Psychology 2036A/B Lecture Notes - Lecture 10: Pharmacology, Physical Therapy, Nonsteroidal Anti-Inflammatory Drug

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Chapter 10: PAIN
After reading Chapter 10, you should be able to:
Define and explain chronic pain
Identify and describe three major categories of pain
Identify and describe three factors that explain individual differences in pain
perception
Identify and define three major types of arthritis
Explain ankylosing spondylitis
Identify and define three psychopharmacological therapies for arthritis
Define exercise therapy
Explain the benefits of exercise therapy for people with arthritis
Explain the role of psychological therapies for the treatment of arthritis
Pain is an emotionally aversive subjective experience associated with actual or
potential tissue damage. It is a biological safety mechanism to warn us when
something is physically (organically) wrong. In medicine, it is often referred to as
“the fifth vital sign.” In this lesson we will look at the phenomenon of pain, its
assessment, and its treatment.
THEORIES OF PAIN
Specificity Theories
The earliest specificity theories, going back to Descartes’ dualism and formalized in
1894 by Von Frey, are linear models: injury leads to activation of specific pain
channels in the body, whereby receptors and transmitters send messages along a
particular spinal pathway to a pain center in the brain. The intensity of the stimulus
is said to vary directly with the intensity of the resulting pain. Specificity theories
could not account for cases in which there was no observable organic pathology for
the pain, could not account for the disproportionate relationship between stimulus
intensity and reported pain intensity, and do not allow for psychological or social
factors influencing the experience of pain.
Pattern Theories
Pattern theories were developed to account for non-organic pain. They were based
on the idea that sensory information is transmitted along more than one pathway to
a specific spinal cord location where the information is summed up and, if the
summation exceeds threshold, an impulse is transmitted to the brain and the result
is pain perception. This is not a linear model but it does, unfortunately,
conceptualize the brain as a passive recipient instead of giving it an active role that
involves the influence of psychological processes. Moreover, pattern theories have
difficulty accounting for the effect of placebos on reducing the experience of pain,
and for individual and cultural differences in pain response.
Integrative Theories:
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(i) Gate Control Theory
Developed in the mid-1960s by Melzack and Wall, this theory incorporates the
influence of psychological factors on physiological processes. Pain is now redefined
as a perception, instead of a sensation as was defined in the earlier theories. There is
a “gate” in the spinal column which influences pain fibre transmission. The extent to
which this gate is open or closed determines the degree to which pain fibre
transmission reaches the brain and consequently the degree to which pain is felt.
The gate can be opened or closed by both ascending signals (from pain fibres) to the
brain or by descending signals from the brain (e.g., anxiety). As a result, sensory and
emotional aspects of pain are influenced by the activity of various nerve fibres. The
gate control theory is still basically a physiological model in which physiological and
psychological systems are related, but those systems are not entirely integrated in
enough of a theoretically clear way to be of more explanatory or predictive value.
The theory did however legitimize the value of psychological treatment
interventions for pain. The biggest criticism of the gate control theory is the lack of
physical evidence for a “gate” in the spinal column.
(ii) Neuromatrix Theory
Melzack subsequently extended the gate control theory by increasing emphasis on
the role of the brain, in order to address limitations of the gate control theory. The
neuromatrix now replaces the gate. Pain is believed to be produced by the output of
a widely distributed neural network in the brain, rather than directly by sensory
input evoked by injury or other pathology. One’s neuromatrix is determined by
genetics, experience, and by sensory, cognitive, and emotional factors.
In the following video, Dr. Melzack himself discusses the historical development of
pain theories, from specificity to neuromatrix. REQUIRED video on pain theories:
ACUTE vs. CHRONIC PAIN
Acute: limited duration, lasting less than 6 months.
Chronic: lasting 6 months or more. Back pain is the most common chronic pain
condition.
The 6-month cutoff is for the most part an arbitrary distinction. Acute pain is a
useful biological response evoked by injury or disease. Acute pain generally
responds well to pharmacological treatment. By contrast, chronic pain does not
respond quite as well to pharmacology. Acute pain is considered more of a
symptom, whereas chronic pain is considered more as a disease in its own right. In
addition to length of time it persists, chronic pain also decreases quality of life. It
quite often produces difficulty with falling asleep and staying asleep, as well as
irritability from lack of sleep and from being worn down by the pain. Depression is a
common consequence [more on depression later in this lesson].
Chronic pain can be further specified by the following descriptors:
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