GHRL and obesity due to melanocortin 4 receptor deficiency: Several previous studies have examined correlations of postprandial decreases in endogenous plasma ghrelin with changes in food cue reactivity (pictures or taste) or resting BOLD signal with highly variable results, likely related to differences in study design, participant characteristics including obesity status, sample size, assay of total ghrelin or AG, fMRI analysis methods, and statistical thresholds.