The Door Bell Theory, which dates back to 1644, contends that when the “door bell” of pain rings, it means a pain generator is at the door. Well recognized by patients and medical professionals, The Door Bell Theory is likely the most common theory of pain and it is certainly useful in most acute situations. Yet the theory fails to explain much chronic pain, in which there is often no specific injury and no one at the “door,” such as in patients with migraine headaches, fibromyalgia or pain after shingles. Eighty percent of patients with migraines, for example, have no discernible “injury.” Nor does a pain “visitor” always ring the bell. Also, almost everyone has had the experience of cutting themselves, perhaps cooking or gardening, and not realizing it until they see the blood, because they felt no pain. Not too long ago, my wife injured her arm while gardening. X-rays revealed the arm was broken in seven different places yet she reported that her pain on a 1–10 scale was a 2 or 3.

Also, as we have noted elsewhere in this book, there is no one–to–one correlation between pain and injury or pain and abnormalities shown on X–rays and other diagnostic imagery, as this theory would imply. Many or even most chronic pain patients lack a clear injury to explain their pain and a pain generator is seldom disclosed on common medical tests. While X-rays and MRI and CT scans are increasingly used to hone in on the patient’s pain, as well as functional nerve tests and other lab diagnostics, a pain generator is rarely revealed. The dismaying truth about conditions ranging from joint pain, neck pain, headaches, and some spinal conditions to fibromyalgia, complex regional pain syndromes and lower back pain is: the source of the pain is often not identified with today’s sophisticated imagery.

As we saw in the previous chapter, scans often will reveal abnormalities but they are frequently not the pain generator. Patients can end up treated for these identified abnormalities while the source of their pain is not addressed. Patients can also be subject to undue and unnecessary stress when treated for abnormalities that were likely not the cause of their pain. In our current healthcare system, expensive technology is overused, resulting in patients who are overscreened and overdiagnosed for conditions which “nature” and time would likely have resolved. Overscreening is so widespread, patients can feel like they did not receive top medical care if their injury was not X-rayed and given other diagnostic imaging and physicians can cater to this (mis)perception. Such “misattribution” leads to treating the condition shown on the MRI or the X-ray and not the person with pain, as other causes are not evaluated and treated.

As the philosophical pendulum has swung back from a multidisciplinary model of pain to a biological one, clinicians assume there must be underlying disease or a tissue injury when a patient complains of pain or demonstrates “pain behaviors” and they seek a pain generator. This is one of the hazards of unimodal and uncoordinated approaches to pain, versus multidisciplinary care; practitioners treat the pain and not the patient and even “read and treat the X-ray” instead of “reading and treating the patient.” Yet chronic pain can seldom, if ever, be effectively treated without taking into consideration a patient’s psychological, cultural, environmental, social and legal milieu.

The Gate Theory was considered revolutionary when described in 1965 by Melzack and Wall. It proposes that stimulation of innocuous neural pathways, carried on the large myelinated A-fibers can block concurrent noxious information carried from the smaller, C- fibers. Signals from the A-fibers, carrying information about touch, temperature, pressure, and electrical sensations, can “close the gate” on the C-fibers which carry pain messages to the spinal cord and then to the brain, by preempting them, according to this theory. It is postulated that this happens through direct inhibition of pain transmission in the dorsal horn of the spinal cord and possible recruitment of endogenous inhibitory pathways through the columns of the spinal cord.

We now know that emotional states like anxiety, depression, frustration, fear, and anger (often related to a work injury or car accident) usually open the “gates.” Conversely, the gate is often “closed” by exercise, heat, cold, pressure, psychological approaches such as Cognitive Behavior Therapy (CBT), Acceptance and Commitment Therapy (ACT), relaxation and stress reduction techniques and some medications. Electrical stimulation, whether peripheral stimulation such as transcutaneous electrical nerve stimulation (TENS) or spinal cord stimulation (SCS) are also known to close the gate, as are psychological techniques such as relaxation, positive thinking and mind-body techniques. Many of these techniques are discussed in Chap. 4, about Cognitive Behavioral Therapy (CBT) techniques.

Central to the Mismatch Theory is that when the brain is continually told to overcome pain recognition and the pain cannot be overcome, the patient experiences anxiety, frustration, anger, helplessness, and hopelessness. We often see that aggregation of emotions in patients with many chronic pain conditions, especially those with fibromyalgia, where there is a “sensory amplification” leading to a wide spectrum of symptoms not explainable by pathological nociception.

One alternative chronic pain treatment that employs the Mismatch Theory is Mirror Therapy. In one study at Bath Royal National Hospital for Rheumatic Diseases, healthy volunteers seated in front of mirrors that made them look symmetrical, hiding one arm, were asked to move their arms on the basis of their reflection, creating a “mismatch” between the actual motion and mirror motion (Vince 2005). “Almost instantly they began to feel sensations in the arm they couldn’t see,” said Candy McCabe of the University of Bath in the United Kingdom. Under this theory, subjects’ brains were “correcting” the mismatch.

In another study, eight patients with Complex Regional Pain Syndrome (CRPS) were seated in front of mirrors such that their painful limb was occluded and they appeared to have two health arms. After being instructed to “try to believe” the mirror depiction, patients experienced pain relief, in some cases, instantly. When the mirror was removed, the pain returned, said researchers. CRPS is discussed in depth in Chap. 10 of this book.

The Loeser Model of pain, proposed by John Loeser of the University of Washington, Seattle more than three decades ago, construes the pain experience as four layers, seen in Fig. 3.1 and Table 3.3, or “onion rings,” which move outward from physical factors to behavioral factors.

At the center Loeser’s “onion” are the physiological factors of nociception as described in the Door Bell Theory. Yet, as the layers move outward, the pain experience becomes increasingly subjective from the actual quality of pain that patients try to share with us to their interpretation of the sensations (“Suffering”) and their bodily responses (“Pain Behavior”).

At the heart of Loeser’s theory is the recognition that, while a patient’s pain may not be resolvable, his behaviors can lessen his pain if the patient is willing and able to replace them with “well” behaviors. This constitutes the goal of therapy under the Loeser model—to decrease the suffering and pain behaviors—and replace them with “well behaviors.”

Loeser’s theory also acknowledges that the degree of suffering a patient’s experiences often encompasses his predictions of what the pain “means” medically, and is also affected by his culture. For example, patients know that pain after they exercise and certainly during childbirth is “normal.” Yet other pain is often regarded as harmful, especially if it is unfamiliar. It is important that we explain to patients the difference between “hurt” (which implies pain) and “harm” (which implies further damage or injury) as we noted in the last chapter.