Neural Account of Social Placebo Effect

Study Overview
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Brief Summary
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The current study aimed to reveal the neural mechanism of social placebo belief formation and belief representation, and also investigated how the brain pattern predict the social behavior performance under placebo manipulation.

Detailed Description
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Participants were randomly assigned to spray+ group (sprayed with saline but told as oxytocin) and control group (sprayed with saline but told as saline). After 10 min, participants were invited to the resting-state, text viewing task in fMRI scanner. In resting state session, participants with their eyes open and were instructed to attend to a black fixation cross centrally presented on a grey projection screen for 8 min (240TR). The Text viewing task employed a mixed block and even-related fMRI design. Participants were asked to judge whether they could understand the stimuli or not by a button press (1=understand; 2=not understand). Three kinds of stimuli were presented in separate block including oxytocin-function, oxytocin-knowledge, robot related stimuli, each category contained 20 sentences. In each block, the sentence (within one category) was presented pseudo-randomized from 5s to 9s (with mean duration of 7s), then followed by a jittered time interval (interval time = sentence duration - response time; if participants made response within 5s, the sentence would not disappear until its duration reached 5s). There were two sessions with six blocks per session, and there were 5 sentences (trials) per block. The order of blocks and sentences were designed to present in pseudo-random order and were applied to all participants.

Official Title
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Neural Account of Social Placebo Effect

Conditions
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Spray+ Group, Control Group

Intervention / Treatment
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* Behavioral: spray+ manipulation
* Behavioral: control manipulation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: All participants had normal or corrected-to-normal vision, and mental healthy. Exclusion Criteria: Participants who reported no history of neurological, endocrine or psychiatric disorders, who majored in psychology in college or recently participated in any other drug study were not recruited.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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Male

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
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: spray+ group<br>In spray+ condition, participants learned oxytocin materials on a self-paced basis and then intranasally administered with saline (but it was told as oxytocin). Participants were instructed to refrain from smoking or drinking (except water) for 2 h before the experiment. The spray was administered to each participant three times, and each administration consisted of one inhalation into each nostril. Participants took a rest (they were told it was a time period waiting for treatment to produce effects) for 10min and then performed the experimental tasks. | Behavioral: spray+ manipulation<br>* Participants in spray+ group received placebo manipulation and were told they sprayed was oxytocin (in fact, it was saline);<br>|
| Placebo Comparator: control group<br>In control condition, the materials and procedure were same with the spray+ condition except the nasal spray was told as saline instead. Oxytocin materials used in current experiments were adopted from previous study | Behavioral: control manipulation<br>* Participants in control group were told they sprayed saline (in fact, it was saline).<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The brain functional connectivity | For functional connectivity estimation, we adopted DLPFC, mPFC and reward related brain regions as the seeds to do whole-brain connectivity analysis. And the conducted two-sample T test to examine whether there would be some differences between spray+ and control groups. | 8 mins, 240 TR in scanner | 
| Social brain network properties in resting-state | For the network properties, we chose the social brain network as our target and interested network, then estimated the global efficiency within this network.And the conducted two-sample T test to examine whether there would be some differences between spray+ and control groups. | 8 mins, 240 TR in scanner | 
| The brain response pattern for the key concepts about oxytocin | We estimated the beta response trial by trial for each single concept and then investigated the neural representation of all concepts by using representational similarity analysis (RSA). | 5.33mins, 160TR in scanner | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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social placebo effect, fMRI, neural account