Pain inhibits pain; human brainstem mechanisms

Conditioned pain modulation is a powerful analgesic mechanism, occurring when a painful stimulus is inhibited by a second painful stimulus delivered at a different body location. Reduced conditioned pain modulation capacity is associated with the development of some chronic pain conditions and the e...

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Bibliographic Details
Published in:NeuroImage (Orlando, Fla.) Fla.), 2016-01, Vol.124 (Pt A), p.54-62
Main Authors: Youssef, A.M., Macefield, V.G., Henderson, L.A.
Format: Article
Language:English
Subjects:
Adult
Analgesia
Analgesics
Animals
Brain Mapping
Brain research
Brain Stem - physiopathology
Brainstem
Diffuse noxious inhibitory control
Female
Functional magnetic resonance imaging
Hot Temperature
Humans
Magnetic Resonance Imaging
Male
NMR
Nuclear magnetic resonance
Pain
Pain - physiopathology
Pain - psychology
Pain Measurement
Pain Perception - physiology
Rodents
Scanners
Spinal cord
Subnucleus reticularis dorsalis
Temperature
Young Adult
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Summary:Conditioned pain modulation is a powerful analgesic mechanism, occurring when a painful stimulus is inhibited by a second painful stimulus delivered at a different body location. Reduced conditioned pain modulation capacity is associated with the development of some chronic pain conditions and the effectiveness of some analgesic medications. Human lesion studies show that the circuitry responsible for conditioned pain modulation lies within the caudal brainstem, although the precise nuclei in humans remain unknown. We employed brain imaging to determine brainstem sites responsible for conditioned pain modulation in 54 healthy individuals. In all subjects, 8 noxious heat stimuli (test stimuli) were applied to the right side of the mouth and brain activity measured using functional magnetic resonance imaging. This paradigm was then repeated. However, following the fourth noxious stimulus, a separate noxious stimulus, consisting of an intramuscular injection of hypertonic saline into the leg, was delivered (conditioning stimulus). During this test and conditioning stimulus period, 23 subjects displayed conditioned pain modulation analgesia whereas 31 subjects did not. An individual's analgesic ability was not influenced by gender, pain intensity levels of the test or conditioning stimuli or by psychological variables such as pain catastrophizing or fear of pain. Brain images were processed using SPM8 and the brainstem isolated using the SUIT toolbox. Significant increases in signal intensity were determined during each test stimulus and compared between subjects that did and did not display CPM analgesia (p
ISSN:1053-8119
1095-9572
DOI:10.1016/j.neuroimage.2015.08.060