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The November issue of the Archives of General Psychiatry reports brain imaging also reveals that during the painful experience, activity then decreases in other areas, including those regions that handle pain modulation.
"The anticipatory brain response may indicate hypervigilance to impending threat, which may lead to increased helplessness and maladaptative modulation during the experience of heat pain," the authors wrote. "This mechanism could in part explain the high comorbidity of pain and depression when these conditions become chronic."
Chronic pain and depression often overlap, the authors wrote. More than 75% of depression patients have recurring or chronic pain, while between 30% and 60% of chronic pain patients also report symptoms of depression.
"Understanding the neurobiological basis of this relationship is important, because the presence of comorbid pain contributes significantly to poorer outcomes and increased cost of treatment in major depressive disorder," they wrote.
The research team, from the University of California, San Diego, in La Jolla, studied 30 adults, half with a major depressive disorder but not on medication for the condition and half without it. All wore devices that could heat their arms to painful levels, and all were given visual signals before the exercise as to whether they would feel painful heat or a more mild warmth.
The patients with depression also completed a questionnaire about their tendencies to magnify, ruminate over or feel helpless in the face of pain.
Compared with the controls, patients with depression showed increased activation in certain areas of their brain, including the right amygdala -- a brain region tied to emotional responses. This increased activity also correlated to higher helplessness scores on the questionnaires of the patients with depression.
"Future studies that directly examine whether maladaptive response to pain in major depressive disorder is due to emotional allodynia [a pain response to a non-painful stimulus], maladaptive control responses, lack of resilience and/or ineffectual recruitment of positive energy resources will further our understanding of pain-depression comorbidity," the authors concluded.
-- Kevin McKeever
SOURCE: JAMA Archives journals, news release, Nov. 3, 2008
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