DECONSTRUCTING PAIN PERCEPTION THEORIES - CAN PHYSICAL PAIN BE BLOCKED OUT? (PART 1)

Despite being one of the most common reasons people seek out medical attention, relatively little is known about the origins of pain and why it is crucial in shaping the quality of life.

Scientists have been striving to understand pain for thousands of years in an attempt to provide better relief to those in need. The following article aims to describe what pain is and how it can be effectively blocked out in the most beneficial way possible. Theories of pain are discussed below in line with the latest research on the subject, highlighting how pain has multiple dimensions and its management often requires a multi-pronged approach.

Pain is Still Incompletely Understood

It took scientists quite a long time to define pain in a way that broadly covers all its applications. Even after thousands of years of exploring the subject, there is still a lack of a complete understanding of what pain is today.

Pain is often viewed as a signal pertaining to harm. On a physical level, pain usually indicates injury and forms a necessary part of the healing process. Pain experienced on a mental-emotional level often signifies the need for healing as well, in the form of negative emotion, psychological appraisal (consideration), and consolidation (change).

This general definition still does not encompass every person’s unique perception of pain, which moderates the way in which pain is felt at the individual level.

How pain is measured. As pain is subjective and not completely definable, it is typically difficult to measure. Researchers have managed to measure pain in terms of the following features:

• Pain threshold is the lowest intensity at which a stimulus is perceived as painful or the upper limit of pain tolerance. It is relatively similar between individuals with respect to physical stimuli such as heat. Due to the relative similarity, this can be assessed (almost) objectively.
• Pain intensity is described as the magnitude of experienced pain and differs between individuals.^[1] This can be assessed subjectively.
• Pain interference is another measurement used to assess pain, which refers to the extent to which the pain interferes with the quality of life, overall well-being, sleep, life satisfaction, and engagement with physical, emotional, social, cognitive, and creative activities.^[2]

Historical Theories of Pain

Theories of pain have historically made slow progress. While the study of pain is necessary for the alleviation of suffering and to better understand the healing process, investigation of pain is difficult for ethical reasons and due to the fact that pain is partly a subjective experience.

The following briefly explores historical theories of pain, leading up to the current perspective on what pain is today.

• Pain as a Non-Physical Emotional Entity. The oldest records that describe theories of pain revealed that, historically, concepts of pain were rooted in both medical observations and religious or spiritual beliefs. The first medical observations of pain acknowledged that pain was itself a unique ‘emotion’ felt in response to psychological or physical injury or harm. Up until the 19^th century, physical and psychological pain were believed to be separate and unable to influence one another (referring to the cartesian dualistic theory of pain). These theories of pain were the first to highlight that pain is less of a physical entity and that subjective psychological influences, such as guilt and other emotions, are able to control pain perception and intensity. They still did not completely explain interindividual differences in pain, as every person will still perceive pain differently for the same injury.
• Pain as a Complex Physical Sensation. In the mid-1800s, the specificity theory of pain was proposed, stating that pain is the result of specific physical sensations that were received by a near-infinite number of receptors on the surface of the skin, which relayed this sensory information to the brain. These receptors were later classified into four main sensory modalities: touch, pain (injury), heat, and cold. This builds on the previous understanding that physical pain is separate from psychological pain, yet it begins to do away with the notion that the two are unrelated. This was partially expanded upon by the pattern theory of pain, which explains that the sensory input from skin receptors generates a unique pattern that gets decoded by the brain, dictating the degree and type of pain experienced. Nevertheless, both theories still failed to answer the fact that some forms of pain manage to persist long after a wound has healed, and other forms of pain arise for no apparent reason on a chronic basis.
• The Gate Control Theory. The gate control theory of pain was proposed in 1965 and explained how signals from the periphery reach the brain through the spinal cord. Science revealed that signals from receptors in the periphery need to make it to the substantia gelatinosa in the dorsal horn before traveling up the spine to reach the brain stem, the somatosensory cortex and other relevant brain areas for the brain to process sensations of pain. After consolidation, signals from the brain get transmitted back through to the periphery via transmission cells, also found in the dorsal horn. It is called the gate control theory, as the signals may be dampened (or amplified) at the dorsal horn or in the fibers of the spinal cord, which serve as a gate control mechanism. If the signals are too weak, pain is not experienced. This was the first reference to what is now referred to as the ascending and descending pathways of pain. The gate control theory of pain is still used throughout research today to explore the neurotransmission mechanisms underpinning pain. Despite contributing massively towards the current understanding of pain, it fails to fully explain chronic pain disorders or those who experience pain in ‘phantom limbs’ post-amputation.
• The Neuromatrix Model of Pain. Following on from the gate control theory, the neuromatrix model was proposed in the mid-90’s in order to explain recurrent sensations of pain in the absence of a physical stimulus. This model sees pain as an entirely brain-derived sensation, where the pain is a product of signals within the neuromatrix of pain, which consists of connections between several different brain regions. These include the spinal cord, brainstem, and thalamus, the somatosensory and motor cortices, the limbic system, the insular cortex, and the prefrontal cortex. Besides processing physical sensations from the periphery, many of these brain areas are involved in emotional processing, reasoning, memory formation, self-awareness, and identity formation. Signals between these brain areas can diminish or amplify pain as well as form memories associated with pain and its perception that either perpetuate it or allow for its avoidance in the future. It also highlights how the stress response is intimately linked to pain and its perception. This begins to tie in with the early notion that pain is partly a subjective experience with an emotional component.

Biopsychosocial Theory of Pain: The Current Theory

The biopsychosocial theory of pain is the latest model used for understanding pain. It proposes that the mind cannot be separated from the body with respect to pain and disease, which necessitates that biological, psychological, and sociological factors are taken into consideration when approaching the topic. These factors impact overall mental and physical well-being.

Main Components of Pain. The concept of pain is further divided into four main components:

• Nociception is the sensory signal sent to the brain from the periphery that allows for a painful sensation to be registered.
• Pain is the subjective experience that occurs as a result of the brain’s processing of a potentially painful stimulus from the periphery.
• Suffering is the emotional response to pain (the subjective experience of pain detection).
• Pain Behaviors describe the physical response or action a person takes in response to pain.

Nociception and pain are conscious experiences, whereas suffering and pain-related behaviors can be either conscious or subconscious.

Pain is More than Nociception. These four components are very important when aiming to tackle pain therapeutically. The latest medical approaches towards treating pain aim to block nociception, putting an end to the sensory signal of pain before it can be processed and outwardly felt. This approach does not address the remaining 75% of a person’s experience of pain, which pertains to their perception, emotional reaction, mental understanding, and their ability to respond.^[3]

Expansions on the Biopsychosocial Theory of Pain: Supporting Evidence

See part 2 for expansions on the biopsychosocial theory of pain as well as suggestions on how to block out physical pain.

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