A biobehavioral or a diathesis-stress model of chronic pain needs to con- sider the factors discussed above and their mutual interrelationships in the explanation of chronic pain. The existence of a physiological disposition or diathesis is one important component. This predisposition is related to a re- duced threshold for nociceptive stimulation and can be determined by genetic factors and acquired through early learning experiences. For example, Mogil (1999) showed that large genetic variations in individual pain sensitivity ex- ist. Very impressive evidence for the role of early traumatic experience comes from the work of Anand et al. (1999) who showed that minor noxious experi- ence in neonate rats leads to dramatic alterations (sensitization) in nociceptive processing in the adult organism. A further component of the biobehavioral model is a response stereotypy of a particular bodily system such as exagger- ated muscular responses of the lower back muscle to stress and pain that is based both on the diathesis and on aversive experiences present at the time of the development of the response. These aversive stimuli may include personal or work stress or problematic occupational conditions and will lead not only to painful responses but also to avoidance behaviors and associated maladaptive cognitive and affective processes. The cognitive evaluation of these external or internal stimuli is of great importance in the pain response as discussed above. The focus of the biobehavioral perspective is thus on the patient and not just on the symptoms or the underlying pathology, and this focus also requires that the treatment of the patients be tailored not only to medical factors but that it incorporates psychosocial variables that may often be predominant in states of chronic pain.
Memory for Pain
An important maintaining factor in this chronicity process is the development of central neuroplastic changes or pain memories. These pain-related memo- ries may be explicit (open to conscious awareness) or implicit (not conscious such as habits) and may subsequently guide the patient’s experience and be- haviors. For example, pain patients have a tendency to remember preferentially negative and pain-related life events and show a deﬁcit in the retrieval of posi- tive memories. The experience of
the processing of pain. This expanded cortical representation is accompanied by increased sensitivity to both painful and nonpainful stimuli and may be further enhanced by learning processes or attention to painful stimulation. An even more dramatic example of a learned memory for pain has been found in phantom limb pain patients (Flor et al. 1995). In upper extremity amputees the magnitude of the phantom limb pain was found to be proportional to the amount of reorganization in primary somatosensory cortex, namely, the shift of the cortical mouth representation into the area where the amputated limb was formerly represented. The brain obviously maintains a memory of the former input to the deafferented area and subsequently stimulation stemming from areas adjacent to the deafferented zone elicits sensations and pain in the now absent limb. Phantom pain and cortical reorganization are absent in congenital amputees, suggesting a major role for learning. Neuroplastic learning-related changes outlast the time of nociceptive stimulation and can produce extensive and enduring alterations of nociceptive processing that have to be taken into account in effective treatment planning.
Psychological Treatment of Chronic Pain
Operant Behavioral Treatment
Patients who show high levels of pain behaviors and are incapacitated by their pain should proﬁt from operant behavioral treatment. The goals of this treat- ment are the increase of activity levels and healthy behaviors related to work, leisure time, and family as well as medication reduction and management and the change of the behavior of signiﬁcant others (cf., Fordyce 1976). The overall goal is to reduce disability by reducing pain and increasing healthy behaviors. Medication is switched from a prn basis to a ﬁxed time schedule, where med- ication is given at certain times of the day to avoid negative reinforcement learning from occurring. Similar principles are applied to the enhancement of activity and the reduction of inactivity and invalidity. This approach has been found to be effective in patients with chronic back pain as well as other pain syndromes. Figure 1 shows data on the treatment of ﬁbromyalgia in an operant protocol (Thieme et al. 2003).
Cognitive-Behavioral Treatment of Chronic Pain
The cognitive-behavioral model of chronic pain emphasizes the role of cog- nitive, affective and behavioral factors in the development and maintenance of chronic pain. The central tenet of cognitive-behavioral treatment is to re- duce feelings of helplessness and uncontrollability and to establish a sense of
chronic pain also leads to the development of somatosensory pain memories, for example, an expanded representation of the affected body part in primary somatosensory cortex and other areas related to
Fig. 1 Changes in pain intensity, number of doctor visits, and number of hospital visits in an operant behavioral compared to a standard medical treatment for chronic ﬁbromyalgia syndrome. (Based on Thieme et al. 2003)
control over pain in the patients. This is achieved by the modiﬁcation of pain- eliciting and maintaining behaviors, cognitions, and emotions. The cognitive- behavioral approach teaches patients various techniques to effectively deal with episodes of pain. Pain-related cognitions are changed by cognitive restructur- ing and pain coping strategies such as attention diversion, use of imagery, or relaxation that increase self-efﬁcacy. Several studies have examined the efﬁ- cacy of cognitive-behavioral pain management, which must be considered as a very effective treatment of chronic pain (e.g., Turk and Okifuji 2002).
Biofeedback and Relaxation
Biofeedback refers to the modiﬁcation of a normally nonconscious bodily process (e.g., skin temperature, muscle tension) by making the bodily process perceptible to the patient. The respective physiological signal is measured and ampliﬁed and fed back to the patients by the use of a computer that translates variations in bodily processes into visual, auditory, or tactile signals. Seeing or hearing one’s blood pressure or muscle tension enables a person to self-regulate it. The most common type of biofeedback for chronic pain is muscle tension or electromyographic (EMG) biofeedback, which was found to be effective for several chronic musculoskeletal pain syndromes (e.g., Flor et al. 1992; see Fig. 2). For migraine headache, temperature, blood ﬂow of the temporal artery, or slow cortical potentials have been fed back with good
Fig. 2 Changes in pain intensity after treatment with biofeedback, pseudo therapy, and a standard medical treatment for chronic back pain
results. Similar positive data are available for Raynaud’s disease with respect to temperature feedback. Another respondent method uses various types of relaxation training among which progressive muscle relaxation seems to be especially suited for the treatment of chronic musculoskeletal pain.
Innovative Treatment of Chronic Pain: Changing Pain Memories
The discussion in the preceding sections suggests that the alteration of so- matosensory pain memories might be an inﬂuential method to reduce both chronic musculoskeletal and neuropathic pain. This could be achieved by alter- ing the peripheral input that enters the brain region that coded a pain memory, e.g., by using EMG or temperature biofeedback or by employing a sensory sim- ulation protocol that provides relevant correlated sensory input to the respec- tive brain region. It would also be possible to directly alter the brain response to pain by providing feedback of event-related potential components or EEG rhythms or even blood oxygenation level-dependent changes in functional magnetic resonance imaging (fMRI). Most of these methods have not yet been tested in a systematic manner and their effects on cortical reorganization are so far unknown. Alternatively, pharmacological interventions could be used that prevent or reverse the establishment of central memory traces.
In phantom limb pain, it was assumed that the pain is maintained by cortical alterations fed by peripheral random input. In this case the provision of corre- lated input into the amputation zone might be an effective method to inﬂuence phantom limb pain. fMRI was used to investigate the effects of prosthesis use on phantom limb pain and cortical reorganization. Patients who systemati- cally used a myoelectric prosthesis that provides sensory and visual as well as motor feedback to the brain showed much less phantom limb pain and cortical reorganization than patients who used either a cosmetic or no prosthesis. The relationship between phantom limb pain and use of a myoelectric prosthesis was entirely mediated by cortical reorganization (Lotze et al. 1999). When cor- tical reorganization was controlled for, phantom limb pain and prosthesis use were no longer associated. This suggests that sensory input to the brain region that formerly represented the now absent limb may be beneﬁcial in reducing phantom limb pain. These studies were performed in chronic phantom limb pain patients. An early ﬁtting and training with a myoelectric prosthesis would probably be of great value not only in the rehabilitation of amputees but also in preventing or reversing phantom limb pain.
These assumptions were further conﬁrmed in an intervention study where the patients received feedback on sensory discrimination of the residual limb. Eight electrodes were attached to the residual limb and provided high-intensity
nonpainful electric stimulation of varying intensity and location that led to the experience of intense phantoms (Flor et al. 2001). The patients were trained to discriminate the location or the frequency of the stimulation (in alternating
trials) and received feedback on the correct responses. The training was con- ducted for 90 min per day and was spread over a period of 2 weeks (10 days of training). Compared to a medically treated control group (receiving an equal
amount of attention) the trained patients showed signiﬁcantly better discrimi- nation ability on the stump. They also experienced a more than 60% reduction of phantom limb pain and a signiﬁcant reversal of cortical reorganization with a shift of the mouth representation back to its original location. The alter-
ations in discrimination ability, pain, and cortical reorganization were highly signiﬁcantly correlated.
In a related study asynchronous tactile stimulation of the mouth and hand
region was used over a period of several weeks. This training was based on the idea that synchronous stimulation leads to fusion and asynchronous stimula- tion leads to a separation of cortical representation zones. In this case it was postulated that input from the mouth representation that would now activate the region that formerly represented the now-amputated hand and arm would be eliminated and with it the phantom phenomena that would be projected to the amputated limb. This intervention also showed a reduction in phantom limb pain and cortical reorganization (Huse et al. 2001).
Moseley (2004) used a tripartite program for patients with complex regional pain syndrome (CRPS). This program contained a hand laterality recognition
task (recognizing a pictured hand to be left or right), imagined movements of
the affected hand, and mirror therapy (adoption of the hand posture shown on a picture with both hands in a mirror box while watching the reﬂection of the unaffected hand). After a 2-week treatment, pain scores were signiﬁcantly reduced (see Fig. 3). McCabe et al. (2003) also found a reduction in pain ratings during and after mirrored visual feedback of movement of the unaffected limb in complex regional pain syndrome. These studies suggest that modiﬁcation of input into the affected brain region may alter pain sensation.
Interdisciplinary Treatment Of Chronic Pain
Psychological treatment of chronic pain is usually performed in an interdisci- plinary setting that includes medical interventions, physiotherapy, and social measures that are often combined to a multimodal approach. The problem with multimodal approaches is that some parts of the treatments may counter- act each other and that it is difﬁcult to assess the contribution of the individual components. Rather than combining an array of diverse intervention strategies, it might be more fruitful to aim for a differential indication of various treat- ment components based on pain-related characteristics of the patients. For example, Turk et al. (1998) found that persons characterized by high levels of dysfunction responded better to an interdisciplinary pain treatment program
Fig. 3 Mean (circles) and standard error of the mean (vertical bars) for Neuropathic Pain Scale (NPS) scores for the motor imagery program (MIP) group (ﬁlled circles) and control group (open circles) during the experimental period (weeks 0–12) and after cross-over of the control group (weeks 12–24). MIP consisted of 2 weeks each of recognition of hand laterality (recognition), imagined hand movements (imagined), and mirror movements (mirror). Horizontal bars indicate signiﬁcance (p<0.05) on post hoc Scheffé tests. (From Moseley 2004)
for ﬁbromyalgia syndrome that those who were interpersonally distressed. An- other important aspect of psychological pain management is motivating the patients for a psychological approach. This is often difﬁcult since they may be concerned that the referral to a mental health professional implies that their pain is “not real,” they are exaggerating, the pain they feel is really “all in their head,” or their pain is a psychological and therefore not a physical problem. Furthermore, many pain sufferers fear that a referral for psychological inter- vention implies that they can no longer be helped by the traditional healthcare system and that they are being abandoned as “hopeless cases.” They may view the referral as requiring that they prove that they do have legitimate reasons for their reported symptoms. These people usually believe that psychological assessment is not relevant to their problem, when they know that there must be a known physical basis for their symptoms. The patient may believe that cure of the disease or elimination of the symptoms or physical limitations is all that is required or why they are being referred to a psychologist or psychiatrist. This requires a motivational phase prior to treatment that familiarizes the patients with the multidimensional view of chronic pain and motivates them to view a psychological approach as a chance to alter their attitude toward their pain and a ﬁrst step toward improvement. Interesting new perspectives focus on the combination of behavioral and pharmacological interventions. For example, Dinse et al. (2003) have shown that the effects of sensory dis- crimination training can be enhanced or reduced if the training is combined with amphetamine or an N -methyl-d-aspartate (NMDA) receptor antagonist. Likewise, Ressler et al. (2004) showed that the effects of exposure therapy for aversive fear memories could be enhanced by combining the treatment with a partial NMDA receptor agonist. We are currently testing if the combina- tion of behavior therapy with a cannabinoid treatment is more effective than behavioral treatment alone in the extinction of pain memories.
This chapter focused on the role of learning mechanisms and psychological factors in the development and maintenance of chronic pain. Different psycho- logical treatments of chronic pain were discussed with a focus on innovative treatments of chronic pain designed to change pain memories. Future work should investigate the combination of behavioral and pharmacological inter- ventions. We closed this chapter with an overview of the interdisciplinary treatment of chronic pain.