Abstract
The hormone oxytocin has been hypothesized to influence the emotional dimension of pain. This randomized, placebo-controlled, double-blind, crossover study explored whether intranasal oxytocin and emotional context can affect heat pain perception in 30 healthy male volunteers. After receiving 36 IU oxytocin or placebo, participants underwent functional Magnetic Resonance Imaging (fMRI) during which noxious and non-noxious thermode heat stimuli were applied. Simultaneously, scenes from the International Affective Pictures System (IAPS) with positive, neutral, and negative emotional valence were shown. Heat intensity and unpleasantness ratings were obtained. The activity of whole-brain correlates of heat processing was quantified via multi-voxel pattern analysis. We observed no appreciable main effects of oxytocin on ratings or neural pain correlates. Effects of emotional picture valence on ratings were smaller than reported in previous studies. Nevertheless, oxytocin was found to significantly enhance the influence of picture valence on unpleasantness ratings at noxious heat levels. No corresponding changes in whole-brain correlates of heat intensity processing were found. Our study provides evidence that intranasal oxytocin increases the effects of emotional context on the subjective unpleasantness of experimental heat pain. Future studies are needed to determine whether this effect can be utilized in clinical settings.
Highlights
Applying the mask to our present fMRI dataset, we found that the resulting multi-voxel heat estimates (MHE) correlated with heat level (r = 0.62, 95% Confidence Intervals (CI) [0.57, 0.66]), as well as intensity (r = 0.64, 95% CI [0.60, 0.68]) and unpleasantness ratings (r = 0.61, 95% CI [0.56, 0.66])
We found that intranasal oxytocin increases the effects of emotional valence on unpleasantness ratings at noxious heat levels (Fig. 3b)
The present study provides evidence that intranasal oxytocin increases the effects of emotional picture valence on subjective measures of heat pain unpleasantness
Summary
In this exploratory, placebo-controlled, double-blind, cross-over trial, 36 participants were recruited and randomly assigned to Group A or B. A fully random allocation sequence was generated by the Center for Clinical Trials at the University of Regensburg According to this sequence, the Hospital Pharmacy of the University of Erlangen labeled and numbered the medication containers. A participant flow-chart and a checklist according to the CONSORT criteria is available online Participants in both groups completed an initial training visit where the testing procedures were practiced outside of the fMRI and without medication applied. A washout-period of ≥7 days between the visits was set to minimize the risk of carry-over effects Under both medication conditions, the effects of factors heat (non-noxious, 44.7 °C and noxious, 47.1 °C) and emotional picture viewing (positive, neutral, negative) were tested during fMRI scanning. Baseline-temperature (35.0 °C) and scrambled picture conditions were assessed as additional control conditions
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