Nocebo hyperalgesia can be induced by classical conditioning without involvement of expectancy

Influential theoretical accounts take the position that classical conditioning can induce placebo effects through conscious expectancies. In the current study two different conditioning procedures (hidden and open) were used to separate expectancy from conditioning in order to reveal the role of expectancy in the formation of nocebo hyperalgesia. Eighty-seven healthy females were randomly assigned to three groups (hidden conditioning, open conditioning, and control). Participants were selected according to the Fear of Pain Questionnaire scores and assigned to two subgroups: high and low level of fear of pain (trait). They received electrocutaneous pain stimuli preceded by either an orange or blue color. During the conditioning phase, one color was paired with pain stimuli of moderate intensity (control stimuli) and the other color was paired with pain stimuli of high intensity (nocebo stimuli) in both hidden and open conditioning groups. Only participants in the open conditioning group were informed about this association, however just before the testing phase the expectancy of hyperalgesia induced in this way was withdrawn. In the control group, both colors were followed by control pain stimuli. During the testing phase all participants received a series of stimuli of the same intensity, regardless of the preceding color. Participants rated pain intensity, expectancy of pain intensity and fear (state). We found that nocebo hyperalgesia was induced by hidden rather than open conditioning. The hidden conditioning procedure did not produce conscious expectancies related to pain. Nocebo hyperalgesia was induced in participants with low and high fear of pain and there was no difference in the magnitude of the nocebo effect between both groups. Nocebo hyperalgesia was not predicted by the fear of upcoming painful stimuli

Is pain contagious? : innocuous stimulation can be transformed into the pain experience by observational learning

Studies indicate that classical and operant conditioning have potential to play a role in the formation of the allodynic effect. Only a few studies have examined the role of observational learning in pain induction. Due to some methodological challenges, evidence that the allodynic effect can be learned through observation is limited. In the present study, healthy participants (n = 88) received 2 series of innocuous electrocutaneous stimuli: at the beginning of the study and after observation of a model who rated all the stimuli as painful. Participants and the model rated all the stimuli alternately (real-time group), or the participant first observed the model and then rated the stimuli, while the model stayed in (post-hoc+ group) or left (post-hoc- group) the laboratory. There was no model in the control group. The study demonstrated that allodynia can be induced by observational learning. Fur thermore, this effect was shown to be similar, regardless of whether stimuli were received during the observation of the model and rated immediately afterwards, or when the observation and stimuli reception were time-separated. The mere presence of the model during the stimuli reception also did not affect the magnitude of this effect. This research may contribute to our understanding of the mechanisms of chronic pain development and assist in the development of suitable treatment for it. Perspective. This article presents study results on the role of observational learning in allodynia induction without tissue injury. The results may contribute to our understanding of the mechanisms of chronic pain development and assist in the development of suitable treatment for it

The Anaesthetic Context: Placebo Effects and the Experience of Pain (the Psychological Aspect)

Intensywnie prowadzone w ostatnich latach badania nad działaniem placebo doprowadziły do rozwoju kilku propozycji teoretycznych dotyczących jego mechanizmów. Celem artykułu jest podsumowanie i krytyczna dyskusja aktualnego stanu badań nad działaniem placebo w badaniach nad bólem i w praktyce klinicznej. Zaproponowano konceptualizację pojęcia placebo i omówiono główne skutki działania placebo, tj. efekt placebo i efekt nocebo. Oceniono skuteczność placebo w badaniach nad bólem i w praktyce klinicznej. Zaprezentowano najważniejsze metody wywoływania działania placebo, tj. warunkowanie klasyczne, sugestie słowne i uczenie się przez obserwację. Dyskusji poddano psychologiczne mechanizmy działania placebo, tj. oczekiwania i warunkowanie klasyczne, a także czynniki emocjonalne, które wpływają na działanie placebo, tj. lęk, strach i stres. Artykuł kończą rozważania etyczne nad wykorzystywaniem placebo w badaniach i praktyce klinicznej. Artykuł został przygotowany w ramach realizacji projektu badawczego nr 2014/14/E/HS6/00415 finansowanego przez Narodowe Centrum Nauki.Placebo effects have been extensively investigated in recent years and a number of conceptual frameworks have been developed to capture their mechanisms. The aim of the article is to summarize and critically discuss the current state of the art of placebo effects in pain research and clinical practice. Conceptualization of a placebo is proposed and main placebo effects, i.e., placebo effect and nocebo effect, are described. The effectiveness of the placebo in pain research and clinical practice is evaluated. Main methods of the induction of placebo effects are presented, i.e., classical conditioning, verbal suggestions and observational learning. Psychological mechanisms of placebo effects are discussed, including expectancy and classical conditioning, as well as emotional factors contributing to the placebo effects, i.e., anxiety, fear and stress. Last but not least, ethical issues in the placebo use in research and clinical practice are considered. The article is part of a research project no. 2014/14/E/HS6/00415 funded by the National Science Centre, Poland

Explainable Artificial Intelligence (XAI) in Pain Research: Understanding the Role of Electrodermal Activity for Automated Pain Recognition

Artificial intelligence and especially deep learning methods have achieved outstanding results for various applications in the past few years. Pain recognition is one of them, as various models have been proposed to replace the previous gold standard with an automated and objective assessment. While the accuracy of such models could be increased incrementally, the understandability and transparency of these systems have not been the main focus of the research community thus far. Thus, in this work, several outcomes and insights of explainable artificial intelligence applied to the electrodermal activity sensor data of the PainMonit and BioVid Heat Pain Database are presented. For this purpose, the importance of hand-crafted features is evaluated using recursive feature elimination based on impurity scores in Random Forest (RF) models. Additionally, Gradient-weighted class activation mapping is applied to highlight the most impactful features learned by deep learning models. Our studies highlight the following insights: (1) Very simple hand-crafted features can yield comparative performances to deep learning models for pain recognition, especially when properly selected with recursive feature elimination. Thus, the use of complex neural networks should be questioned in pain recognition, especially considering their computational costs; and (2) both traditional feature engineering and deep feature learning approaches rely on simple characteristics of the input time-series data to make their decision in the context of automated pain recognition

Learning pain from others : a systematic review and meta-analysis of studies on placebo hypoalgesia and nocebo hyperalgesia induced by observational learning

Observing someone experience pain relief or exacerbation after an intervention may induce placebo hypoalgesia or nocebo hyperalgesia. Understanding the factors that contribute to these effects could help in the development of strategies for optimizing treatment of chronic pain conditions. We systematically reviewed and meta-analyzed the literature on placebo hypoalgesia and nocebo hyperalgesia induced by observational learning (OL). A systematic literature search was conducted in the databases PubMed, PsycINFO, Web of Science, ScienceDirect, PsycARTICLES, Scopus, and Academic Search Ultimate. Twenty-one studies were included in the systematic review, 17 of which were suitable for meta-analysis (18 experiments; n = 764 healthy individuals). The primary end point was the standardized mean difference (SMD) for pain following placebo cues associated during OL with low vs high pain. Observational learning had a small-to-medium effect on pain ratings (SMD 0.44; 95% confidence interval [CI] 0.21-0.68; P < 0.01) and a large effect on pain expectancy (SMD 1.11; 95% CI 0.49-2.04; P < 0.01). The type of observation (in-person vs videotaped) modulated the magnitude of placebo hypoalgesia/nocebo hyperalgesia (P < 0.01), whereas placebo type did not (P = 0.23). Finally, OL was more effective when observers' empathic concern (but no other empathy-related factors) was higher (r = 0.14; 95% CI 0.01-0.27; P = 0.03). Overall, the meta-analysis demonstrates that OL can shape placebo hypoalgesia and nocebo hyperalgesia. More research is needed to identify predictors of these effects and to study them in clinical populations. In the future, OL could be an important tool to help maximize placebo hypoalgesia in clinical settings

Pain memory in children: a systematic review and meta-analysis with a meta-regression

The aim of this systematic review and meta-analysis was to analyze the accuracy of memory of pain and the variables that may influence it in children with acute, experimental, and chronic pain. We conducted a search in electronic databases from inception to February 11, 2022. Twelve observational studies and 3 randomized controlled studies were included in the study. The main outcome measure was the accuracy of the memory of the pain intensity (experienced/recalled). To compare the outcomes reported by the studies, we calculated the standardized mean difference (SMD) over time for the continuous variables. The overall meta-analysis showed a small effect size in favor of an overestimation of experienced pain intensity (SMD = 0.28). Subanalyzing per pain context, there was a small effect size in favor of overestimation in the clinical context (SMD = 0.33), but there was no evidence of any change in the accuracy of memory of pain in the experimental context (SMD = 0.07). The mean age of the participants and the proportion of girls significantly predicted the accuracy of the memory of pain. The period since the experienced pain measurement, the intensity of expected and recalled fear, trait anxiety, and anxiety sensitivity did not significantly predict the accuracy of the memory of pain. Children showed an overestimation in pain memory between the experienced and recalled intensity of acute pain, especially in a clinical context. Furthermore, only gender and age were predictors of the accuracy of pain memory. These results highlight the relevance of pain memory to medical practice and future research.Sin financiación7.4 Q1 JCR 20222.445 Q1 SJR 2022No data IDR 2022UE