Box 2: Explaining The Sensitization Model Much data has shown that individuals in chronic pain have better outcomes when they feel educated about their pain problem. Patients, especially those with centrally mediated myalgia or those with neuropathic pain, may benefit from an understanding of the sensitization model because it is factually accurate and provides some biological explanation for the persistence of pain symptoms. One excellent metaphor for explaining this model is that of a “burglar alarm,” as demonstrated in the following vignette, adapted from Van Wilgen & Keizer (2012, p. 65): Mrs. Johnson, the good news is that there is not anything physically wrong with your jaws (or teeth) that’s causing your pain. But that doesn’t mean that your pain isn’t real or is just “psychological” or anything like that. You see, the human body is like a house. And the pain system in the body is like a burglar alarm. If someone broke into your house, and the alarm went off, you’d probably call the police, right? That would be the sensible thing to do. But let’s say the police come and can’t find an intruder. Then your alarm goes off a second time a few days later and keeps going off every day or so. Would you keep calling the police? Maybe, but you’d probably also check out the alarm itself; maybe it’s broken, or it’s probably set to be too sensitive. This is just like the body in chronic pain. For reasons not well understood, the alarm signal that your jaws (or teeth) send to the brain has become too sensitive and hyperexcitable. After an injury or dental procedure such as a tooth extraction, the tissues and nerves change in response to pain, and become more sensitive as a protective function to allow the injured site to heal and to prevent further damage. For most people, those tissues and nerves return to normal when the injury has healed. But in your case, the nerves are still oversensitive, so it’s like an alarm that keeps going off even when there is no burglar in the house. So even though there’s no new damage, you still have pain. It’s unclear why certain people have nerves that don’t revert to normal after an injury; it may have to do with genetics, and it also appears that more severe injuries create greater sensitization. But the good news is that the kind of sensitivity I’m talking about can be reversed. To return to our metaphor, it’s like you are living in fear of a burglar in your house at every moment, just because the alarm keeps going off. Because you are afraid of doing damage to your jaw, you avoid doing things you used to like to do, and I think you’re tensing your muscles and being very cautious about moving because you’re afraid of more pain. And those are the things I think we should work on, because we know that stress, muscle tension, inactivity, and worry can aggravate pain. We can’t reset the alarm, but we have to learn to ignore it whenever possible, and to go on with life despite it. Psychosocial factors
Basically, when a person acts in a certain manner, reinforcement or punishment can encourage or discourage the behavior. Such reinforcement or punishment leads to changes in behavior. This is what is meant by operant conditioning. Operant conditioning and reinforcement structures have considerable relevance to chronic pain. When a person is in pain, he or she exhibits certain behaviors and says certain things, and how the environment responds to those behaviors may either reinforce or extinguish the person’s pain behaviors. Pain behaviors may be positively reinforced by a number of factors, including attention from family members or from healthcare providers. Pain behaviors may also be negatively reinforced by the reduction of unpleasant states, such as avoiding undesirable activities (e.g., difficult chores or more pain). Also, healthy behaviors (often referred to as well behaviors) such as working, homemaking, engaging in pleasurable activities, and self-care can easily be extinguished if they (a) receive no reinforcement or (b) are associated with more pain. To summarize, the operant model postulates that acute pain becomes chronic because pain behaviors that are normal and adaptive for acute pain (like taking a rest, calling in sick, or having a spouse do all the housework while a person recovers from injury) are reinforced, and therefore never go away, even when the original source of pain has healed or is stable. Classic examples of behaviors and reinforcers in chronic pain are shown in Table 1.
To focus solely on biological factors in chronic pain leaves out some important data on psychological processes, especially in learning and memory, which might help to explain why some people develop chronic pain after injury while others do not. These psychological factors can be labeled in two broad categories: primarily behavioral and primarily cognitive. These groups are separated for clarity of presentation, but in clinical practice these categories overlap and coexist. Behavioral factors There are two major types of learning in animal models: classical conditioning and operant conditioning. Classical conditioning is usually described with the story of Pavlov’s dogs. Ivan Pavlov, a Russian physiologist, rang a bell each time he presented a dog with a tasty treat. As a result, the dogs learned to associate the bell with food and salivated each time they heard the bell, whether Pavlov produced food or not. This kind of learning is strictly associative; nothing the dogs did had an impact on the outcome. But just as important is operant conditioning, a form of learning in which an individual modifies his or her behavior in response to the consequences of that behavior. The learning concepts associated with operant conditioning apply to current understandings of chronic pain.
Table 1: The Roles Of Behaviors And Reinforcers In Chronic Pain Behavior Is the Behavior Helpful for Acute Pain? Is the Behavior Helpful for Chronic Pain?
Response or Result of the Behavior Attention and sympathy.
Reinforcement Type
More or Less Likely to do this Again?
Functional Implications for Chronic Pain
Grimacing, moaning Yes, it communicates pain to engage help.
No, it only confirms that pain is still present.
Positive reinforcement of grimacing/ moaning. Negative reinforcement of guarding.
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More frequent vocalization of pain.
Guarding (avoiding activity due to pain)
Yes, it helps with healing an acute inflammation.
No, it is not helpful because no more healing is possible.
Less pain.
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Less physical activity, more pain, potential weight gain.
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