Journal
BRAIN BEHAVIOR AND IMMUNITY
Volume 20, Issue 1, Pages 15-26Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.bbi.2005.08.006
Keywords
positron emission tomography; pain; stress; opioid receptors; placebo; human
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Funding
- NATIONAL CENTER FOR COMPLEMENTARY &ALTERNATIVE MEDICINE [R01AT001415] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE ON DRUG ABUSE [R01DA016423] Funding Source: NIH RePORTER
- NCCIH NIH HHS [R01 AT 001415] Funding Source: Medline
- NIDA NIH HHS [R01 DA 016423] Funding Source: Medline
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The activation of pain-suppressive, endogenous opioid neurotransmission after administration of a placebo with expectation of analgesia has been directly demonstrated in humans using molecular imaging techniques in recent work. Regional effects were described in the dorsolateral prefrontal cortex, pregenual anterior cingulate, anterior insula, and nucleus accumbens. However, it was also observed that the magnitude of these responses was subject to substantial individual and regional variation. The present study was undertaken to examine the contribution of various factors to the observed variability in the neurochemical responses to placebo administration. Multiple regression analyses were conducted on data from 19 healthy males to study to what degree expectations of analgesia and various elements of the experience of pain itself, in the absence of placebo, were associated with the individual and brain regional variability in endogenous opioid neurochemical responses to placebo. A model that included affective qualities of pain, the volume of algesic stimulus required to maintain pain over the experimental period within a moderate range, and the internal affective state of the volunteers contributed to 40-68% of the variance in the regional neurochemical responses to placebo. These initial data suggests that in the case of endogenous opioid mediated placebo analgesic responses, the individual experience of pain, in particular its affective elements, the internal affective state of the individuals during pain and a measure of sustained pain sensitivity are important factors contributing to the formation of a placebo effect. Further examination of individual variations in placebo responding will need to take into account the underlying process for which relief is required. (c) 2005 Elsevier Inc. All rights reserved.
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