No evidence that attentional bias towards pain-related words is associated with verbally induced nocebo hyperalgesia: a dot-probe study

Introduction: Placebo and nocebo effects in pain are well documented. One leading explanation is that instructions indicating that pain will either increase or decrease after receipt of a treatment give rise to expectations for increased or decreased pain. However, the psychological mechanisms through which expectations affect pain perception are not well understood. One possibility is that the expectation of increased pain leads to anticipatory anxiety, which in turn increases attention towards painful sensations. Objectives: The aim of this study was to test the hypothesis that attention mediates nocebo hyperalgesia. This was done by measuring attentional bias towards pain using a dot-probe task both before and after a nocebo manipulation. Methods: Ninety-six healthy volunteers were randomized to receive one of the following: (1) an inert nasal spray with placebo instructions, (2) an inert nasal spray with nocebo instructions, or (3) no treatment. Participants completed measures of expectations, anxiety, and attention bias (dot-probe paradigm) both before and after randomization. Results: Results showed that the nocebo instructions induced expectations for increased pain and resulted in nocebo hyperalgesia. Conversely, the placebo instruction failed to induce expectations for decreases in pain and did not demonstrate any placebo analgesia. Furthermore, despite the significant expectancies for pain and subsequent nocebo hyperalgesia, there were no differences between the nocebo group and either the placebo or no-treatment group for anxiety or attentional bias. Conclusion: The results are consistent with the expectancy model of placebo and nocebo effects. That is, changes in expectations seemed to be necessary to induce a placebo or nocebo effect. However, there was no evidence that anxiety or attention bias towards pain-related stimuli was necessary to achieve nocebo hyperalgesia.