Two groups of patients with irritable bowel syn
drome rate
d pain an
d un
derwent functional magnetic resonance imaging brain scanning
during experimentally in
duce
d rectal
distension (20聽secon
ds, 7 stimuli). Group 1 was teste
d un
der baseline (natural history [NH]) an
d a verbally in
duce
d placebo con
dition, whereas Group 2 was teste
d un
der baseline an
d stan
dar
d placebo (no verbal suggestion for pain re
duction) an
d intrarectal li
docaine con
ditions. As hypothesize
d, intrarectal li
docaine re
duce
d evoke
d pain an
d pain-relate
d brain activity within Group 2. Between-group comparisons showe
d that a
dding a verbal suggestion to a placebo con
dition increase
d neural activity involve
d in memory an
d semantic processing, areas that process the placebo suggestions. These areas, in turn, are likely to influence brain areas involve
d in emotions an
d analgesia an
d consequently the placebo effect. These placebo suggestions also a
dde
d significant
decreases in activity of brain areas that process pain. The test stimulus itself seems to cue these effects an
d is consistent with previous explanations that somatic focus an
d sensory fee
dback reinforce expectations an
d other factors that me
diate 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.