Fig. 1: Placebo effects on expectancy ratings.
From: Mapping expectancy-based appetitive placebo effects onto the brain in women
All boxplot graphs display the 95% confidence intervals with boxes indicating the interquartile range from Q1 25th percentile to Q3 75th percentile. The gray and black lines indicate medians and whiskers range from minimum to maximum values and span 1.5 times the interquartile range. The dots in the rainclouds above each boxplot correspond to individual participants. Light red corresponds to the decreased hunger suggestion group, gray to control group and blue to the increased hunger suggestion group. a expectancy ratings following the question: How much do you expect the drink to decrease/increase/affect your hunger?, and b for the change in hunger ratings from baseline to the end of the experiment. The hunger ratings were averaged for each participant between three composite ratings addressing hedonic (How pleasant would it be to eat right now?), homeostatic (How much could you eat right now?), and subjective general hunger ratings (How hungry are you right now?). Dots correspond to individual ratings in each group. *p < 0.05. P-values were obtained with two-sampled, two-tailed t-tests. c Pearson’s correlation between expectancy ratings and the change in hunger ratings from baseline to the end of the experiment. Each dot corresponds to a participant in the decreased-hunger suggestion group. The p-value indicates a two-tailed difference from zero correlation. d Statistical parametric maps of significant group level, random effect moderation of brain activation at the time of food choice by expectations about the drink’s effectiveness to decrease hunger (n = 28). Voxels in yellow are displayed for visualization purposes at an uncorrected threshold of p < 0.001, with an extended threshold of k = 44 voxels, which corresponded to pFWE < 0.05 cluster-wise correction for family-wise errors across the whole brain. Activation was taken at the local maxima (MNI x = 6) on the sagittal slice, showing the extent of the activation in mPFC from the superior frontal gyrus to the anterior cingulate cortex. SPMs are superimposed on the average anatomical brain image. Source data and exact p values are provided as a Source Data file.
