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The reproducibility of placebo analgesia.

The reproducibility of placebo analgesia. Debbie Morton Human Pain Research Group. 69 Healthy Volunteers: Two Sessions: Three Experimental Phases. 1) Placebo Group “ You will receive either an inactive cream or a local anaesthetic cream but you will not be told which. ”. Cream.

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The reproducibility of placebo analgesia.

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  1. The reproducibility of placebo analgesia. Debbie Morton Human Pain Research Group

  2. 69 Healthy Volunteers: Two Sessions: Three Experimental Phases 1) Placebo Group “You will receive either an inactive cream or a local anaesthetic cream but you will not be told which.” Cream Pre-cream phase Post-cream phase Conditioning phase placebo group (not told) control group (told) 2) Control Group “You will receive an inactive cream that will have no analgesic effect.” Watson et al. 2006 Pain

  3. Repeatability r = 0.01 r = 0.79

  4. Control distribution Sham treatment distribution 97.5% Threshold individual change in pain - sham treatment group (arbitrary value on y axis) individual change in pain -2 0 2 4 6 - control group Mean change in pain on conditioned arm (pre-post (arbitrary value on y conditioning) 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

  5. Regression model to predict placebo response SE β T-stat P-value Predictors were for the second session only

  6. Dispositional optimism Placebo response in session 1 Expectation of pain relief in session 2 Decrease in state anxiety in session 2 Placebo response in session 2

  7. Pre-cream LEP at Cz Post-cream Placebo Control 1 1 Amplitude µV Amplitude µV ** P<0.05 Time (ms) Time (ms) 2 2 Amplitude µV Amplitude µV ** P<0.05 Time (ms) Time (ms)

  8. The stimulus preceding negativity SPN • Observed during pain anticipation • Late phase has been localised to the an area commonly associated with nociception

  9. Recording the Stimulus Preceding Negativity (SPN) Amplitude µV

  10. Pre-cream Post-cream SPN at CPz Control Placebo 1 1 Amplitude µV Amplitude µV Time (ms) Time (ms) 2 2 Amplitude µV Amplitude µV **p<0.05 Time (ms) Time (ms)

  11. 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

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