Pain Pain Pain, the P-Word that’s been running us all through its fingers for who knows how long!
We in the sciences (especially clinical sciences) take pride in our experience of dealing with pain day in, and day out. We claim to have an understanding of what pain is and all it stands for.
After all, what is pain besides that nagging discomfort which comes after stubbing your toe or something right?
Still, we find ourselves face-to-face with biases, misinformation and unpreparedness whenever we encounter a situation that doesn’t fit that clear flow or ‘clinical picture’; which unsurprisingly happens more often than we care to admit. Resulting in misdiagnosis, ignored red flags, overdiagnosis, improper advice, and overall injustice.
A simple reason that I can think off the top of my head, is that we don’t really appreciate the immensity of the information available on pain through the ages.
Failing to put the ‘development’ of modern understanding of pain into perspective makes us overlook the bigger picture and can sometimes make us prone to fall for mechanistic fads and gimmicks.
For example, As a kid, while learning the metric system I often found myself wondering how different various multiples of distance could really be. A centimetre, a foot, or a meter didn’t seem much different to me. What actually helped me to understand the gradient of size was travelling 1000s of kilometres and those biology lessons where we did a microscopic analysis of cells, tissues and organisms.
Understanding the scale at both extremes made me appreciate the concept of scale and sciences (astrophysics, particle physics, microbiology, anatomy, etc.) like never before.
Thus,In this blog, I will try to put the history of pain, its understanding, influence and scope into perspective (if not in a simplified trajectory).
For the sake of said simplification, we’d divide history into 3 parts.
Ancient/Philosophical
Intermediate/Structural
Contemporary/Functional/(~BPS)
Let’s dive in with the flow.
1. Ancient Understanding of Pain:
Almost all the understanding of pain and related concepts in ancient times revolved around the philosophical and empirical nature of all which is observable about pain.
With spirituality at heart and limited understanding of the human body, most of the ancient theorists believed pain to be partly emotional, influenced by the flow of various humour, spirits and substances through the body to and from the brain or the heart. Resulting in the perception of pain.
The era-defining work in the ancient understanding of pain comes from ‘Treatise of Man’ a manuscript by René Descartes. Descartes in his influential (yet not entirely novel) work purported ‘mind-body dualism’ wherein he argued that the materialistic body and soul(mind) are two distinct entities and while the injury is a matter of the body, pain is felt in the mind (~ brain).
Certain misconceptions about how mechanistically Descartes viewed and described pain stem from the interpretation and translation of his work by Louise La Forge.
A closer read into the actual and following works of Descartes it’s seen that he attempted to make sense of how soul and body connected (like the perception of phantom limb pain, where the material body isn’t present but the pain is).
Another misconception arises from the most famous image in Pain and Neuroscience, The Illustration of the man beside fire by Louise La forge.
From the illustration, it seems that Descartes describes a specific pathway for pain, whereas Descartes played with the idea that ‘the pattern and rate of firing (intensity of tugging) of fibre provided adequate information to the brain about the stimulus intensity and quality’ an impressive assumption for the time.
(remember this while reading about specificity and intensity theories later)
Notable is the fact that almost all the theories and models of pain today have made assumptions based on and attempted to answer the misconceptions and questions posed in ancient times.
Practical highlights of ancient understanding of pain:
Pain is a sensation or perception?
Pain is an independent feeling.
There are pathways to carry pain.
2. Intermediate(modern) Understanding of pain:
The 19th to Mid 20th century period marks the most curious time in the understanding of pain as a whole, Where advancements in technology and understanding of the human body enabled various pioneers to attempt and answer questions about pain based on the ancient understanding of pain and modern understanding of anatomy.
On a side note (but really a complimentary track) To roughly understand how modern understanding of pain approaches the answers, we should appreciate how they went about collecting data to inform their theories. Skin being the largest, easily accessible, easily observable( both in injury, response and healing) organ in the human body; remained(/s) the target of pain-related experimentation throughout the modern era.
It can easily be pricked, poked, stabbed, sprayed with stuff and all sorts of stimulation with a reasonable outcome and easy to adjust experiments.
Thus, most of these theories are formulated around the sensation (receptors, fibres, relays, centres, etc.) of cutaneous pain. Hence, accounting for almost nothing besides acute nociception or laboratory-induced persistent stimulation leading to pain (almost nothing on muscular, visceral and persistent/chronic pain)
Now, Back to the modern understanding of pain.
Charles Bell in his landmark essay, Idea of a New Anatomy of the Brain (the early-1800s) proposed the idea that the brain isn’t a ‘common sensorium’ as previously ‘postulated’ (and influenced by) in the works of Descartes. He asserted that the brain is a heterogeneous structure with nerves and their fibres having specialised functions (bundled together just for the ease of distribution and organization). This led to a slew of research into what later turned out to be known as the ‘Specificity Theory’ of pain.
François Magendie’s work (the mid-1800s) and findings regarding the distinction between sensory and motor columns and pathways (later termed Bell-Megendie law) led to the pivotal shift towards acceptance of Specificity and understanding of the organization of the nervous system.
Johannes Müller, Erasmus Darwin, Pacini, Meissner, Merkel and Ruffini’s work in the coming decades cemented and provided further evidence that specific sensory qualia were encoded by dedicated nerve fibres.
William Richard Gowers and Charles-Édouard Brown-Séquard’s observations further explained the organization of the nervous system (the understanding of decussation of tracts and dissociated anaesthesia) explained how specificity could be the answer to all things ‘pain’.
Blix, Goldscheider and Von Frey’s findings of sensory spots on the skin finally made ‘pain’ a recognizable sensation (which previously was limited to ‘just perception’ by Aristotelian dogmatists)
Overlapping in time is the development of the ‘Intensity Theory’ of pain, where scientists influenced by the works of Plato, Erasmus Darwin & Wilhelm Erb proposed that there must be some form of summation(net intensity) that occurs for the subthreshold stimuli to become
unbearably painful (ignoring the specificity of receptors and sensations)
The era-defining work in the modern understanding of pain comes from the discoveries of Charles Scott Sherrington (1947) where he addressed some of the assumptions of the Specificity Theory in his proposed framework of nociception through Temporal and Spatial summations (Specificity and Radiation) that bridged the divide between specificity and Intensity theories.
The key shortcoming of Modern Understanding of pain resides in how and what these methods consider, and the simple answer is that most modern understanding considers structure in a mechanistic way to make sense of pain, which we now understand is much more complex than that.
Thus for instance, although the Specificity Theory appropriately described sensory receptors that are specific to nociceptive stimuli and primary afferents that show responses only to suprathreshold stimuli, it did not account for neurons in the central nervous system (CNS) that respond to both non-nociceptive and nociceptive stimuli (remember the WDR neurons?)
Also, as I mentioned earlier, studying cutaneous pain does not address issues pertaining to Deep tissue, Visceral, or Muscular pains.
With that in mind, Let’s discuss the contemporary understanding of pain;
Before we discuss Neuromatrix and beyond, We need to understand the magnitude of impact that Ronald Melzack and Charles Patrick (Pat) Wall’s landmark paper on the ‘Gate Control Theory of Pain’ had in the world of pain science and neuroscience.
‘Gate control theory’ attempted to address the shortcomings of all the previous theories (or their influence) based on aspects of each of these theories, supported by physiological data i.e.:
Melzack and Wall accepted that there are nociceptors and touch receptors. (specificity)
Fibres from these receptors synapse in two different regions within the dorsal horn of the spinal cord (Bell & Megendie’s work)
They proposed that the gate in the spinal cord is the substantia gelatinosa in the dorsal horn, which modulates the transmission of sensory information from the primary afferent neurons to transmission cells in the spinal cord. (Descarte’s work)
They explained that, when nociceptive information reaches a threshold that exceeds the inhibition elicited, it “opens the gate” and activates pathways that lead to the experience of pain and its related behaviours. (Specificity and Pattern theories)
Thus, reconciling the differences among(almost) all the previous theories and beliefs, and paving the way to what we currently understand pain to be.
Contemporarily, The understanding of pain has evolved past the structure, receptors and reception of pain to include context, beliefs, memory, previous experiences, stress, central and peripheral sensitization, downward modulation, cortical plasticity, neuroimmuno-humoral mechanisms and more.
(Unsurprisingly) A better compilation of all these aspects comes from the work of Ronald Melzack (2005): The neuromatrix theory of pain!
To simplify, the key observations of the neuromatrix theory are:
pain is a multidimensional experience produced by characteristic “neurosignature” patterns of nerve impulses generated by a widely distributed neural network – the “body-self neuromatrix” – in the brain
Output patterns of the body-self neuromatrix activate perceptual, homeostatic, and behavioural programs after injury, pathology, or chronic stress
Pain is produced by the output of a widely distributed neural network in the brain rather than directly by sensory input evoked by injury, inflammation, or other pathology.
Output is determined by multiple influences, of which the somatic sensory input is only a part, that converges on the neuromatrix.
Considering the somatic, affective and cognitive complexities that affect pain, its perception, and behaviour, neuromatrix theory (although being a CNS forward theory) provides enough intricacies to be considered while dealing with people in pain.
With the history of pain somewhat revised, remember the kind of treatments we developed to deal with pain based on the understanding we had at the time,
From, Punishment and boycotts in the ancient times (Aristoteles and dark age influence)
Electrotherapeutics in the modern time (Pain gate, pattern and intensity theories)
Manual techniques in the recent times (specificity, and mechanistic views)
To, Psychobehavioral interventions for persistent pain: like CBT (neuromatrix, MOM)
Interventions/treatments have become less specific and more accommodating to the entire context of the painful experiences, as we now understand that even acute nociceptive pain is multidimensional!
Thus, it is in our interest to grow with time, it’s only ethical that we learn from the past, and understand the vastness of that which is known and especially that which isn’t.
Hopefully, this blog provides you with some perspective on how far we’ve come in our understanding of pain and how important it is to move forward, let go of the ‘comforting sureties’ and change for good!.
For more go to Physio Explored Blogs
Cover Photo by Mikhail Nilov from Pexels
Disclaimer: This blog is for educational purposes only.
*more on MOM in upcoming blogs.
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