Lara Tosunlar, Psychology Research Assistant, Dorset HealthCare NHS Trust
Dr Selwyn Richards, Consultant Rheumatologist, Poole Hospital NHS Trust
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History of chronic pain
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It has long been thought that pain and disability are not only influenced by somatic pathology, if found, but also by psychological and psychosocial factors. However, only recently has the emotional dimension of pain gained salience in pain research (Chapman, 2001). This affective dimension of pain includes both the immediate feelings of unpleasantness associated with the painful sensation and negative emotions evoked by the pain itself (Price, 2000). The consensus that pain is a subjective emotional experience has instigated the study of pain within emotion research (Chapman, 2001). Researchers have since suggested a large overlap between those structures identified as being activated by pain and those associated with emotional responding (Chapman, Nakamura, Donaldson, Jacobson, Bradshaw, Flores and Chapman, 2001; Phan, Wager, Taylor & Liberzon, 2002).
The Gate Control Theory highlighted that pain messages can be directed along a variety of pathways in the brain (Melzack & Wall, 1965). For instance, a “fast” pain message (A-delta fiber) is relayed (at approximately 40mph) by the spinal cord to the thalamus and cerebral cortex in the brain (Ullrich & Burke, 1999). This message quickly reaches the cortex, which is the portion of the brain where higher thinking takes place, prompting immediate action to reduce the pain or potential damage from injury. Alternatively, C-fibers carry electrical messages slowly (approximately 3mph), as in chronic pain, through the spinal cord. Upon reaching the brain, these slow messages move along a different pathway, to the hypothalamus, which is responsible for releasing certain stress hormones in the body and the limbic system, which is responsible for processing emotions. These slow pain signals actually pass through brain areas that control experiences and emotions, which could offer an explanation for why chronic pain is often associated with stress, depression and anxiety.
Pain processing has been compared to the stress response system, with recent literature suggesting they are so interdependent that they should be considered components of a single system (Melzack, 1999). Whether this proves to be true, or they are simply closely interrelated systems, current research clearly demonstrates a strong relationship between pain processing, affective reactivity and the stress response system (Van der Kolk, 1994; Sherman, Turk & Ojifuji, 2000).
Individuals have been found to vary considerably in affective reactivity; whether they are more prone to respond with positive or negative emotions (Davidson, 2000; 2001; 2002). Essentially, individuals who react more quickly and negatively to emotional stimuli are suggested to show a similar response to painful stimuli.
A number of studies have explored the relationships between emotional factors, emotional coping, anger, anxiety, alexithymia, back pain and co-morbid depression (Badura, Reiter, Altmaier, Rhombers, & Bias, 1997; Keefe, Lumley, Anderson, Lynch, Studts, & Carson, 2001). Findings have suggested that emotional difficulties may play a dominant contributory role to a slower recovery in chronic back pain patients (Julkunen, Hurri & Kankainen, 1988). The current research study, discussed in the following section, examined the relationship between emotional processing and pain in a group of chronic pain patients, enrolled in a group therapy intervention programme for their pain.
In a brief summary, emotional processing adds an important angle of thinking to more cognitive explanations. Recent advances in the neurophysiology of pain, involving functional brain imaging of individuals experiencing pain, have highlighted an affective dimension of pain, aside from its sensory aspect. Expression of pain is predominantly emotional and patients with chronic pain often exhibit many affective problems (Okifuji & Turk, 1998). It is becoming increasingly clear that pain and emotional disturbances are interdependent problems, however, limited communication between the fields of pain and emotion research has somewhat hindered developments to date (University of Utah, 2002). By improving communication both domains could benefit and treatment, which tackles both the pain and emotional aspects of chronic pain, could prove to be most effective.