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| 50th Annual Meeting of the American Headache Society |
Boston, Massachusetts June 26-29, 2008 |
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Modulation of Headache Pain |
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BY MAURY M. BREECHER
Contributing Writer |
BOSTON — Learning and cognitive changes
contribute to the development of chronic pain, which
points to the need for early, effective intervention and
for an accurate assessment of patients’ expectations to
improve, said Dr. Howard L. Fields of the University of
California, San Francisco, at the 50th Annual Meeting of
the American Headache Society on June 26.
Dr. Fields explained that migraines can be precipitated
or exacerbated by hunger, certain foods, stress, and
intense sensory stimuli such as noise or bright light.
They can be relieved by mediations including analgesics,
triptans, dopamine antagonists or even placebo, and by
sometimes discontinuing some analgesics. These features
are not explained by the current [theoretical] model in
which headache is initiated and sustained by a
peripheral noxious stimulus.
A new model is called for, said Dr. Fields, that takes
into effect the motivation and learning components of
pain. After all, pain provides the motivation to escape
injury and learning, in the form of experiencing pain,
leads to avoidance of situations likely to produce
injury.
“What is the biological significance of pain?” asked Dr.
Fields.
“All vertebrates, probably all animals can sense
potential tissue damage and respond accordingly, pain is
tissue protective,” he said.
“Biologically there are two important consequences of a
noxious stimulus,” Dr. Fields continued. “One, whenever
a noxious stimulus is applied we immediately want it
stopped, so that is a motivational aspect. If we do
something that makes the pain worse, we learn to not do
it. So pain has a teaching function.”
Dr. Fields reported the proposed new model, the
Motivation Decision Model, encourages doctors to ask,
“How is the suppress decision implemented?
Where the expectation of pain is expected, we are faced
with a conflict, should we go there or not? When faced
with that decision, humans automatically do a
cost-benefit analysis factoring in “How bad was the
pain?” or “How likely is it to occur?”
“We do a cost/benefit analysis,” he added. “We make a
choice. It’s either good or bad. If it’s good, the next
time we are faced this choice, we are more likely to
pursue our goals. If it is painful, we will be less
likely. That, in a nutshell, explains all of human
behavior.”
Dr. Fields said the result of the cost-benefit analysis
is “either you respond to the pain” or you will not
respond. If you respond to the pain, you will experience
greater pain intensity. If the decision is to not
respond to the pain, you actually will feel lower pain
intensity.
So how does the human nervous system suppress the pain?
Scientists now know the neuron pathways that are
involved in the decision not to respond, continued Dr.
Fields.
The discovery of the new opioid receptor and endogenous
opioid agonist, the endorphins, has gone a long way to
helping us understand how humans suppress the urge to
escape from a noxious stimulus, Dr. Fields said. The Mju
opioid receptor implements the suppress pain decision
utilizing what he calls the ascending pain modulation
system. It has its origin in the dorsolateral prefrontal
cortex. Activation of this area has been linked to the
pain modulating pathway. (Science. 2004;303:1161-1167). |
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