the reproducibility of placebo analgesia. debbie morton human pain research group
TRANSCRIPT
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The reproducibility of placebo
analgesia.
Debbie Morton
Human Pain Research Group
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Pre-cream phase Conditioning phase Post-cream phase
placebo group (not told)
control group (told)
1) Placebo Group
“You will receive either an inactive cream or a local anaesthetic cream but you will not be told which.”
2) Control Group
“You will receive an inactive cream that will have no analgesic effect.”
69 Healthy Volunteers: Two Sessions: Three Experimental Phases
Cream
Watson et al. 2006 Pain
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Repeatability
Treatment Group
-2.00
0.00
2.00
4.00
6.00
-2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00
Session 1
Ses
sio
n 2
Control Group
-1.00
-0.50
0.00
0.50
1.00
1.50
2.00
-0.60 -0.10 0.40 0.90 1.40
Session 1
Ses
sio
n 2
r = 0.01
r = 0.79
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-2 0 2 4 6
Mean change in pain on conditioned arm (pre-post
conditioning)
Control distribution
Sham treatment
distribution
97.5% Threshold
individual change in pain
- sham treatment group
(arbitrary value on y
axis)
individual change in pain
- control group
(arbitrary value on y
axis)
Modelling the placebo response
Distributions of the individual mean responses generated using a simple hierarchical model with individual mean responses for the placebo group. The threshold line marks the 97.5th percentile of the control distribution
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Placebo response session 2
No response session 2
Placebo response session 1
13 4
No response session 1
1 20
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State anxiety -0.34084 0.15492 -2.2001 0.035
LOT-R optimism 0.37185 0.15120 2.4593 0.019
β SE T-stat P-value
Regression model to predict placebo response
Predictors were for the second session only
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Expectation of pain relief in
session 2
Dispositional optimism
Placebo response in session 1
Decrease in state anxiety in session
2
Placebo response in session 2
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Control Placebo
1 1
2 2
** P<0.05
** P<0.05
Am
plitu
de µ
VA
mpl
itude
µV
Am
plitu
de µ
VA
mpl
itude
µV
Time (ms)
Time (ms)
Time (ms)
Time (ms)
Pre-cream
Post-cream LEP at Cz
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The stimulus preceding negativity SPN
• Observed during pain anticipation
• Late phase has been localised to the an area commonly associated with nociception
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-3500ms 3000 2500 2000 1500 1000 500 0 PAIN
Am
plitu
de µ
V
Recording the Stimulus Preceding Negativity (SPN)
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Control Placebo
SPN at CPzA
mpl
itude
µV
Am
plitu
de µ
VA
mpl
itude
µV
Am
plitu
de µ
V
Time (ms)
Time (ms)Time (ms)
Time (ms)
1
2 2
1
Pre-cream
Post-cream
**p<0.05
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Conclusions
• The placebo response is reproducible
• Optimism predicts a repeatable response
• A placebo response reduces state anxiety
• The placebo group have a lower post conditioning anticipatory response