Purpose: Pain intensity, as intensities of other subjective experiences is challenging to measure. The subjective nature of pain assessment and the variability in how patients are understanding and using pain scales are negatively affecting patient-health care provider communication and reducing the essay sensitivity of pain related studies. Little is known about the ability of patients to accurately report pain, and its possible relations with the ability to accurately report other bodily sensations. The aim of this study was to explore the relationships between the ability to accurately report pain and the ability to accurately report other sensations. Participants and methods: Healthy volunteers enrolled from local universities underwent the FAST procedure, to assess pain reporting accuracy, a taste task, to assess tastes (sweet and salty solutions) intensity reporting accuracy, and the heartbeat perception task, an interoceptive task aimed to assess how accurate subjects are in monitoring and reporting their own heartbeat. In addition, all subjects completed the Multidimensional Assessment of Interoceptive Awareness (MAIA), the Perceived Stress Scale (PSS) and Hospital Anxiety and Depression Scale (HADS). Spearman’s correlations were used to assess relations between the accuracy tasks (FAST and taste) and interoception measures (heartbeat task and MAIA), as well associations with pain-related psychological questionnaires (PSS and HADS). Results: Ability to accurately report the sensations of different modalities were independent of each other (P>0.05 for all outcome measures). Positive correlations were found within modality, between reporting accuracy of salt and sweet solutions (Spearman’s r=0.477, P<0.001). No correlations were found between the psychological and accuracy measures. Conclusion: Pain reporting accuracy is not related to interoceptive awareness of other modalities. Further research is ongoing to investigate the clinical relevance of pain reporting accuracy.

Background: Several studies suggest that exogenous oxytocin nasal spray may enhance placebo analgesia in healthy volunteers and experimental pain models, although the findings remain mixed. The oxytocin placebo hypothesis suggests that increased oxytocin levels trigger a cascade of brain processes that boost positive expectations and augment the placebo response. Since endogenous oxytocin secretion has been found to increase during positive interactions, we hypothesized that changes in endogenous oxytocin levels will affect placebo analgesia in chronic-back-pain patients. Given the role sex has in both placebo analgesia and oxytocin secretion, we hypothesized that the response magnitude will differ by sex. Methods: Chronic-back-pain patients (n = 112) were prospectively recruited and received placebo injections. The placebo response was calculated as the change in the back-pain Visual Analog Score (VAS), and changes between pre- and post-injection salivary oxytocin levels were measured. The effect of sex and changes in oxytocin levels on pain reduction was calculated using two-way analysis of variance (ANCOVA). Results: Oxytocin levels decreased in 62.5% of participants and increased in 37.5%. Increased oxytocin levels were associated with greater pain reduction than decreased oxytocin levels (p = 0.024). Females exhibited greater pain reduction than males (p = 0.034). No interaction between the oxytocin change pattern and sex was observed. Conclusions: This study demonstrates that following a placebo injection, patients suffering from chronic back pain, who exhibited an increase in endogenous oxytocin levels, showed a higher placebo response. Females had a greater placebo response, but this was not associated with an endogenous oxytocin change. These results provide initial support for the oxytocin placebo hypothesis.