reflections by pain medicine experts. In a 2004 lecture, John D. Loeser recalls Encyclopedia Britannica’s definition of disease as “an impairment of the normal state of an organism that interrupts or modifies its vital functions” and concludes that since chronic pain certainly does modify functioning, in many different ways, it has to be recognized as a disease in its own right. The efforts in providing a specific biologic characterization of pain as a disease continues in the 21st century when crucial studies revealed the pathologic features associated with persistent pain, especially at the nervous system level. In his 2004 lecture at the Congress of the World Institute of Pain, Ronald Melzack described chronic pain syndromes to be caused as a result of “neural mechanisms gone awry.” In the last decade, significant progress in this field has been made, also thanks to the noteworthy contribution of neuroimaging studies. Compelling evidence of functional, structural, and chemical changes occurring in the brain in association with chronic pain was reported in a 2009 review by Tracey and Bushnell. These submissions support the idea Theories of pain in medical science Beyond merely adopting an acceptable definition for pain, different independent researchers and government-funded projects have developed theoretical frameworks describing the physiology of pain in humans and animal models. In this vein, different theoretical frameworks have been proposed to explain the physiological basis of pain, although none yet completely accounts for all aspects of pain perception. Here, this course provides a historical overview of the major
that chronic pain should be classified as a disease state—a condition characterized by a disordered nervous system (Arévalo-Martínez et al., 2022). That same year, the American Academy of Pain Medicine put forward a position paper recommending distinguishing between two categories of pain and proposing a new terminology for pain—eudyinia and maldynia, literally good pain and bad pain. Eudyinia is the pain described as: “a symptom of an underlying pathological disorder, either an illness or an injury.” On the other hand, Maldynia describes pathological pain. This refers to pain as a neuropathological disorder or disease process that occurs due to changes at the cellular and molecular levels (Mayoral Rojals et al., 2022). Today, it is generally regarded that persistent pain entails a pathologic reorganization of the neural system. This process can be due to several factors, such as a genetic predisposition, central sensitization mechanisms, and many other factors, which are at the core of the study of the etiology of pathologic pain conditions (Marchand et al., 2021). contributions, ideas, and competing theories of pain from ancient civilizations to Melzack and Wall’s gate control theory of pain. This course will explore the different pain theories postulated since the 17th century with a concluding overview of the current thinking on this subject. Arguably, the four most influential theories of pain perception include the specificity (or labeled line), intensity, pattern, and gate control theories of pain (Figure 1).
Figure 1: Schematic Representation of the Pain Theories
Note: From Ju Chen, 2011. Recreated under permission granted by the Creative Commons Attribution 4.0 International License of the Neuroscience Bulletin . Specificity theory of pain
Book Code: PYCA2725
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