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A unified theory of pain
Commentary
A Unified Theory-of Pain It May Not Be Possible Mark P. Jensen
taats, Hekmat, and Staats point out, correctly, that pain is an extremely complex phenomenon that involves many interrelated biological, psychological, and social components. They acknowledge that existing pain theories have gone far to advance our understanding of pain, but they criticize these theories for being too limited. For example, the central hypothesis of gate control theory is that nociceptive information is modulated at the level of the dorsal horn [11]. Although gate control theory continues to inspire a wealth of research and increased knowledge in the pathophysiology of pain [1,12], it has little to say about other specific pain components, such as personality or environmental factors. Similarly, the operant approach focuses on the effects of environmental stimuli on pain behavior [4]. Like gate control theory, this approach has led to a large body of research and the development of effective clinical interventions [6,10,22]. However, it does not address the underlying pathophysiology of pain or the effects of pain beliefs on adaptation. The cognitive-behavioral approach emphasizes how people cope with pain, their thoughts about pain, and how these impact subsequent pain and functioning [21]. Again, hypotheses generated from this approach have been tested in a large number of research studies, and clinical interventions based on cognitivebehavioral theory have benefited a large number of individuals [2,22]. However, cognitive-behavioral theory does not specify how beliefs and coping impact pain at the physiological level. Staats et al. see a need for a theory of pain that could provide a framework for unification of extant pain theories and observations, -and they argue that psychological behaviorism provides the foundation for such a theory. After reading the Focus article, I believe
S
From the University of Washington, Seattle, WA. Reprint requests: Mark P. Jensen, PhD, University of Washington School of Medicine, Department of Rehabilitation Medicine, Box 356490, Seattle, WA 98195-6490.
210
that they have advanced our theoretical understanding of pain. However, I was not convinced that psychological behaviorism provides the unification that Staats et al. desire. In fact, a truly unified theory of pain may not be possible. Staats et al. begin with a list of what they see as the basic components of pain. Basic scientists or sociologists might feel slighted that their disciplines were underrepresented in this list. The biological and social aspects of pain were given only one category each, while psychological aspects were represented by five categories: learning, pain behavior, cognitive, emotion, and personality components. Like all current pain models, psychological behaviorism acknowledges the importance of multiple pain components but focuses primarily on one set or category of (in this case, psychological) factors [3,9,13,19,20]. This is not necessarily a weakness of the model, but it does not support psychological behaviorism as a unifying theory. The real strength of the approach proposed by Staats et al. is in their focus on the interactions of pain components. This level of theoretical analysis is underrepresented in extant pain theories. Although research psychologists have done a great deal of work relating the cognitive and behavioral components of pain to one another, and basic scientists have significantly advanced our understanding of how physiological components of pain interact, relatively little work has studied the links between the psychological and physiological components of pain. One need only read recent issues of Pain or Pain Forum to see that researchers studying psychological issues rarely cite basic scientists, and vice versa. Staats et al. demonstrate that such a focus is worthwhile, given the useful new hypotheses that emerge from their analysis. For example, they hypothesize that, owing to its physiological connection to the limbic system, nociceptive input will impact emotion and emotion will impact pain experience. This hypothesis illustrates how the physiology and psychology of pain might be linked and has clear clinical implications.
Pain Forum 5(3): 210-212, 1996
COMMENTARY/Jensen
Another strength of the psychological behaviorism model of pain is its focus on person ality and the relationships between personality and other components of the pain phenomenon. Most, if not all, pain clinicians understand that patient personality can play a sign ificant role in treatment outcome. Repeatedly, experience shows that the same treatment can have dramatically different effects on different people. While these differences appear at times to be related to environmental issues (I recall hearing about a patient leaving our multidisciplinary pain program because she was instructed by her lawyer to do so, despite-or perhaps because of-some initial positive results), it is clear that many times there is something about a particular patient's personality that can interfere with or enhance treatment outcome. Unfortunately, many pain clinicians have relatively little theoretical or pract ical understanding of personality. Staats , Hekmat , and Staats ' (15-17) theo ry of personality may be part icularly useful , since it is based to a large extent on learning theory. As Fordyce has elegantly argued (4-6,8), and as Staats et al. outline in the Focus article , learning theory is extremely useful for understanding the link between pain behavior and the immediate social environment. Where I believe the approach of Staats et al. may be weakest is in the assertion that psychological behaviorism provides a foundation for a unified theory of pain. A unified theory of pain should consist of a finite and hierarchical set of theoretical principles that explain how the various components of pain work and interact with one another. However, the principles of psycholog ical behaviorism outlined by Staats et al. do not provide this level of explanation for all the components of pain. For example, although psychological behaviorism is not inconsistent with pain models that explain in greater detail the pathophysiology of pain, the principles of psychological behaviorism do not naturally lead to an understanding of how nociception is transmitted from the periphery to the central nervous system. Thus , psychological behaviorism does not encompass theories that focus on pathophysiology (such as gate control theory) but stands alongs ide of them . The pain theories and principles that have historically been most influential , and have led to the greatest advances in our understanding of pain, have limited themselves to a single primary tenet or hypothesis concerning a pain component, or the relationship between two pain components. Three of those theories were mentioned by Staats et al.: gate control theory, .operant theory, and cognitive-behavioral theory. These theories have been useful because of, not in spite of, their limited focus . It would be useful to continue to explore the implications of these "limited" theories and also to consider and develop similar theories that explain subsets
211
of the many components of pain. There are many areas in need of theory develoment , including the links between pain physiology, pain affect, and pain behavior. In addition, there is a need for further analysis of more global cultural issues as they relate to pain [7,18}. The avenue of theory development I propose is fundamentally different from that proposed by Staats et al. They call for a single theory that encompasses most , or all, of the components of pain." An alternative strategy for building an understanding of pain is to acknowledge that the different components of pain , and the relationships between them , may require a collection of unique, but complementary, theories. One way to picture this viewpo int is to envision pain as a house. Most houses consist of many specific materials (wood, brick , metal), systems (heating/cooling, electrical , plumbing) , and areas (for storage, sleeping , cooking , and eating). How these parts are des igned and how they work together are influenced by the house builder's culture , learn ing, motivations , and personality, among many other factors . If you want to understand how a particular house might work (and how to fix it if something goes wrong) , you must have an understanding of its mater ials, systems , and areas, and how these all work together. Theories of wood (wood burns at certain temperatures, wood can rot when it becomes moist , etc.) may be relatively unrelated to theories of heating systems, but both are necessary in order to understand houses . It is the collect ion of these theories that makes up our understand ing of complex systems such as houses, automobiles, persons, nations, and pain. To search for a single unified theory of houses , or of pain, may cont ribute to our knowledge by providing insights into factors not explo red by specific theories, but will probably, ultimately not be successful.
References 1. Abram SE: Advances in chronic pain management since gate control. Reg Anesth 18:66-81 , 1993 2. Fernandez E, Turk DC: The utility of cognitive coping strategies for altering pain perception: a meta-analysis. Pain 38: 123-135, 1989 3. Flor H, Birbaumer N, Turk DC: The psychobiology of chronic pain. Adv Behav Res Ther 12:47-84, 1990 4. Fordyce WE: Behavioral methods for chronic pain and illness. Mosby, S1. Louis, MO, 1976 5. Fordyce WE: Environmental factors in the genesis of low back pain. pp. 659-666. In Bonica JJ, Liebeskind JC, Albe-
' Interestingly, the central tenet of psychological behaviorism they propose as a unifying principle (that pain is a form of negative emotional response) is actually a focus on the link between two pain components (pain physiology and pain psychology ); an interesting hypothesis, but hardly a unifying principle.
212
6.
7.
8.
9. 10.
11. 12. 13.
14.
COMMENTARY/Jensen
Fessard DG (eds): Advances in pain research and therapy. Raven Press, New York, 1979 Fordyce WE: Learned pain: pain as behavior. pp. 291-299. In Bonica JJ (ed): The management of pain, 2nd ed. Lea & Febiger, Philadelphia, 1990 Fordyce WE (ed): Back pain in the workplace: management of disability for nonspecific conditions. IASP Press, Seattle, 1995 Fordyce WE, Roberts AH, Sternbach RA: The behavioral management of chronic pain: a response to critics. Pain 22:113-125, 1985 Karoly P, Jensen MP: Multimethod assessment of chronic pain. Pergamon Press, Oxford, 1987 Keefe FJ, Gil KN, Rose SC: Behavioral approaches in the multidisciplinary management of chronic pain. Clin Psychol Rev 6:87-113, 1986 Melzack R, Wall PO: Pain mechanisms: a new theory. Science 150:971-979,1965 Melzack R, Wall PO: The challenge of pain. Basic Books, New York, 1982 Novy OM, Nelson DV, Francis PJ, Turk DC: Perspectives of chronic pain: an evaluative comparison of restrictive and comprehensive models. Psychol Bull 118:238-247, 1995 Skinner BF: Science and human behavior. Macmillan, New York, 1953
15. Staats AW: Social behaviorism . Dorsey Press, Homewood , IL, 1975 16. Staats AW: Behaviorism with a personality: the paradigmatic behavior assessment approach. pp. 244-296. In Nelson RO, Hayes SC (eds): Conceptual foundations of behavioral assessment. Guilford Press, New York, 1986 17. Staats AW: Personality and abnormal behavior: a unified theory. Pergamon Press, New York (in press) 18. Sullivan MS: Pain in language : from sentience to sapience. Pain Forum 4:3-14, 1995 19. Syrjala KL, Chapko ME: Evidence for a biopsychosocial model of cancer treatment-related pain. Pain 61:69-79, 1995 20. Turk DC, Holzman AD: Chronic pain: interfaces among physical, psychological, and social parameters. pp. 1-9. In Holzman AD, Turk DC (eds): Pain management: a handbook of psychological treatment approaches . Pergamon Press, New York, 1986 21. Turk DC, Meichenbaum 0 , Genest M: Pain and behavioral medicine: a cognitive-behav ioral perspective. Guilford Press, New York, 1983 22. Turner JA, Chapman CR: Psychological interventions for chronic pain: a critical review. II. Operant conditioning, hypnosis, and cognitive-behavioral therapy. Pain 12: 23-46,1982
A Unified Theory-of Pain It May Not Be Possible Mark P. Jensen
taats, Hekmat, and Staats point out, correctly, that pain is an extremely complex phenomenon that involves many interrelated biological, psychological, and social components. They acknowledge that existing pain theories have gone far to advance our understanding of pain, but they criticize these theories for being too limited. For example, the central hypothesis of gate control theory is that nociceptive information is modulated at the level of the dorsal horn [11]. Although gate control theory continues to inspire a wealth of research and increased knowledge in the pathophysiology of pain [1,12], it has little to say about other specific pain components, such as personality or environmental factors. Similarly, the operant approach focuses on the effects of environmental stimuli on pain behavior [4]. Like gate control theory, this approach has led to a large body of research and the development of effective clinical interventions [6,10,22]. However, it does not address the underlying pathophysiology of pain or the effects of pain beliefs on adaptation. The cognitive-behavioral approach emphasizes how people cope with pain, their thoughts about pain, and how these impact subsequent pain and functioning [21]. Again, hypotheses generated from this approach have been tested in a large number of research studies, and clinical interventions based on cognitivebehavioral theory have benefited a large number of individuals [2,22]. However, cognitive-behavioral theory does not specify how beliefs and coping impact pain at the physiological level. Staats et al. see a need for a theory of pain that could provide a framework for unification of extant pain theories and observations, -and they argue that psychological behaviorism provides the foundation for such a theory. After reading the Focus article, I believe
S
From the University of Washington, Seattle, WA. Reprint requests: Mark P. Jensen, PhD, University of Washington School of Medicine, Department of Rehabilitation Medicine, Box 356490, Seattle, WA 98195-6490.
210
that they have advanced our theoretical understanding of pain. However, I was not convinced that psychological behaviorism provides the unification that Staats et al. desire. In fact, a truly unified theory of pain may not be possible. Staats et al. begin with a list of what they see as the basic components of pain. Basic scientists or sociologists might feel slighted that their disciplines were underrepresented in this list. The biological and social aspects of pain were given only one category each, while psychological aspects were represented by five categories: learning, pain behavior, cognitive, emotion, and personality components. Like all current pain models, psychological behaviorism acknowledges the importance of multiple pain components but focuses primarily on one set or category of (in this case, psychological) factors [3,9,13,19,20]. This is not necessarily a weakness of the model, but it does not support psychological behaviorism as a unifying theory. The real strength of the approach proposed by Staats et al. is in their focus on the interactions of pain components. This level of theoretical analysis is underrepresented in extant pain theories. Although research psychologists have done a great deal of work relating the cognitive and behavioral components of pain to one another, and basic scientists have significantly advanced our understanding of how physiological components of pain interact, relatively little work has studied the links between the psychological and physiological components of pain. One need only read recent issues of Pain or Pain Forum to see that researchers studying psychological issues rarely cite basic scientists, and vice versa. Staats et al. demonstrate that such a focus is worthwhile, given the useful new hypotheses that emerge from their analysis. For example, they hypothesize that, owing to its physiological connection to the limbic system, nociceptive input will impact emotion and emotion will impact pain experience. This hypothesis illustrates how the physiology and psychology of pain might be linked and has clear clinical implications.
Pain Forum 5(3): 210-212, 1996
COMMENTARY/Jensen
Another strength of the psychological behaviorism model of pain is its focus on person ality and the relationships between personality and other components of the pain phenomenon. Most, if not all, pain clinicians understand that patient personality can play a sign ificant role in treatment outcome. Repeatedly, experience shows that the same treatment can have dramatically different effects on different people. While these differences appear at times to be related to environmental issues (I recall hearing about a patient leaving our multidisciplinary pain program because she was instructed by her lawyer to do so, despite-or perhaps because of-some initial positive results), it is clear that many times there is something about a particular patient's personality that can interfere with or enhance treatment outcome. Unfortunately, many pain clinicians have relatively little theoretical or pract ical understanding of personality. Staats , Hekmat , and Staats ' (15-17) theo ry of personality may be part icularly useful , since it is based to a large extent on learning theory. As Fordyce has elegantly argued (4-6,8), and as Staats et al. outline in the Focus article , learning theory is extremely useful for understanding the link between pain behavior and the immediate social environment. Where I believe the approach of Staats et al. may be weakest is in the assertion that psychological behaviorism provides a foundation for a unified theory of pain. A unified theory of pain should consist of a finite and hierarchical set of theoretical principles that explain how the various components of pain work and interact with one another. However, the principles of psycholog ical behaviorism outlined by Staats et al. do not provide this level of explanation for all the components of pain. For example, although psychological behaviorism is not inconsistent with pain models that explain in greater detail the pathophysiology of pain, the principles of psychological behaviorism do not naturally lead to an understanding of how nociception is transmitted from the periphery to the central nervous system. Thus , psychological behaviorism does not encompass theories that focus on pathophysiology (such as gate control theory) but stands alongs ide of them . The pain theories and principles that have historically been most influential , and have led to the greatest advances in our understanding of pain, have limited themselves to a single primary tenet or hypothesis concerning a pain component, or the relationship between two pain components. Three of those theories were mentioned by Staats et al.: gate control theory, .operant theory, and cognitive-behavioral theory. These theories have been useful because of, not in spite of, their limited focus . It would be useful to continue to explore the implications of these "limited" theories and also to consider and develop similar theories that explain subsets
211
of the many components of pain. There are many areas in need of theory develoment , including the links between pain physiology, pain affect, and pain behavior. In addition, there is a need for further analysis of more global cultural issues as they relate to pain [7,18}. The avenue of theory development I propose is fundamentally different from that proposed by Staats et al. They call for a single theory that encompasses most , or all, of the components of pain." An alternative strategy for building an understanding of pain is to acknowledge that the different components of pain , and the relationships between them , may require a collection of unique, but complementary, theories. One way to picture this viewpo int is to envision pain as a house. Most houses consist of many specific materials (wood, brick , metal), systems (heating/cooling, electrical , plumbing) , and areas (for storage, sleeping , cooking , and eating). How these parts are des igned and how they work together are influenced by the house builder's culture , learn ing, motivations , and personality, among many other factors . If you want to understand how a particular house might work (and how to fix it if something goes wrong) , you must have an understanding of its mater ials, systems , and areas, and how these all work together. Theories of wood (wood burns at certain temperatures, wood can rot when it becomes moist , etc.) may be relatively unrelated to theories of heating systems, but both are necessary in order to understand houses . It is the collect ion of these theories that makes up our understand ing of complex systems such as houses, automobiles, persons, nations, and pain. To search for a single unified theory of houses , or of pain, may cont ribute to our knowledge by providing insights into factors not explo red by specific theories, but will probably, ultimately not be successful.
References 1. Abram SE: Advances in chronic pain management since gate control. Reg Anesth 18:66-81 , 1993 2. Fernandez E, Turk DC: The utility of cognitive coping strategies for altering pain perception: a meta-analysis. Pain 38: 123-135, 1989 3. Flor H, Birbaumer N, Turk DC: The psychobiology of chronic pain. Adv Behav Res Ther 12:47-84, 1990 4. Fordyce WE: Behavioral methods for chronic pain and illness. Mosby, S1. Louis, MO, 1976 5. Fordyce WE: Environmental factors in the genesis of low back pain. pp. 659-666. In Bonica JJ, Liebeskind JC, Albe-
' Interestingly, the central tenet of psychological behaviorism they propose as a unifying principle (that pain is a form of negative emotional response) is actually a focus on the link between two pain components (pain physiology and pain psychology ); an interesting hypothesis, but hardly a unifying principle.
212
6.
7.
8.
9. 10.
11. 12. 13.
14.
COMMENTARY/Jensen
Fessard DG (eds): Advances in pain research and therapy. Raven Press, New York, 1979 Fordyce WE: Learned pain: pain as behavior. pp. 291-299. In Bonica JJ (ed): The management of pain, 2nd ed. Lea & Febiger, Philadelphia, 1990 Fordyce WE (ed): Back pain in the workplace: management of disability for nonspecific conditions. IASP Press, Seattle, 1995 Fordyce WE, Roberts AH, Sternbach RA: The behavioral management of chronic pain: a response to critics. Pain 22:113-125, 1985 Karoly P, Jensen MP: Multimethod assessment of chronic pain. Pergamon Press, Oxford, 1987 Keefe FJ, Gil KN, Rose SC: Behavioral approaches in the multidisciplinary management of chronic pain. Clin Psychol Rev 6:87-113, 1986 Melzack R, Wall PO: Pain mechanisms: a new theory. Science 150:971-979,1965 Melzack R, Wall PO: The challenge of pain. Basic Books, New York, 1982 Novy OM, Nelson DV, Francis PJ, Turk DC: Perspectives of chronic pain: an evaluative comparison of restrictive and comprehensive models. Psychol Bull 118:238-247, 1995 Skinner BF: Science and human behavior. Macmillan, New York, 1953
15. Staats AW: Social behaviorism . Dorsey Press, Homewood , IL, 1975 16. Staats AW: Behaviorism with a personality: the paradigmatic behavior assessment approach. pp. 244-296. In Nelson RO, Hayes SC (eds): Conceptual foundations of behavioral assessment. Guilford Press, New York, 1986 17. Staats AW: Personality and abnormal behavior: a unified theory. Pergamon Press, New York (in press) 18. Sullivan MS: Pain in language : from sentience to sapience. Pain Forum 4:3-14, 1995 19. Syrjala KL, Chapko ME: Evidence for a biopsychosocial model of cancer treatment-related pain. Pain 61:69-79, 1995 20. Turk DC, Holzman AD: Chronic pain: interfaces among physical, psychological, and social parameters. pp. 1-9. In Holzman AD, Turk DC (eds): Pain management: a handbook of psychological treatment approaches . Pergamon Press, New York, 1986 21. Turk DC, Meichenbaum 0 , Genest M: Pain and behavioral medicine: a cognitive-behav ioral perspective. Guilford Press, New York, 1983 22. Turner JA, Chapman CR: Psychological interventions for chronic pain: a critical review. II. Operant conditioning, hypnosis, and cognitive-behavioral therapy. Pain 12: 23-46,1982