Individual Differences in Placebo Analgesic Effects

Study Overview
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Brief Summary
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This study examines the effects of placebo suggestions tailored to match or mismatch individual participants' motivational styles-an issue of person-situation 'fit' with important effects in public health settings, but which has been ignored in past research.

Official Title
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Person by Situation Interaction: Matching Suggestions to Participants' Motivational Styles

Conditions
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Healthy

Intervention / Treatment
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* Behavioral: Placebo cream- promotion suggestion
* Behavioral: Placebo cream- prevention suggestion
* Behavioral: Control cream


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Healthy participants Dominant promotion focus or dominant prevention focus (based on our screening) Exclusion Criteria: Currently or recently suffered from chronic pain (based on screening) Cannot tolerate heat pain applied to the forearm, based on a calibration task at the beginning of the experiment

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 55 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: This is a within-participant design. Each participant will participate in two sessions. In both sessions, an over-the-counter hand cream will be applied to their skin, accompanied by a placebo suggestion that the cream is analgesic. In one session, the suggestion will match the participant's motivational style, and in the other session the suggestion will not match their motivational style. The order of sessions will be counterbalanced across participants. Each session will also include a control condition, in which participants will be told that the cream has no affect. The same over-the-counter hand cream will be used in all sessions.
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Placebo<br>All participants will participate in two sessions, one with a placebo suggestion that matches the participant's motivational style, and one with placebo suggestion that does not match their motivational style, in a pseudo-random order. | Behavioral: Placebo cream- promotion suggestion<br>* Over-the-counter hand cream will be applied to participants' skin, but they will be told that they are given a highly efficient topical analgesic cream. The suggestion will be based on a promotion approach (promoting good feelings).<br>Behavioral: Placebo cream- prevention suggestion<br>* Over-the-counter hand cream will be applied to participants' skin, but they will be told that they are given a highly efficient topical analgesic cream. The suggestion will be based on a prevention approach (preventing pain).<br>|
| Experimental: Control<br>Each session will also include a control phase, in which the same cream will be applied, and participants will be instructed that the cream has no analgesic effects. | Behavioral: Control cream<br>* In a control condition, with the same cream as in the placebo interventions, participants will be instructed that the cream is a control cream with no effects.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in subjective ratings of acute thermal pain | Following each thermal stimulus, participants are asked to rate how painful it was, on a semi-circular computerized scale. Ratings are based on the angle (0-180), with higher angle representing higher pain ratings. We will average and compare the pain ratings within participant across interventions. | Measured repeatedly, immediately after thermal stimuli on the day of participation. Averaged and compared across interventions. | 
| Changes in subjective ratings of pain expectations | Before each thermal stimulus, participants are asked to rate how painful they expect the next stimulus to be, on a semi-circular computerized scale. Ratings are based on the angle (0-180), with higher angle representing higher expectations ratings. We will average and compare the expectation ratings within participant across interventions. | Measured repeatedly, immediately before thermal stimuli on the day of participation. Averaged and compared across interventions. | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Facial expressions | We will obtain facial video recordings of participants with a video camera. We will analyze these data according to Facial Action Units (facial expressions) that are known to be related to pain, and compare them across interventions. | Immediate response measured during painful stimulation on the day of participation. Averaged and compared across interventions. | 
| Thermal imaging of the face | We will obtain thermal recordings of participant's face with an infrared camera, and compare the heat signature of the face (the temperature in different parts of the face) across interventions. | Immediate response measured during painful stimulation on the day of participation. Averaged and compared across interventions. | 
| Changes in skin conductance response measured with a Biopac device | Skin conductance will be measured. We will compare the skin conductance response to pain stimuli within participant across interventions. | Immediate response measured during painful stimulation on the day of participation. Averaged and compared across interventions. | 
| Changes in heart rate measured with a Biopac device | Heart rate will be measured. We will compare the heart rate in response to pain stimuli within participant across interventions. | Immediate response measured during painful stimulation on the day of participation. Averaged and compared across interventions. |