Neurophysiological Mechanisms of Pain Perception and Management
Benjamin Tangkamolsuk, Quang La, Darren Phan
Medical Community and Research
Tuesday 27th February 2024
Abstract
This article goes over the functionalities of neurophysiological mechanisms of pain perception and management. It covers things such as how our body understands and communicates pain through neural pathways, to pain management strategies and medications used in hospitals and lastly concluding with the assessment of pain.
Keywords: Neurophysiology, Medicine, Health, Pain, Physiology
Article
Pain is a discomfort or suffering, gained from injury or illness. The painful feelings are a global issue that affects every single one of us (except those with certain conditions) and it truly is a hated feeling to have. Although most, if not all, humans on Earth have experienced pain, not a lot of people actually know and understand how we perceive pain. Despite people suffering from this dreadful feeling everyday, not a lot of people shed light onto possible pain management strategies either. Although there is an abundance of resources pertaining pain management and understanding of pain available online, most of them are inclined towards clinical practice, rather than basic understanding of the concept. This article goes over the perception of pain, as well as the management of pain in humans. We aim to create research that puts it into a more simplified and easy to understand explanation of the topic as well as promote current efforts to improve pain management in clinical settings.
Complex neuronal pathways that extend from the peripheral nervous system to different parts of the brain are involved in the sense of pain. Comprehending these pathways is essential to clarifying the neurophysiological processes that underlie the perception and regulation of pain.
A painful stimulus originates in the periphery, where noxious stimuli like pressure, heat, or tissue damage are detected by specialized sensory neurons known as nociceptors. Most of these nociceptors are unmyelinated or sparsely myelinated fibers that use the spinal cord to send signals to the central nervous system (CNS).
Nociceptive signals are triggered by noxious stimuli and proceed via the spinal cord to the dorsal horn, where they fuse with second-order neurons. Neurotransmitters including glutamate and substance P are involved in this synapse. It is noteworthy that interneurons in the spinal cord emit inhibitory neurotransmitters such glycine and gamma-aminobutyric acid (GABA) to modulate pain signals.
The dorsal column-medial lemniscal route and the spinothalamic tract are the two primary pathways via which pain signals rise from the spinal cord. The dorsal column-medial lemniscal route sends information about the modality and exact position of the stimulus, whereas the spinothalamic tract provides information about the location and severity of the pain. Numerous brain areas involved in processing and interpreting pain receive nociceptive signals through these pathways.
Pain signals are sent to higher brain areas for further processing through the thalamus, which acts as an essential relay station. The somatosensory cortex receives nociceptive information from the thalamus and integrates it with other sensory inputs to generate the conscious sensation of pain. The thalamus is also involved in controlling attention to pain stimuli and gating nociceptive signals.
The sensation of pain is not only sensory; affective and emotional aspects are also involved. The limbic system, which includes the anterior cingulate cortex and amygdala, is essential for processing the affective components of pain. These areas have a role in modifying pain-related actions, controlling emotional responses to pain, and connecting pain with prior experiences.
Apart from the ascending pathways, the processing of pain is also significantly influenced by descending modulatory pathways that originate from higher brain areas. Along with other neurotransmitters like serotonin and norepinephrine, these pathways entail the release of endogenous opioids like endorphins and enkephalins. Descending pathways have a role in analgesia and pain regulation by either facilitating or inhibiting nociceptive signaling at the spinal cord level.
By harnessing brain imaging machinery, scientists have procured vital information about the brain regions involved with pain perception; these structures include the primary and secondary somatosensory cortex, anterior cingulate cortex, prefrontal cortex, insular cortex, amygdala, thalamus, cerebellum, and the periaqueductal gray (PAG). Parts of the mesolimbic reward circuit, NAc & ventral tegmental area, are involved with processing chronic pain. On the other hand, the partnership of the prefrontal region & limbic system (NAc, VTA, amygdala, ACC) integrates/regulates emotional and motivational response. Each influences the other, as you may know emotion/motivation governs pain perception. Assimilating the contrasting functions of the brain can offer hypothetical solutions to pain disorders. As an example, studies regarding patients with back pain had greater influence from NAc’s & mPFC. Scientists suggest certain regions in emotion exert a varying amount of chronification on pain, like the amygdala and mPFC. Additionally, fluctuations in emotion, motivation, or reward-related circuits may affect disorders with emotion in chronic pain. This evidence is also proven by a study of reduction of gray matter in the two regions, amygdala and hippocampus. It all correlates with chronic pain and emotional changes. Much of the influence of chronic pain revolves around emotions; studies have proven that chronic pain is often correlated with depression (i.e. neuroplasticity, neurobiological mechanisms, monoamine transmitters: serotonin, dopamine, and norepinephrine decreased in both depression and chronic pain patients.).
In the modern day, there are a multitude of ways to manage pain in a clinical setting, from commonly known methods such as medications, down to things such as physical therapy. Let’s start with talking about medications. Pain management medications in the modern day are usually in the form of opioids, a medication in which it interacts with the brain cells, reducing the amount of pain the body can send to the brain. They latch onto the receptors in our spine and brain in order to block the signals from reaching the brain, hence reducing the amount of pain we feel. But by doing this, it causes a “euphoria” sensation within the body, making the person feel what is commonly known as “high”. Opioids can cause severe addiction and withdrawal and can have severe consequences, sometimes leading to death. Previously in the US, the use of opioids in pain management has resulted in severe, unaddressed addiction to the opioids resulting in the misuse of the medications and consequently resulting in death due to overdose. It has been so severe to the point it has caused an entire crisis within the United States.
Another well known alternative that is used, not only for pain relief but also for rehabilitation of movement after injuries would be physical therapy. PT or Physical Therapy is essentially performing specific exercises in order to alleviate the pain, rather than the pain. Although it seems simple, physical therapists need to go through intensive training and learning in order to be certified. It is to be noted that physical therapy is usually a method of pain management issued to people with long term pain (chronic pain). It is also recommended to consult your primary care physician before seeking a physical therapist.
In addition to physical therapy, another common method of alleviating pain would be massage. An example of this would be the adored Thai Massage, where they aim to relax the muscles in the body through a number of techniques.
Going back to clinical practices, another upcoming treatment that is becoming more and more available is using TENS. TENS, or Transcutaneous electrical nerve stimulation, as the name suggests, gives off low-voltage electric currents directly to the skin over the area you have pain. By doing this, it reduces the amount of pain signals, hence relaxing the muscles and reducing pain. Although this has shown to work in clinical trials, TENS does not have high-quality scientific evidence backing it up.
And lastly, a commonly used short-term alternative that you could also choose is using an ice pack. A quick and easy way to alleviate pain by reducing the amount of inflammation in an injury. By reducing the amount of inflammation in an injury, it reduces the amount of discomfort the body experiences and hence reduces the amount of pain. Reducing inflammation has also shown to improve healing rates on injuries.
Although the general processes involved in pain perception and modulation can be understood through an understanding of the neurophysiological mechanisms underlying these processes, it is important to acknowledge the substantial individual heterogeneity in pain perception and response. Numerous factors, including biological, psychological, and societal causes, might have an impact on this variability.
Individual variations in pain sensitivity and tolerance are influenced by biological variables. Genetic variations can affect an individual’s vulnerability to pain disorders or reaction to analgesic drugs. Examples of these genes include those encoding for neurotransmitter receptors or enzymes involved in pain processing. Individual variations in pain perception can also be attributed to variations in neuroanatomical structures, such as the density of nociceptive fibers or the effectiveness of descending pain modulation pathways.
An individual’s perception of pain is greatly influenced by psychological variables. The experience and management of pain can be influenced by cognitive processes like expectancy, coping strategies, and attention. For instance, people who experience high levels of anxiety, despair, or catastrophizing may find pain to be more severe and incapacitating. Furthermore, pain sensitivity and the emergence of chronic pain syndromes can be influenced by past experiences, trauma, and conditioning.
The sociocultural elements of upbringing, education, financial standing, and cultural norms all have a role in the individual differences in how pain is perceived and managed. People’s expression, interpretation, and coping mechanisms with pain can be influenced by cultural views and attitudes toward pain, as well as by their access to social support networks and medical services. Furthermore, a person’s desire to ask for assistance or stick to pain management techniques may be impacted by the stigma associated with pain and its treatment.
It’s critical to understand that these variables frequently interact and have an impact on one another, resulting in intricate patterns of individual variability in pain perception and modulation. For instance, biological predispositions may enhance susceptibility to chronic pain disorders when they mix with psychological factors like stress or trauma. Similar to this, societal influences can mold a person’s attitudes and ideas about pain, which in turn can affect how they experience pain and react to it.
Developing individualized approaches to pain management requires an understanding of the heterogeneity across individuals in pain perception and modulation. therapy outcomes and patient satisfaction can be increased by customizing therapy procedures to address the distinct biological, psychological, and sociocultural aspects influencing each person’s experience of pain. Furthermore, implementing a biopsychosocial model of pain management that takes into account how these variables interact can assist medical professionals in providing more thorough and successful pain management treatments.
In order for paramedics to assess a patient’s condition, procedures like OPQRST and The Stanford Five are employed for optimal evaluation of pain; these operations can dictate the care and aid a patient needs. OPQRST is an acronym for Onset, Provokes or Palliates, Quality, Radiates, Severity, and Time. A collected manner will not only improve cooperation but ease the patient by lowering anxiety levels. Onset is used to gather more information about the patient’s incident, e.g. “What were you doing when the pain started?” or, “Is your pain quick or a gradual build?”. Provokes or Palliates shouldn’t be overcomplicated; instead of asking, “What provokes your painful dilemma?”, ask “What actions increase or decrease the pain?”. It’s quite difficult to comprehend our surroundings and inquiries when pain is uncomfortable. Quality offers the patient a broader list of terms to describe their pain… asking limited questions such as, “Is your pain frequent or slow?” will confine them to two answers, yet none of them will correlate with their situation. Asking how they would describe their pain would result in more favorable assistance. Radiate gathers information about the location of pain. Once again, make sure to ask intelligible, real questions; “Where does your pain come from?” is better than “Does your pain radiate?”. Severity apprises the scale of pain. Understand that pain perception is relative or subjective, so don’t disregard “unrealistic” agony from a patient. Finally, time explains the duration before and after pain ensued. Understand that many healthcare professionals may use other acronyms that are interchangeable with OPQRST, such as SOCRATES, OLD CARTS, and SCHOLAR (the list proceeds). Rather than eliciting descriptions of the pain itself (OPQRST), The Stanford Five assesses pain perception that supports the patient’s predominant beliefs. It is composed of 5 steps: Cause, Meaning, Impact, Goals, and Treatment. Cause starts with asking the patient their reason of pain: “What do you think caused this pain?”. Why? Perhaps a patient feels more anxious if their primary beliefs are drawn false; some may feel more worrisome if they don’t know the cause of their discomfort, and ultimately perceive greater pain. Meaning: This refers to more psychological reasoning; an individual’s superstitions and beliefs that may require a diagnosis. Impact questions the effect of the pain upon their daily life; physical activity, socializing, etc. Goals ask the patient how their treatment should be prescribed and to what extent. Lastly, treatment is the patient’s opinion for the solution/resolvement of their diagnosis. These approaches have been employed by health-care professionals in order to protect the patient from excessive discomfort. At times like these, cooperation and patience are pivotal assets of controlling pain perception. For ages, scientists and medical professionals have been fascinated by the intricate phenomenon of pain perception. Although pain was originally believed to be a simple sensory experience, research has shown that it is complex, requiring both psychological and complicated neurological mechanisms. In this piece, we examine the Gate Control Theory, one of the most well-known theories of pain perception, as well as a few supplementary hypotheses that shed light on the subtleties of pain processing.
The Gate Control Theory, which was put forth by Ronald Melzack and Patrick Wall in 1965, transformed our knowledge of how pain is perceived by proposing the idea that the spinal cord contains a “gate” mechanism. This theory suggests that pain signals are regulated by neural circuits in the spinal cord rather than passively traveling from the periphery to the brain. The gate functions as a regulating mechanism that can increase or prevent pain impulses from reaching the brain. The gate’s ability to open or close can be influenced by a number of factors, including physical stimulation and emotional state, which can control how painful something feels. A framework for comprehending phenomena like the placebo effect, in which the brain’s natural processes can alter perceptions of pain, is provided by the Gate Control Theory.
The Endogenous Opioid System, which contends that the body creates endorphins and enkephalins on its own, is another significant idea in pain regulation. By attaching to certain receptors in the brain and spinal cord, these endogenous opioids block the transmission of pain signals and provide analgesic benefits. Since this mechanism was discovered, non-pharmacological therapies like acupuncture and exercise that encourage the release of endogenous opioids have also been developed in order to treat pain.
The Neuromatrix Theory of Pain, which was developed by neuroscientist Ronald Melzack, builds on the Gate Control Theory by arguing that nociceptive input alone does not determine pain perception; rather, a “body-self neuromatrix” that incorporates sensory, cognitive, and emotional factors also plays a role. This hypothesis states that pain is a subjective experience that is influenced by memories, attention, and pain-related beliefs. A comprehensive framework for comprehending chronic pain disorders and the individual differences in pain perception is offered by the Neuromatrix Theory.
The Biopsychosocial Model highlights the interplay between biological, psychological, and social elements in influencing pain perception and experience in addition to these neurobiological theories. According to this paradigm, pain is not just a sensory experience; it is also influenced by a variety of other variables, including stress, social support, cultural beliefs, and prior experiences. The Biopsychosocial Model emphasizes the significance of a thorough approach to pain management that takes into account both biological and psychological variables by taking into account the multifaceted nature of pain.
The Gate Control Theory provides important insights into the intricacies of pain perception, as does the Endogenous Opioid System, Neuromatrix Theory of Pain, and Biopsychosocial Model, among other complementary theories. By comprehending the interaction of neurological processes, psychological elements, and social environments, medical practitioners can create more potent pain management plans and enhance the lives of pain sufferers.
This article emphasizes the crucial role of understanding how we perceive and manage pain. Understanding how the nervous system interplays with neurotransmitters and also the brain regions involved in pain processing. This paper also brings light to the significance of pain management and the future for any other methods of eliminating pain. Lastly, it underscores the need for continued research to elucidate the intricate details of these mechanisms, ultimately paving the way for improved clinical approaches to pain perception and management.
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