Abstract
Two groups of patients with irritable bowel syndrome rated pain and underwent functional
magnetic resonance imaging brain scanning during experimentally induced rectal distension
(20 seconds, 7 stimuli). Group 1 was tested under baseline (natural history [NH])
and a verbally induced placebo condition, whereas Group 2 was tested under baseline
and standard placebo (no verbal suggestion for pain reduction) and intrarectal lidocaine
conditions. As hypothesized, intrarectal lidocaine reduced evoked pain and pain-related
brain activity within Group 2. Between-group comparisons showed that adding a verbal
suggestion to a placebo condition increased neural activity involved in memory and
semantic processing, areas that process the placebo suggestions. These areas, in turn,
are likely to influence brain areas involved in emotions and analgesia and consequently
the placebo effect. These placebo suggestions also added significant decreases in
activity of brain areas that process pain. The test stimulus itself seems to cue these
effects and is consistent with previous explanations that somatic focus and sensory
feedback reinforce expectations and other factors that mediate placebo analgesic effects.
Perspective
Expectations for pain can be verbally manipulated to produce placebo analgesia. Placebo
analgesia is accompanied by decreased brain activity related to processing pain and
increased brain activity that generates placebo analgesia, including semantic and
memory regions. Placebo suggestions may enhance placebo analgesia by engaging a feedback
mechanism triggered by the painful stimulus itself and related to brain mechanisms
involved in memory and semantic processing.
Key words
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Article info
Publication history
Published online: January 13, 2014
Accepted:
December 23,
2013
Received in revised form:
November 20,
2013
Received:
May 20,
2013
Footnotes
Supported by the National Center for Complementary and Alternative Medicine (R01AT001424, to M.E.R.).
There is no conflict of interest among authors.
Identification
Copyright
Published by Elsevier Inc.
