factors. The biopsychosocial model also helps to explain variance in performance.
It is important for us to know these older theories to understand where we are now. We highly encourage you to dive into the sources linked throughout for a more in-depth overview as desired. However, our history lesson is over and now we can answer, what is pain?
Look for this answer in Part 2 of this series!
In the meantime, aside from education, the first steps to combat pain is decreasing internal load and taking control of your movements. You can learn more about internal load here!
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About The Author
[P]REHAB Audio Experience Host
[P]REHAB Writer & Content Creator
Dillon is a Sports Physical Therapist, performance coach, and adjunct professor residing in Syracuse, NY whose passion is providing holistic solutions to improve all aspects of human performance. Along with working with clinical athletes across the lifespan, he provides on field coverage for youth and semi-professional teams. After his undergraduate studies at Syracuse University, he earned his Doctorate in Physical Therapy from SUNY Upstate Medical University. He practices wellness, prevention, and solution-based health care out of Goldwyn & Boyland, PT, and Core Fitness. In his free time, he enjoys family dinners, playing with his dog, and competing as a fitness athlete. Dillon honors the opportunity to join the [P]Rehab guys to influence and educate in a people first system!