Our readings and video for this week highlight the biological aspects of pain perception and modulation. After reviewing the course lecture, reading the selected articles, and viewing the gate control theory of pain video, post your answer to the following questions on this discussion board:
1). In your opinion, why is it important for mental health practitioners to have an understanding of the biological factors that influence pain experiences?
2). Also, imagine that you are a provider who wishes to explain the gate control theory of pain to an adult or pediatric patient. Write a brief 'script' for how you might go about presenting this information in a patient-friendly format and include a rationale for why their engagement in psychosocial pain management strategies might assist them in better coping with their acute or chronic pain.
An Introduction to Understanding & Managing Pain
+ The Somatosensory System
n Pain and the Nervous System n All sensory stimulation, including pain, starts with activation of sensory neurons and proceeds
with the relay of neural impulses toward the brain.
n Somatosensory System n The somatosensory system conveys sensory information from the body through the spinal
cord to the brain. n Afferent Neurons
n Afferent (sensory) neurons convey sensory information from sense organs to the spinal cord and then to the brain. Efferent (motor) neurons result in the movement of muscles. Interneurons connect afferent and efferent neurons. Primary afferents are those neurons that have receptors in the sense organs and that originate the neuron’s message. The vast number of neurons and their interconnections makes neural transmission complex.
n Involvement in Pain n Nociceptors are neurons capable of sensing pain stimuli. Three different types of
neurons are involved with transmitting pain impulses. The large A-beta fibers and smaller A-delta fibers are covered with myelin, which speeds neural transmission. The smaller and more common C fibers require high levels of stimulation to fire. These different fibers with their different thresholds and transmission speeds may relate to different types of pain sensation.
+ The Spinal Cord
Cross Section of the Spinal Cord: The spinal cord is a pathway for ascending sensory information and descending motor information to and from the brain
+ The Somatosensory Cortex
v From the spinal cord, the brain receives informa5on from afferent neurons
v The Somatosensory
cortex is the part of the brain that receives sensory informa5on that allows the en5re surface of the skin to be mapped
+ The Spinal Cord & Brain (Continued) n Primary afferents from the skin enter the spinal cord where they synapse with neurons in
the dorsal horns of the spinal cord.
n The dorsal horns contain several laminae (layers). Laminae 1 and laminae 2 form the substantia gelatinosa, a structure that receives sensory input from the A and C fibers.
n Complex interactions of sensory input occur in the laminae of the dorsal horns, and these interactions may affect the perception of sensory input before it gets to the brain.
n In the brain, the thalamus receives sensory input from the different neural tracts in the spinal cord.
n The skin is mapped in the somatosensory cortex in the parietal lobe of the cerebral cortex, and the proportion of cortex devoted to an area of skin is proportional to that skin’s sensitivity to stimulation.
n Sensory information from internal organs are not mapped as precisely as the skin, leading people to have the ability to identify stimulation from the skin but less distinct sensory perceptions of their internal organs.
n This is also the reasoning behind referred pain, when pain is experienced in a part of the body other than the site where the pain stimulus originates.
+ Neurotransmitters & Pain n The neurotransmitters that form the basis for neural
transmission also play a role in pain perception.
n The discovery of the endogenous opiates—enkephalin, endorphin, and dynorphin—led to the discovery of neural receptors specialized for these neurotransmitters and the conclusion that opiate drugs produce analgesia because of the brain’s own chemistry.
n The neurotransmitters glutamate and substance P and the chemicals bradykinin and prostaglandins may exacerbate pain stimulation.
n Proinflammatory cytokines produced by the immune system are also involved in pain, possibly creating chronic pain by sensitizing neurons in the spinal cord.
The Modulation of Pain
Descending pathways from the periaqueductal gray prompt the release of endogenous opiates (endorphins) that block the transmission of pain impulses to the brain.
+ The Meaning & Definition of Pain n The traditional view of pain focused on the physical sensations, but
about 100 years ago, C. A. Strong proposed that pain consists of not only the sensation but also person’s reaction to that sensation.
n Definition of Pain n Perhaps the most acceptable definition of pain is the one proposed by the
International Association Subcommittee for the Study of Pain that defined pain as an unpleasant sensory experience accompanied by an emotional experience and actual or potential tissue damage.
n At least three stages of pain have been identified: n Acute pain is ordinarily adaptive, lasts a relatively short period of time,
and includes pain from cuts, burns, and other physical trauma. n Chronic pain endures beyond the time of normal healing, is relatively
constant, is often reinforced by other people, and may become self- perpetuating.
n Prechronic pain is experienced between acute and chronic pain and is critical because during this time, the pain may either go away or evolve into chronic pain.
n Another type of pain is chronic recurrent pain, or when there are alternating episodes of intense pain and no pain.
+ The Experience of Pain n Pain is both personal and subjective, but situational and cultural factors play a
role in its experience.
n Beecher’s observations on wounded soldiers during World War II highlight the variability of pain—seriously wounded soldiers reported little pain. n Individual variations exist in the experience of pain, but as Beecher
suggested, situational factors are important. n Cultural expectations and stereotypes as well as cultural sanctions against
the expression of pain influence pain behaviors. n Sanctions against expressing pain may be a large part of the gender
difference in pain, but some evidence indicates that women may also be more sensitive to pain.
n Thus, a variety of individual, cultural, and gender-related factors influence the experience of pain. n Cultural Differences in Pain: African Americans and Hispanic
Americans show higher sensitivity to pain than European Americans n Gender Differences: Women report pain more readily than men (maybe
do to socialization and gender roles).
+ Theories of Pain: Specificity Theory
n How people experience pain is the subject of a number of theories.
n Of the several models of pain, two capture the divergent ways of conceptualizing pain: the specificity theory and the gate control theory.
n Specificity Theory n The specificity theory can be traced to Descartes, who
hypothesized that the body works by mechanistic principles. Applied to pain, this theory holds that pain is the result of transmission of specific signals. Research has failed to find pain receptors or fibers specifically devoted to pain transmission. This theory also fails to integrate the variability of the pain experience.
+ Theories of Pain: �
Gate-Control Theory n Melzack and Wall formulated the gate control theory of pain as a
way to explain the variability of pain perception.
n They hypothesized that a gating mechanism exists in the spinal cord and that sensory input is modulated in the substantia gelatinosa of the dorsal horns of the spinal cord.
n This modulation can change pain perception, as can brain-level alterations from a hypothesized central control trigger.
n This theory includes explanations of both physiological and psychological modulations of the pain experience.
n Melzack has proposed an extension to the gate control theory, called neuromatrix theory, which places a stronger emphasis on the brain’s role in pain perception.
+ Gate-Control Theory of Pain
+ Gate Control Theory (Continued)
n Gate Control Theory also suggests that pain has motivational and emotional components
n Gate control trigger n Nerve impulses that descend from the brain and
influence the gate mechanism n For example, distraction or relaxation could
cause the gate to close, causing a decrease in pain
+ Measurement of Pain
n Tools for measuring pain are important in order to evaluate the various pain therapies.
n A number of techniques have been used to measure laboratory and clinical pain, and these fall into three main categories n Self-reports, n Behavioral assessments n Physiological measures
+ Measurement of Pain: Self-Report n Self-reports of pain include:
n Simple rating scales n Standardized pain inventories n Standardized personality inventories
n Rating Scales n With self-report rating scales, patients rate the intensity of their pain
on a scale; for example, the scale may range from 1 to 100. n A similar technique is the Visual Analog in which patients check
severity of pain on a continuum from no pain to worst pain imaginable.
n The faces scale is a similar approach consisting of drawings of facial expressions of pain, which is suitable for children and older adults.
+ Self-Report Measures (Continued) n Pain Questionnaires
n McGill Pain Questionnaire (MPQ) n Melzack developed the McGill Pain Questionnaire (MPQ), an inventory that categorized pain into
three dimensions: sensory, affective, and evaluative. n The sensory dimension includes pain described in terms of its temporal, spatial, pressure, and
thermal properties. n The affective dimension defines pain in terms of fear, tension, and autonomic properties of the
pain experience. n The evaluative dimension includes the perceived severity of the entire pain experience. The MPQ
has adequate validity, but its vocabulary is somewhat difficult.
n The Multidimensional Pain Inventory (MPI) n The MPI is another questionnaire that measures several aspects of pain: characteristics of the
pain, patients’ perception of the responses of others to their pain, and ratings of daily activities of the patient. This inventory has allowed for the development of 13 different scales that capture different dimensions of the lives of pain patients.
n Standardized Psychological Tests
n Standardized tests, such as the MMPI-2, have also been used to assess pain. This instrument is useful in differentiating among types of pain patients and has some ability to predict which patients will respond to medical treatments for pain. Other commonly administered tests include the Beck Depression Inventory and the Symptom Checklist-90.
+ Behavioral Assessment Tools n Behavioral assessments of pain use observation of the patient to
assess pain n Record body movements and facial expressions
looking for signs of pain n This method may be especially useful for children and
elderly who may not be able to accurately self-report on pain
n People in pain often behave in ways that communicate to others that they are in pain, which can be used as an informal or standardized assessment of pain
n Health care workers tend to underestimate patients’ pain, but spouses and others close to pain patients can provide a better assessment
n This approach is especially useful for individuals who cannot provide self-reports, such as small children and some older individuals who cannot communicate verbally
+ Physiological Measures n Although pain produces an emotional response, research has
failed to identify specific organic states that are strongly correlated with pain.
n Muscle tension and autonomic responses such as heart rate and skin temperature show some relationship to the experience of pain, but neither type of measurement shows sufficient reliability and validity to be a good measurement technique.
n Overall, physiological assessments may not be as valid as self- report or observational methods.
n Physiological Measures include: n Electromyography (EMG) – measures level of muscle
tension, as pain may increase tension n Heart rate – predicts perception of pain, but only for
+ Pain Syndromes
n Acute pain has the advantage of signaling injury, but chronic pain has no advantages.
n Such pain can be classified according to location or syndrome, symptoms that occur together and characterize a condition.
n Headache and low back pain are the two most frequently treated types of chronic pain, but health psychologists also deal with other pain syndromes.
+ Pain Syndromes: Headache n Headache pain is the most common of all pains, with more
than 99% of Americans suffering from some form of headache over their lifetime.
n The most common varieties are migraine, tension, and cluster headaches, although the symptoms overlap and clear classification is often impossible. n Migraine (or vascular) headaches bring about loss of appetite,
nausea, vomiting, and increased sensitivity to light. n Tension headaches are muscular in origin and are characterized
by contractions of the muscles of the neck, shoulders, scalp, and face.
n Cluster headaches produce intense pain localized in one side of the head and occur frequently over a period of days, thendisappear for weeks or months.
+ Pain Syndromes: Lower Back Pain
n The most frequent causes of low back pain are injury or stress resulting in musculoskeletal, ligament, or neurological problems in the lower back.
n In addition, stress and psychological factors may play roles in back pain.
n Most of the people who experience back pain do not progress to chronic pain, but those who do tend to have persistent pain.
n Only about 20% of back pain patients have an identified, physical cause for their pain.
+ Pain Syndromes: Arthritis Pain
n A variety of arthritic pains exist, and many involve inflammation of the joints.
n Rheumatoid arthritis, perhaps the most frequent cause of arthritic pain, is an autoimmune disorder characterized by a dull ache within or around a joint.
n Osteoarthritis is a progressive inflammation of the joints mostly affecting older people and characterized by a dull ache in the joint area.
n Fibromyalgia is a chronic pain condition characterized by tender points throughout the body, fatigue, headache, cognitive difficulties, anxiety, and sleep disturbances. n This condition leads to a diminished quality of life that is similar to the
barriers faced by those with arthritis.
+ Pain Syndromes: Cancer Pain
n Cancer pain has 2 causes: n A malignancy n The treatment of a malignancy
n Approximately 44% of cancer patients report cancer/cancer- treatment-related pain
n Pain is present in a majority of terminal cancer cases, and both chemotherapy and radiation therapy produce pain
n Often pain goes untreated for cancer patients
+ Pain Syndromes: Phantom Limb Pain
n Phantom limb pain is the experience of chronic pain in an amputated part of the body.
n People who have had arms, legs, or breasts removed nearly always continue to feel some sensation (frequently pain) despite the removal of that body part and the nerves that underlie sensation.
n Reports vary but it may be that 90% of amputees experience phantom limb pain.
n Pain is more likely to occur when a person experienced much pain before the amputation.
n There may be an emotional basis to this pain but also the CNS and PNS may make maladaptive adaptations after the amputation.
+ Managing Pain
n Treatment for pain varies n Acute pain is easier to treat as the source of the
pain is clear n Chronic pain is more difficult because there is not
usually an obvious source n Relief can be sought by two methods:
n Medical approaches n Behavioral management approaches
+ Pain Management: Medical Approach
n Treatment of acute pain is easier than for chronic pain, but both present challenges.
n Analgesic drugs n They are the most common treatment for acute pain n These drugs fall into two groups: opiates and nonnarcotic analgesics.
n Opiate drugs have powerful analgesic effects but also produce tolerance and dependence. However, the fear of drug-related problems, such as addiction, leads to under-medication more often than to drug abuse. The recent increase in the use of prescription analgesic drugs was due mostly for the demand for oxycodone and hydrocodone, both of which are opiates with a potential for abuse. Low back pain patients may receive more drug treatment than the ideal level for their condition.
n Aspirin and the other nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen sodium, as well as acetaminophen drugs, are all useful in managing minor pain, especially pain due to injury. Antidepressant drugs and antiseizure drugs also affect pain perception and may be useful in pain management for some people.
+ Medical Approach (Continued)
n Surgery n Surgery may be directed either to repairing damage that causes
pain or to altering the nervous system to change pain perception. n Surgery is an attempt to control low back pain more often than
other pain syndromes, and specific nerves or the spinal cord may be targets.
n Surgery may also be used to implant devices to stimulate the spinal cord to decrease pain. n Surgery is not always effective, either in repairing damage or in
producing pain relief, especially for people with low back pain. n A related technique is transcutaneous electrical nerve
stimulation (TENS), which uses electrical impulses to stimulate skin stimulation to block pain messages. n Spinal cord stimulation is more effective than TENS.
+ Behavioral Approaches
n Some people classify behavioral techniques as alternative treatment or mind-body medicine, but psychologists focus on the behavioral aspects of these treatments and consider them part of psychology.
n Several behavioral approaches have been used to help manage pain:
n Relaxation therapy n Behavioral therapy n Cognitive therapy n Cognitive-behavioral therapy
+ Behavioral Approaches: Relaxation
n Relaxation Therapy involves the systematic tensing and relaxing of muscles n It is used successfully to treat tension and migraine headaches,
rheumatoid arthritis, low back pain
n Progressive muscle relaxation (PMR) involves learning to relax the entire body, one muscle group at a time, and to breathe deeply and exhale slowly n This technique had been used to manage a variety of pain
problems, including headaches, rheumatoid arthritis, and low back pain.
n A National Institutes of Health Technology panel’s evaluation for pain treatments gave relaxation training its highest rating.
+ Behavioral Therapy n Behavior modification techniques are based on the principles of operant
conditioning and are used by health psychologists to help people cope with stress and pain.
n The goal of behavior modification is to shape behavior, not to alleviate feelings of stress or sensations of pain.
n People in pain may continue their pain behaviors because they receive positive reinforcers such as attention, sympathy, financial compensation, relief from work, and other rewards.
n Positive reinforcers may create pain traps that turn acute pain into chronic pain.
n The rationale behind behavior modification is to train people in the pain patient’s environment to discontinue reinforcement for pain behaviors, thus avoid the pain trap.
n Progress is measured in terms of observable behavior, such as amount of medication, absences from work, physical activity, and so forth. Behavior modification does not address the cognitions that underlie behavior.
+ Cognitive Therapy
n Cognitive therapy rests on the assumption that a change in the interpretation of an event can change people's emotional and physiological reaction to that event. n It is based on the principle that people’s beliefs, personal
standards, and feelings of self-efficacy strongly affect their behavior.
n Because pain is at least partially due to psychological factors, cognitive therapy attempts to get patients to think differently about their pain experiences and to increase their confidence that they can cope with them. n A goal of treatment is to identify irrational thoughts or “catastrophizing” and eliminate or change them.
+ Cognitive-Behavioral Therapy (CBT) n CBT aims to develop beliefs, thoughts, and skills to make
positive changes in behavior.
n Dennis Turk and Donald Meichenbaum have developed a cognitive behavioral program for pain management called pain inoculation, which parallels stress inoculation. n These techniques involve the cognitive stage of
reconceptualization and the behavioral stages of acquisition and rehearsal of skills and follow-through.
n One form of CBT is acceptance and commitment therapy (ACT) which encourages acceptance of pain by focusing attention on other valuable goals and activities.
n Research indicates that behavior modification, cognitive therapy, and cognitive behavioral therapy are effective for a wide variety of pain conditions.
n The Pain sensation and perception process is a complex one involving skin reception, the spinal cord, and the brain’s somatosensory cortex. In addition, pain perception may be modulated by neurochemicals and periaqueductal gray.
n Pain is difficult to define but it can be classified as acute, chronic, or pre-chronic.
n The personal experience of pain is affected by multiple factors.
n There are multiple types of pain measurements including physiological, observational, and self-report tools.
n Pain syndromes are a common way of classifying chronic pain according to pain symptoms
n Relaxation, behavioral, and cognitive-behavioral techniques are effective for pain management
Psychological Pain Interventions and Neurophysiology
Implications for a Mechanism-Based Approach
Herta Flor Central Institute of Mental Health, Mannheim, Germany, and Heidelberg University
This article provides an illustrative overview of neurophys- iological changes related to acute and chronic pain involv- ing structural and functional brain changes, which might be the targets of psychological interventions. A number of psychological pain treatments have been examined with respect to their effects on brain activity, ranging from cognitive- and operant behavioral interventions, medita- tion and hypnosis, to neuro- and biofeedback, discrimina- tion training, imagery and mirror treatment, as well as virtual reality and placebo applications. These treatments affect both ascending and descending aspects of pain pro- cessing and act through brain mechanisms that involve sensorimotor areas as well as those involved in affective- motivational and cognitive-evaluative aspects. The analy- sis of neurophysiological changes related to effective psy- chological pain treatment can help to identify subgroups of patients with chronic pain who might profit from different interventions, can aid in predicting treatment outcome, and can assist in identifying responders and nonresponders, thus enhancing the efficacy and efficiency of psychological interventions. Moreover, new treatment targets can be de- veloped and tested. Finally, the use of neurophysiological measures can also aid in motivating patients to participate in psychological interventions and can increase their ac- ceptance in clinical practice.
Keywords: neurophysiological, pain, psychological treat- ment, magnetic resonance imaging
Psychological treatments for chronic pain include alarge variety of cognitive-behavioral interventionsranging from biofeedback to pain management training to hypnosis. In general, these interventions have been shown to be successful, with effect sizes in the me- dium to high range (Williams, Eccleston, & Morley, 2012). In recent years, more information has become available about the structural and functional brain changes that are related to pain (for a review, see Davis & Moayedi, 2013), and successful treatments should reverse these changes. It will be interesting to see whether and how these assess- ments can help in designing better treatment interventions. Moreover, only a few studies have examined which com- ponents of these often very broad treatment approaches are effective and how they affect brain function and peripheral physiological responses. In this overview I first describe typical brain changes associated with the experience of
acute and, especially, chronic pain and then discuss how psychological interventions might impact them. Finally, I outline areas of future research and discuss how neurophys- iological examinations can help provide a better under- standing of chronic pain and aid in the development of new and more refined psychological treatments.
Neurophysiological Characteristics of Acute and Chronic Pain There are numerous brain changes that have been associ- ated with acute and chronic pain. In acute pain, functional magnetic resonance imaging (fMRI) revealed regions such as the anterior cingulate cortex (ACC), the amygdala, the periaqueductal gray, the anterior insula, and the nucleus accumbens to be associated with affective and motivational processing; the primary (S1) and secondary (S2) somato- sensory cortex, the posterior insula, and the thalamus with sensory processing; and frontal areas, including the ACC, with the cognitive modulation of pain (cf. Apkarian, Hashmi, & Baliki, 2011). In addition, social and other context variables such as learnt associations with pain or social reinforcement and empathy can affect how nocice- ptive stimulation will be processed by the brain and turned into a pain experience. Here, not only is activation in certain brain areas important, but multiple networks may interact at any given point in time and contribute to several aspects of pain. In addition, not only do these regions seem
Editor’s note. This article is one of nine in the February–March 2014 American Psychologist “Chronic Pain and Psychology” special issue. Mark P. Jensen was the scholarly lead for the special issue.
Author’s note. This research was supported by the Award for Basic Research of the State of Baden-Württemberg, Germany; the PHANTOMMIND project (“Phantom Phenomena: A Window to the Mind and the Brain,” which receives research funding from the European Community’s Sev- enth Framework Programme, FP7/2007-2013/ERC Grant Agreement 230249); and the research Consortium LOGIN (“Localized and General- ized Musculoskeletal Pain: Psychobiological Mechanisms and Implica- tions for Treatment”), funded by the German Federal Ministry of Educa- tion and Research (01EC1010D). This manuscript reflects only the author’s views, and the European Community is not liable for any use that may be made of the information contained therein.
Correspondence concerning this article should be addressed to Herta Flor, Department of Cognitive and Clinical Neuroscience, Central Insti- tute of Mental Health, Square J5, D-68159 Mannheim, Germany. E-mail: [email protected]
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