How Does Observational Learning Produce Placebo Effects? A Model Integrating Research Findings

Can observational learning reinforce open-label placebo hypoalgesia?

ABSTRACT

Previous research has indicated that an open-label placebo can reduce pain in both healthy participants and patients with chronic pain. Because nondeceptive placebos seem to be an effective and more ethical alternative to deceptive placebos, optimizing this kind of treatment is essential. Observational learning was previously shown to induce the deceptive placebo effect; therefore, this study aimed to verify its effectiveness in fortifying the open-label placebo effect. Healthy volunteers (N = 117) were randomly assigned to 4 groups: open-label placebo with observational learning (OLP + OBL), open-label placebo (OLP), deceptive placebo with observational learning (OBL), or control group. Participants underwent baseline and testing measurements, during which they self-reported pain induced by heat stimulation. Between assessments, placebo cream was openly administered in the OLP and OLP + OBL groups. The OLP + OBL group next watched a model experiencing hypoalgesia after cream application. In the OBL group, participants received placebo cream with no information about its effect, and then they watched the model. The placebo effect was successfully evoked in all experimental groups (OLP + OBL, OLP, and OBL), which confirms the effectiveness of both open-label and deceptive placebo interventions for pain reduction. However, the hypoalgesic effect was of similar magnitude in the OLP and OLP + OBL groups, which indicates that observation did not contribute to the effect. The results showed that reinforcing the open-label placebo by observational learning may be redundant, but more research is needed to confirm these findings.

Flower therapy and perceived stress in primary health care nursing professionals: randomized clinical trial

OBJECTIVE

To analyze the effectiveness of Bach flower therapy compared to placebo in reducing perceived stress levels in primary health care nursing professionals.

METHOD

Pragmatic, parallel randomized clinical trial conducted with 87 primary care nursing professionals with self-identified stress, from October 2021 to June 2022, in the cities of Osasco and São Paulo, Brazil. The intervention group (n=43) received the collective flower formula, and the placebo group (n=44) received only the diluent. Data analysis was performed using the linear mixed model, and effect size was measured by partial Eta squared, significance level 5%.

RESULTS

Data analysis showed a significant reduction in perceived stress levels within groups (p=0.038). However, there was no significant difference between the study groups (p=0.750). Participants in the intervention group reported a greater perception of changes than participants in the placebo group, but without statistical significance (p=0,089).

CONCLUSION

The floral formula was not more effective than the placebo formula in reducing perceived stress. There was a significant stress reduction among nursing professionals in both study groups, although with a small effect size.

Social Learning of Placebo Effects in Pain: A Critical Review of the Literature and a Proposed Revised Model

Relatively recently, in 2009, experimental studies were undertaken to determine the role of social observational learning in forming hypoalgesic, analgesic and hyperalgesic responses to a placebo. The research findings obtained in studies published before 2018 were integrated and formed the basis of the theoretical model of social learning of placebo effects in pain proposed by Bajcar and Bąbel. This model considered the involvement of different types of modeling (ie, behavioral modeling, symbolic modeling, and verbal modeling) in shaping placebo hypoalgesia/analgesia and nocebo hyperalgesia. The model assumed that pain expectancies might be involved in observationally induced placebo effects in pain and that the effectiveness of observational learning in shaping placebo effects could be moderated by the observer's dispositions, especially empathy. Based on the latest research data, we propose a modified and significantly extended version of this model. The revised model includes the involvement of particular types of modeling in placebo effects and their role in shaping conscious pain-related expectancies. It explains the role of dispositional empathy in shaping observationally induced placebo effects. Notably, the extended version of the model considers the contribution of the characteristics of the observed person to the magnitude of placebo effects induced by social learning. PERSPECTIVE: The paper proposes a comprehensive theoretical approach to explaining the role of observational learning in shaping placebo effects in pain. The proposed model emphasizes the potential of this form of learning in shaping placebo responses and indicates factors that can modify the effectiveness of observational learning.

Neuropsychological mechanisms of observational learning in human placebo effects

Scientific evidence indicates that placebo effects are psychoneurobiological events involving the contribution of distinct central nervous systems and peripheral physiological mechanisms that influence pain perception and other symptoms. Placebo effects can occur without formal conditioning and direct prior experience because crucial information can be acquired through observational learning. Observation of benefits in another person results in placebo effects of a magnitude like those induced by directly experiencing an analgesic benefit. Understanding the psychological mechanisms of observationally induced placebo effects is a complex and multifaceted endeavor. While previous reviews have highlighted various frameworks and models to understand these phenomena, the underlying biological mechanisms have been overlooked. We summarize critically current understanding of its behavioral and neural mechanisms. Understanding the neural mechanisms of hypoalgesia driven by observation can serve as a foundation for future development of novel theoretical and methodological approaches and ultimately, applications.

Pain Rating is Worth a Thousand Words: Nocebo Hyperalgesia Induced by Verbal Modeling Prevails Over the Effects of Symbolic Modeling and Verbal Suggestion

This study compares the effectiveness of verbal modeling, symbolic modeling, and verbal suggestion in inducing nocebo hyperalgesia. It is the first study to examine the contribution of stress to observationally induced nocebo hyperalgesia. This study's experimental groups represented various sources of social information: a group of people participating in the study (verbal modeling), a single participant (symbolic modeling), and an experimenter (verbal suggestion). During the experiment, participants received electrocutaneous stimuli at the same intensity, some of which were applied with a nocebo (sham device). Participants in the verbal modeling group were acquainted with pain ratings that had allegedly been provided by other participants. The ratings suggested that other participants experienced more pain in the nocebo trials than in the control trials. In the symbolic modeling group, participants observed a videotaped model experiencing more pain in the nocebo than in the control trials. In the verbal suggestion group, participants received a verbal suggestion of hyperalgesia in the nocebo trials and no suggestion in the control trials. No manipulations were used in the control group. To investigate whether nocebo hyperalgesia is stable over time, an additional extinction phase was conducted. Nocebo hyperalgesia was induced by verbal modeling only and was partially mediated by expectancy. Stress was a significant moderator of the induced effect. Nocebo hyperalgesia was extinguished during the extinction phase. The obtained results provide potential implications for minimizing nocebo hyperalgesia in clinical practice by, for instance, controlling patients' expectancies and stress levels. PERSPECTIVE: The study shows the role of pain-related information derived from other people in shaping negative treatment experiences in the individual. Because information from others has a particular impact on individuals experiencing stress, both this information and the stress level of patients should be monitored in the treatment process.

Learning by observing: a systematic exploration of modulatory factors and the impact of observationally induced placebo and nocebo effects on treatment outcomes

Introduction

Observational learning (OL) refers to learning through observing other people's behavior. OL has been suggested as an effective and simple tool to evoke treatment expectations and corresponding placebo and nocebo effects. However, the exact mechanisms by which OL shapes treatment outcomes, its moderating factors and possible areas of application remain unclear. We thus reviewed the existing literature with two different literature searches to answer the following questions: Which influencing factors contribute to OL-induced placebo and nocebo effects (in healthy volunteers and patients) and how large are these effects (search 1)? In which medical fields has OL been used so far to modulate treatment expectancy and treatment outcomes in patients, their caregivers, and at-risk groups (search 2)? We also aimed to explore whether and how the assessment of treatment expectations has been incorporated.

Methods

We conducted two independent and comprehensive systematic literature searches, both carried out on September 20, 2022.

Results

We identified 21 studies that investigated OL-mediated placebo and nocebo effects for pain and itch, the (placebo) efficacy of sham treatment on anxiety, and the (nocebo) induction of medication side effects (search 1). Studies showed that OL can efficiently induce placebo and nocebo effects across different presentation modes, with medium effect sizes on average: placebo effects, d = 0.79 (range: d = -0.36-1.58), nocebo effects, d = 0.61 (range: d = 0.04-1.5). Although several moderating factors have been investigated, their contribution to OL-induced effects remains unclear because of inconsistent results. Treatment expectation was assessed in only four studies. Regarding medical applications of OL (search 2), we found 12 studies. They showed that OL was effectively applied in preventive, therapeutic and rehabilitative interventions and that it was mainly used in the field of psychosomatics.

Discussion

OL effects on treatment outcomes can be both positive and negative. Future research should investigate which individuals would benefit most from OL and how OL can be implemented most effectively to induce placebo and avoid nocebo effects in clinical settings.

Systematic review registration

This work was preregistered at the Center for Open Science as open-ended registration (doi: 10.17605/OSF.IO/FVHKE). The protocol can be found here: https://archive.org/details/osf-registrations-fvhke-v1.

Placebo Hypoalgesia and Nocebo Hyperalgesia Induced by Observational Learning May Be Difficult to Disentangle in a Laboratory Setting

Observational learning (OBL) (seeing pain/pain treatment in others) can evoke placebo hypoalgesia and nocebo hyperalgesia. Data that compare these effects and illuminates the role of expectations and empathy are scarce. Healthy participants (n = 105) were randomized to: 1) placebo OBL, 2) nocebo OBL, or 3) no-observation control group. OBL consisted of a model simulating pain relief or increase after a sham ointment was applied to one arm. Pain was evoked with thermal stimuli on both arms (ointment, contralateral) at baseline and postobservation. Expectations, pain ratings, and physiological data (eg, skin conductance level) were collected. A 3 × 2 × 2 (Group × Arm × Phase) mixed analyses of variance revealed a 3-way interaction that confirmed that OBL modulates pain: F(2, 93) = 6.08, P = .003, ηp2 = .12. Significant baseline-to-post-observation pain increases were shown in the nocebo OBL group, with a bigger increase for the arm with ointment (both P ≤ .007). In the placebo OBL group, pain was higher for the contralateral relative to the ointment arm (P < .001). Baseline-to-post-observation pain increase was significant for the contralateral arm (P < .001). Expectation mediated these effects. Skin conductance level decreased over time during ointment trials in the nocebo OBL group, suggesting reduced physiological arousal. The findings illustrate that OBL modulates pain through expectations. In the placebo OBL group, the pain did not decrease for the ointment but increased for the contralateral stimuli, which may reflect nocebo learning. Experimental OBL paradigms typically examine relative differences between ointment and contralateral cues. This can complicate disentangling placebo hypoalgesia and nocebo hyperalgesia in laboratory settings. Implications for existing theories are discussed. PERSPECTIVE: Data that systematically compare placebo hypoalgesia and nocebo hyperalgesia induced by OBL are scarce. The current work illustrates that these effects may be more difficult to disentangle than previously assumed, which could have implications for existing theories on OBL and placebo effects and their translation to clinical practice.

The Optimal Learning Cocktail for Placebo Analgesia: A Randomized Controlled Trial Comparing Individual and Combined Techniques

This study investigated for the first time the effects of individual and combined application of 3 learning techniques (verbal suggestions, classical conditioning, and observational learning) on placebo analgesia and extinction. Healthy participants (N = 206) were assigned to 8 different groups in which they were taught through either a verbal suggestion, a conditioning paradigm, a video observing someone, or any combination thereof that a placebo device (inactive transcutaneous electric nerve stimulation [TENS]) was capable of alleviating heat pain, whereas one group did not (control). Placebo analgesia was quantified as the within-group difference in experienced pain when the placebo device was (sham) 'activated' or 'inactivated' during equal pain stimuli, and compared between groups. Placebo analgesia was induced in groups with 2 or 3 learning techniques. Significantly stronger placebo analgesia was induced in the combination of all 3 learning techniques as compared to the individual learning techniques or control condition, underlining the additional contribution of 3 combined techniques. Extinction did not differ between groups. Furthermore, pain expectancies, but not state anxiety or trust, mediated placebo analgesia. Our findings emphasize the added value of combining 3 learning techniques to optimally shape expectancies that lead to placebo analgesia, which can be used in experimental and clinical settings. PERSPECTIVE: This unique experimental study compared the individual versus combined effects of 3 important ways of learning (verbal suggestions, classical conditioning, and observational learning) on expectation-based pain relief. The findings indicate that placebo effects occurring in clinical practice could be optimally strengthened if healthcare providers apply these techniques in combination.

Placebo hypoalgesia induced by operant conditioning: a comparative study on the effects of verbal, token-based, and social rewards and punishers

Operant conditioning was shown to be a mechanism of placebo hypoalgesia; however, only verbal rewards and punishers were applied in the previous study. We aimed to induce placebo hypoalgesia using more clinically relevant consequences: token-based and social. Participants were divided into three experimental groups (with verbal, social, and token-based rewards and punishers); and two control groups (with and without placebo application). During operant conditioning, participants in the experimental groups received thermal stimuli of equal intensity and were rewarded for reporting lower pain and punished for reporting higher pain compared to their pretest pain levels. The control groups did not receive any consequences. Our results revealed placebo hypoalgesia was induced by operant conditioning only in the experimental groups with social and token-based reinforcement, compared to the control groups. The hypoalgesic effect found in the group that received verbal reinforcement did not differ significantly from the control group with the placebo application. Moreover, expectations about upcoming pain intensity were found to be a mediator, and the number of reinforcers received during conditioning was a predictor of placebo hypoalgesia. These findings highlight the potential benefits of incorporating token-based and social consequences for optimizing treatment outcomes in pain management.

Socially Acquired Nocebo Effects Generalize but Are Not Attenuated by Choice

BACKGROUND

Socially observing a negative treatment-related experience has been shown to modulate our own experience with the same intervention, leading to worsened health outcomes. However, whether this social learning generalizes to similar but distinct interventions has not been explored nor what manipulations can reduce these effects.

PURPOSE

To determine whether socially acquired nocebo effects can be generated by observing a negative experience with a similar, but distinct intervention, and whether choice can reduce these effects.

METHODS

Across three experiments, a community sample of healthy adults (N = 336) either watched a confederate report cybersickness to the same Virtual Reality (VR) activity they were assigned to (Social Modeling: Consistent); a similar, but different VR activity (Social Modeling: Inconsistent); or did not view the confederate (No Social Modeling). Participants were either given choice over the VR (Choice) or assigned by the experimenter (No Choice).

RESULTS

Across the experiments, there was significantly greater cybersickness in both Social Modeling groups relative to No Social Modeling, while the two Social Modeling groups did not differ. There was no significant effect of Choice or a Choice by Social Modeling interaction. Social Modeling elicited greater anxiety and expectancies for cybersickness. Furthermore, these mechanisms mediated the association between social modeling and cybersickness.

CONCLUSIONS

Socially acquired side-effects were demonstrated to generalize to similar, but distinct interventions, highlighting the diffuse and robust effect social modeling can have on our experiences. However, choice did not attenuate the experience of cybersickness, highlighting the need for alternative methods to counteract the effect of social modeling.

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

ABSTRACT

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.

The development of the Therapeutic Group Context Questionnaire: Reliability and validity measures based on telehealth Group-based Pain Management Programs

INTRODUCTION

In 2016, the Centers for Disease Control and Prevention analyzed the National Health Interview Survey data and found that the occurrence of chronic pain and high-impact chronic pain in the USA was 20.4% and 8%, respectively. Group-based Pain Management Programs have been viewed as significant treatments aiding patients with self-management of chronic pain. The onset of coronavirus disease 2019 (COVID-19) at the beginning of 2020, widely eliminated the in-person Group-based Pain Management Programs. The exploration of therapeutic contextual factors such as the therapeutic alliance and group dynamics in telehealth Group-based Pain Management Programs appears warranted for which reason the Therapeutic Group Context Questionnaire was developed.

METHODS

The therapeutic alliance and group dynamics items in the Therapeutic Group Context Questionnaire were developed from an extensive literature review and underwent examination of content validity, internal consistency, reliability, and validity through telehealth Group-based Pain Management Programs.

RESULTS

Content validity of the Therapeutic Group Context Questionnaire was established in five separate stages and the psychometrics of the Therapeutic Group Context Questionnaire was found to be very good with high internal consistency and reliability (r = 0.85-0.97) and the ability of the Therapeutic Group Context Questionnaire to differentiate between high and low scorers on the SF-36 emotional well-being measure.

DISCUSSION

The examination of therapeutic contextual factors via telehealth Group-based Pain Management Programs using the Therapeutic Group Context Questionnaire appears possible in view of the very good psychometric properties described above. Investigation of therapeutic contextual factors through the Therapeutic Group Context Questionnaire may provide greater insight into the role that these factors may have in telehealth programs and their impact on pain outcomes. Future investigation of the Therapeutic Group Context Questionnaire in non-telehealth Group-based Pain Management Programs, as well as, other disorders being addressed via telehealth appears warranted.

The Biology of Placebo and Nocebo Effects on Experimental and Chronic Pain: State of the Art

(1) Background: In recent years, placebo and nocebo effects have been extensively documented in different medical conditions, including pain. The scientific literature has provided strong evidence of how the psychosocial context accompanying the treatment administration can influence the therapeutic outcome positively (placebo effects) or negatively (nocebo effects). (2) Methods: This state-of-the-art paper aims to provide an updated overview of placebo and nocebo effects on pain. (3) Results: The most common study designs, the psychological mechanisms, and neurobiological/genetic determinants of these phenomena are discussed, focusing on the differences between positive and negative context effects on pain in experimental settings on healthy volunteers and in clinical settings on chronic pain patients. Finally, the last section describes the implications for clinical and research practice to maximize the medical and scientific routine and correctly interpret the results of research studies on placebo and nocebo effects. (4) Conclusions: While studies on healthy participants seem consistent and provide a clear picture of how the brain reacts to the context, there are no unique results of the occurrence and magnitude of placebo and nocebo effects in chronic pain patients, mainly due to the heterogeneity of pain. This opens up the need for future studies on the topic.

Placebo effects on cutaneous pain and itch: a systematic review and meta-analysis of experimental results and methodology

ABSTRACT

Placebo effects, positive treatment outcomes that go beyond treatment processes, can alter sensations through learning mechanisms. Understanding how methodological factors contribute to the magnitude of placebo effects will help define the mechanisms by which these effects occur. We conducted a systematic review and meta-analysis of experimental placebo studies in cutaneous pain and itch in healthy samples, focused on how differences in methodology contribute to the resulting placebo effect magnitude. We conducted meta-analyses by learning mechanism and sensation, namely, for classical conditioning with verbal suggestion, verbal suggestion alone, and observational learning, separately for pain and itch. We conducted subgroup analyses and meta-regression on the type of sensory stimuli, placebo treatment, number of acquisition and evocation trials, differences in calibrated intensities for placebo and control stimuli during acquisition, age, and sex. We replicated findings showing that a combination of classical conditioning with verbal suggestion induced larger placebo effects on pain ( k = 68, g = 0 . 59) than verbal suggestion alone ( k = 39, g = 0.38) and found a smaller effect for itch with verbal suggestion alone ( k = 7, g = 0.14). Using sham electrodes as placebo treatments corresponded with larger placebo effects on pain than when topical gels were used. Other methodological and demographic factors did not significantly affect placebo magnitudes. Placebo effects on pain and itch reliably occur in experimental settings with varied methods, and conditioning with verbal suggestion produced the strongest effects. Although methods may shape the placebo effect to some extent, these effects appear robust overall, and their underlying learning mechanisms may be harnessed for applications outside the laboratory.

The Effect of Observing High or Low Pain on the Development of Central Sensitization

It is unknown whether watching other people in high pain increases mechanical hypersensitivity induced by pain. We applied high-frequency electrical stimulation (HFS) on the skin of healthy volunteers to induce pinprick mechanical hypersensitivity. Before HFS participants were randomly allocated to 2 groups: in the low pain group, which was the control condition, they watched a model expressing and reporting lower pain scores, in the high pain group the model expressed and reported higher scores. The 2 videos were selected on the basis of a pilot/observational study that had been conducted before. We tested the differences in perceived intensity of the HFS procedure, in the development of hypersensitivity and the role of fear and empathy. The high pain group reported on average higher pain ratings during HFS. The perceived intensity of hypersensitivity, but not the unpleasantness or the length of the area was higher in the high pain group. Our results suggest that watching a person expressing more pain during HFS increases one's own pain ratings during HFS and may weakly facilitate the development of secondary mechanical hypersensitivity, although this latter result needs replication. PERSPECTIVE: Observing a person in high pain can influence the perceived pain intensity of a procedure leading to secondary mechanical hypersensitivity, and has a weak effect on hypersensitivity itself. The role of fear remains to be elucidated.

Narcissism in the context of stress: the influence of learned information on attitudes and stress outcomes

Previous research indicates narcissism can aid stress management. Nonetheless, its common perception and dissemination as socially aversive may hamper its acknowledgment and use as an asset in the context of stress. This experimental study investigated the effects of receiving positive or negative information (i.e., prompts) about narcissism in the context of stress on attitudes towards this trait’s association with stress. It also assessed individuals’ experiences of narcissism’s stress-coping properties when one believes themselves to be a high narcissism scorer, via an online survey. Hundred and five adults ($${M}_{age}$$ M age = 32.0; 22–64 years) completed measures of state-stress, music preferences, and narcissism. They were then randomly assigned to either the positive or negative prompt groups, being shown information highlighting the positive or negative impact of narcissism on stress management, respectively. Participants were then informed they scored above average on narcissism, despite their actual questionnaire scores, and undertook a stress-inducing procedure. Self-reported stress, implicit and explicit attitudes were measured pre- and post-prompt presentation. Results showed that, while prompts did not influence attitudes nor stress outcomes, individuals displayed neutral implicit attitudes towards narcissism’s association with stress across measurement timepoints. These findings suggest that people’s attitudes towards narcissism in the context of stress have not been deteriorated by this trait’s predominant negative depiction outside this context. Therefore, the dissemination and establishment of narcissism as an asset for stress-coping may be received by the general population with less resistance than anticipated.

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. Furthermore, 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 effects of cannabidiol and analgesic expectancies on experimental pain reactivity in healthy adults: A balanced placebo design trial

Despite its frequent use for pain relief, no experimental pain research has tested the analgesic effects of cannabidiol (CBD) in humans. The goal of this study was to experimentally test the effects of CBD and expectancies for receiving CBD on human pain reactivity. Using a crossover, 2 × 2 factorial balanced placebo design, drug administration (given inactive substance or given active CBD) and verbal instruction sets (told inactive substance or told active CBD) were experimentally manipulated. Fifteen healthy adults each completed four separate experimental sessions. Participants were randomly assigned to different counterbalanced manipulation conditions at each session: control (told inactive-given inactive); expectancy (told active CBD-given inactive); drug (told inactive-given active CBD); and expectancy + drug (told active CBD-given active CBD). Primary outcomes were pain threshold, tolerance, intensity, unpleasantness, conditioned pain modulation (CPM), and offset analgesia (OA). There was a significant main effect of instructions on OA, such that the OA response was significantly larger when participants were told that they received CBD, regardless of drug content. Pain unpleasantness was significantly reduced in the drug, expectancy, and expectancy + drug conditions, relative to the control condition. The drug and expectancy conditions separately improved CPM, whereas the expectancy + drug and control conditions produced the lowest CPM change scores. We did not detect significant effects for pain threshold, tolerance, or intensity. Our results indicated that separate pain outcomes can be differentially affected by CBD and/or expectancies for receiving CBD. Future investigations of the psychological and pharmacological mechanisms underlying CBD analgesia are warranted. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Validating a biosignature-predicting placebo pill response in chronic pain in the settings of a randomized controlled trial

ABSTRACT

The objective of this study is to validate a placebo pill response predictive model-a biosignature-that classifies chronic pain patients into placebo responders (predicted-PTxResp) and nonresponders (predicted-PTxNonR) and test whether it can dissociate placebo and active treatment responses. The model, based on psychological and brain functional connectivity, was derived in our previous study and blindly applied to current trial participants. Ninety-four chronic low back pain (CLBP) patients were classified into predicted-PTxResp or predicted-PTxNonR and randomized into no treatment, placebo treatment, or naproxen treatment. To monitor analgesia, back pain intensity was collected twice a day: 3 weeks baseline, 6 weeks of treatment, and 3 weeks of washout. Eighty-nine CLBP patients were included in the intent-to-treat analyses and 77 CLBP patients in the per-protocol analyses. Both analyses showed similar results. At the group level, the predictive model performed remarkably well, dissociating the separate effect sizes of pure placebo response and pure active treatment response and demonstrating that these effects interacted additively. Pain relief was about 15% stronger in the predicted-PTxResp compared with the predicted-PTxNonR receiving either placebo or naproxen, and the predicted-PTxNonR successfully isolated the active drug effect. At a single subject level, the biosignature better predicted placebo nonresponders, with poor accuracy. One component of the biosignature (dorsolateral prefrontal cortex-precentral gyrus functional connectivity) could be generalized across 3 placebo studies and in 2 different cohorts-CLBP and osteoarthritis pain patients. This study shows that a biosignature can predict placebo response at a group level in the setting of a randomized controlled trial.

[Seeing others is believing-analgesic placebo effects through observational learning?]

Hintergrund

Es gibt viele Studien zur Placeboanalgesie und deren zugrundliegenden Wirkmechanismen, die eine Behandlung von Patient:innen mit chronischen Schmerzen signifikant verbessern können. Beobachtungslernen als ein Wirkmechanismus wurde hingegen noch wenig untersucht.

Fragestellung

Das Ziel der Arbeit ist es, einen Überblick über die aktuelle Forschungslage zu Placeboanalgesie durch Beobachtungslernen zu geben. Dabei soll geklärt werden, ob Beobachtungslernen überhaupt einen signifikanten Placeboeffekt auslösen kann und durch welche Faktoren dieses Lernen beeinflusst wird.

Material und Methoden

Dafür wurden die Forschungsdatenbanken nach Studien zur Placeboanalgesie durch Beobachtungslernen durchsucht.

Ergebnisse

Nach der Anwendung der Ein- und Ausschlusskriterien verblieben 12 Studien. Es gab nur eine Studie, die an Patient:innen mit chronischen Schmerzen durchgeführt wurde. Die geringe Anzahl an Studien lässt noch keine allgemeingültigen Aussagen zu, aber es gibt erste Hinweise für die folgenden Aussagen: Beobachtungslernen von Placeboeffekten ist unter Laborbedingungen möglich und eine Aufmerksamkeitslenkung ist wichtig. Die Effektstärken reichen von klein bis groß. Die Effekte von klassischer Konditionierung und Beobachtungslernen sind vergleichbar. Live-Modelle, Videoaufnahmen und Bilder lösen ähnliche Effekte aus. Beobachtungslernen führt zu einer Erwartungsänderung.

Diskussion

Die vorliegende Evidenz liefert die Grundlage dafür, dass theoretisch und auch praktisch klinisch signifikante Effekte möglich sind. Weitere Studien sind nötig, um diese Aussagen verlässlich auch auf chronische Schmerzpatient:innen zu beziehen.

The neglect of sex: A call to action for including sex as a biological variable in placebo and nocebo research

Sex differences exist in the prevalence, progression and treatment efficacy of a wide array of medical conditions. While the placebo and nocebo effects have become increasingly relevant in the clinical arena, little is known about the influence of biological sex on placebo and nocebo effects. This paper discusses the existing, relatively limited and sometimes conflicting evidence about how sex impacts the occurrence and magnitude of the placebo and nocebo effects, mainly focusing on pain studies. We present recent evidence that when compared to men, women suffering from chronic orofacial pain may derive greater benefit from the placebo effect for analgesia. Nonetheless, we broadly argue that the field is not currently positioned to draw definitive conclusions and propose several important factors that may explain the inconsistency in the literature and that should be taken into account in future research. These include the specific target symptom of the placebo or nocebo manipulation and whether or not the target is related to the medical condition, the placebo or nocebo induction method, the sex of the experimenter or physician, and so forth. Future research should intentionally include sex a biological variable to favor translation of placebo and nocebo mechanisms into clinical applications.

Associations Between Interindividual Differences, Expectations and Placebo and Nocebo Effects in Itch

Introduction: Placebo and nocebo effects are positive and negative health outcomes that can be elicited by the psychosocial context. They can be mediated by expectations, and may emerge in somatic symptoms even when people are aware of these effects. Interindividual differences (e.g., in personality, affective states) could impact placebo and nocebo responding, but findings are inconsistent. Methods: The current work examined expectation as a mediator of the association between verbal placebo and nocebo suggestions (VSs) and histamine-induced itch across three experimental studies. Moreover, we examined whether interindividual differences (e.g., in optimism, neuroticism, behavioral activation system (BAS), body ignorance) modulated: (1) the direct association between VSs and itch (direct moderation), and (2) the indirect, expectation-mediated association between VSs and itch (moderated mediation). Positive VSs were compared to neutral instructions (Study 1; n = 92) or negative VSs (Studies 2+3; n = 203) in an open-label (i.e., explaining placebo and nocebo effects) or closed-label (concealed) context using PROCESS. First, mediation of VSs effects on itch by expectations was tested. Next, moderation by individual traits was explored using conditional process analyses. Results: The effects of VSs on itch were significantly mediated by expectation in Study 1 and in the open-label (but not closed-label) contexts of Studies 2 and 3. Ignorance of bodily signals marginally moderated the direct effects of VSs on itch when closed-label suggestions were given: at low levels of body ignorance, effects of positive and negative VSs were stronger. Moreover, moderated mediation was observed in the open-label groups of Studies 2 and 3: The expectation-mediated effects of VSs on itch were stronger when BAS drive was lower. Conclusion: Overall, the effects of VSs on itch were mediated by expectations in the open-label, but not the closed-label context. Moreover, the current work suggests that placebo and nocebo effects may be moderated by ignorance of bodily signals and the BAS. There was limited evidence that other interindividual differences modulated placebo and nocebo responding in itch.

To Be (Vaccinated) or Not to Be: The Effect of Media Exposure, Institutional Trust, and Incentives on Attitudes toward COVID-19 Vaccination

The COVID-19 vaccine has become a strategic vehicle for reducing the spread of the pandemic. However, the uptake of the vaccine by the public is more complicated than simply making it available. Based on social learning theory, this study examines the role of communication sources and institutional trust as barriers and incentives as motivators of people's attitudes toward vaccination and actual vaccination. Data were collected via an online panel survey among Israelis aged 18-55 and then analyzed using structural equation modeling (SEM). Findings show that social media trust negatively mediates the effect of exposure to information on the vaccine on attitudes toward vaccination. However, mass media trust and institutional trust positively mediate this relationship. Incentives were effective motivators for forming positive attitudes and moderating the effect of institutional trust on attitude toward vaccination. This study facilitates a deeper understanding of health communication theory in pandemics and makes important recommendations for practitioners and policy makers.

The effect of the model's social status on placebo analgesia induced by social observational learning

Background

Placebo analgesia can be induced by social observational learning. The aim of this study was to determine whether this effect can be influenced by the social status of a model.

Methods

Healthy volunteers were randomly assigned to three groups: a group that observed a video featuring a high-status model (introduced as a professor), a group that observed a video featuring a low-status model (introduced as a janitor), and a control group. Participants observed videos showing a model (of high or low status) undergoing the experimental procedure, during which he received pain stimuli. In each group, half of participants watched a video in which the model rated blue stimuli as more painful (6–8 on the numeric rating scale) and orange stimuli as less painful (1–3 on the numeric rating scale), whereas the other half of participants watched a video in which the model rated orange stimuli as more painful and blue stimuli as less painful. Participants in the control group did not watch any video. Then, all participants received 16 electrocutaneous pain stimuli of the same intensity, preceded by either blue or orange colors. The perceived social status of the model and the trait empathy of participants were measured.

Results

Placebo analgesia was induced in both experimental groups, yet no difference in the magnitude of the effect was found. However, we found that the participants’ individual ratings of the model’s social status predicted the magnitude of placebo analgesia.

Conclusion

This is the first study to show that the perception of a model’s social status is related to the magnitude of placebo analgesia induced by observational learning.

What is pain: Are cognitive and social features core components?

Pain is a universal experience, but it has been challenging to adequately define. The revised definition of pain recently published by the International Association for the Study of Pain addressed important shortcomings of the previous version; however, it remains narrow in its focus on sensory and emotional features of pain, failing to capture the substantial roles of cognitive and social core components of the experience and their importance to advances in pain management. This paper reviews evidence and theoretical models for the significant role social and cognitive factors play in pain experience and we argue that without explicit recognition of these core components in the definition, significant nuances are lost at a cost to understanding and clinical management of pain. A focus on sensory and emotional features perpetuates biomedical interventions and research, whereas recognition of cognitive and social features supports a multidimensional model of pain, advances in interdisciplinary care, and the benefits of cognitive behavioral therapy and self‐management interventions. We also explore the six Key Notes that accompany the new definition of pain, discuss their application to the understanding of pain in childhood, and, in doing so, further explore social and cognitive implications. Considerations are also described for assessment and treatment of pain in pediatric populations.

When one suffers less, all suffer less: Individual pain ratings are more effective than group ratings in producing placebo hypoalgesia

Background

Placebo hypoalgesia can be induced by observing a person (model) whose pain relief is the result of the use of an inert substance or procedure. This study examined whether verbal modelling, that is, showing pain ratings provided by other people, is sufficient to induce placebo hypoalgesia.

Methods

Participants from the experimental groups were acquainted with pain ratings (presented on VASs) derived from a single person (groups 1 and 3) or a group of people (groups 2 and 4) that were allegedly subjected to the same painful procedure. The ratings of pain stimuli that were allegedly applied with placebo were lower than the ratings of stimuli applied without placebo. In two of the experimental groups (group 3 and 4), participants also watched a video recording showing individuals who allegedly provided pain ratings; however, they did not observe them undergoing pain stimulation. The control group did not undergo any manipulation. Then, the participants received a series of the same thermal pain stimuli that were applied either with or without placebo and rated their intensity.

Results

Placebo hypoalgesia was induced only in participants presented with pain ratings provided by a single person, regardless of whether this person was previously seen. However, the pain ratings presented to the participants generally decreased individual pain sensations, regardless of whether they came from a group of people or a single person.

Conclusions

Verbal modelling can produce placebo hypoalgesia and reduce pain sensations. It may be effectively used in clinical practice to modify patients' responses to pain treatment.

Significance

This study shows that knowledge about pain ratings provided by another person is sufficient to induce placebo hypoalgesia; thus, neither direct nor indirect observation of a person experiencing pain is necessary to induce this effect. Pain ratings derived from a group of people can decrease pain sensations but they do not produce placebo hypoalgesia.

The Role of the Observers' Perception of a Model's Self-Confidence in Observationally Induced Placebo Analgesia

The aim of this study was to investigate the effect of a model's self-confidence as well as the observer's self-esteem and self-efficacy on observationally acquired placebo analgesia. In addition, we aimed to verify the stability of the placebo effect induced by observational learning. Participants (n = 60) were randomly assigned to one of three groups: a self-confident model, an unself-confident model, and a control group. In the experimental groups, participants watched a videotaped model who rated the intensity of electrocutaneous pain stimuli applied in the placebo condition as lower than those applied in the non-placebo condition. The different levels of self-confidence in these groups were manifested in the body posture and facial expressions of the model as well as in specific behavior that accompanied the assessment of pain. Then, 16 electrocutaneous pain stimuli of the same intensity, preceded by the placebo or non-placebo, were applied to participants. In both experimental groups, in contrast to the control group, participants experienced less pain in the placebo than in the non-placebo condition. Although the magnitude of placebo analgesia did not differ between the experimental groups, multiple regression analysis revealed that the perceived self-confidence of the model, but not the self-efficacy or self-esteem of the observer, was a significant predictor of the placebo effect. Moreover, placebo analgesia induced by observational learning did not extinguish over the course of the experiment. These results support the premise that the observers' perception of a model's self-confidence plays a significant role in placebo effects. PERSPECTIVE: The results of this study open the discussion on the role of model's features in the effectiveness of observational learning in the induction of placebo effects. The study provides the very first suggestion that the perceived self-confidence of the model may be related to the magnitude of the observationally induced placebo analgesia. It suggests that self-confidence of other patients and medical staff might affect individual pain experiences.

Placebo Effects on Stress, but Not on Pain Reports. A Multi-Experiment Study

Background

Contextual factors, such as participant/experimenter sex may moderate the placebo effects. We tested whether the participant and experimenter sex modulated placebo effects on experimentally induced pain and associated stress.

Objective

To investigate if (i) participant sex and (ii) experimenter sex influence placebo analgesia and subjective and physiological stress in two experiments employing a within-subjects and a mixed design, respectively. Placebo effects were investigated in pain reports, stress, and blood pressure.

Methods

Participants received painful stimulations and a placebo cream. In Experiment One (N = 59) participants underwent a placebo condition (PC) and a natural history condition (NHC) in random order. A placebo cream was applied in the PC and then the heat stimulation temperature was surreptitiously lowered. Identical stimulations were administered in the NHC, but with no cream, no information, and no lowered temperature. In Experiment Two, participants (N = 93) were randomly assigned to three groups receiving either a placebo cream with surreptitiously lowered intensity of electric stimuli (Placebo, PG), a placebo cream (Cream-Control, CCG) without changing the stimuli, or lowered intensity, but with no cream (Pain-Control, PCG) in a mixed design. All participants in both experiments received the same stimuli in the post-test as in the pre-test. Four experimenters (two females) in Experiment One, and five experimenters (two females) in Experiment Two conducted the studies.

Results

No placebo effect was seen on pain. However, there were placebo effects on stress, moderated by participant and experimenter sex: in Experiment One males in the PC had lower diastolic blood pressure (DBP) compared to males in the NHC. Participants in the PC had lower DBP compared to the NHC when tested by a female. In Experiment Two, participants expected more cream effectiveness when a female experimenter administered it, and reported lower stress in the PG compared to the PCG when tested by females.

Conclusion

Our findings highlight a distinction between placebo effects on pain and on associated stress. Secondly, female experimenters recorded lower physiological and subjective stress, higher effectiveness expectations, and lower pain from both sexes compared to male experimenters. Possible reasons for the failure to find a pain placebo effect are discussed.

Understanding Contextual Factors Effects and Their Implications for Italian Physiotherapists: Findings from a National Cross-Sectional Study

An online cross-sectional survey was conducted using Google Docs software. The aim was to understand the management of contextual factors and to identify which are most relevant and which clinicians underestimate. A total of 1250 physiotherapists were chosen from the database of the Manual Therapists group mailing list (GTM-IFOMPT MO) from July to August 2020. A total of 699 responses were received that were considered valid (56%). Participants (40.83%) identified contextual factors (CFs) as "any element, even involuntary, with which the patient interacts during treatment". Physiotherapists individually chose the representation of CF with the "therapeutic relationship" (82.9%), followed by "therapeutic setting" (75.8%). This choice differed between participants belonging to different age groups. Participants favor communication strategies (76.93%). More than half (57.88%) pay attention to patient involvement during the course of care; and in response to the patients' doubts about the use of treatments with limited scientific efficacy, they suggest different medical treatments. The patient's previous clinical experience is not considered significant and does not influence the choice of treatment. Subsequently, however, the participants reported that they stimulate the patients' positive expectations of the success of the clinical outcome (45.27%). Knowledge of contextual factors in physiotherapy appears limited and very heterogeneous. Future research could increase the focus on professional development.

One of us or one of them? The effects of the model's and observer's characteristics on placebo analgesia induced by observational learning

Previous studies have proved that observational learning can induce placebo analgesia, but the factors that influence observationally induced placebo analgesia have not yet been extensively examined. The primary goal of this study was to investigate the effect of information about the role that the observed person (model) plays in the experiment on the magnitude of the observationally induced placebo effect. This study also examined the contribution of the observer’s empathy, conformity and fear of pain to the placebo analgesia induced by observational learning. The effects induced in two experimental groups and one control group were compared. Participants in the experimental groups observed a model introduced as either another participant taking part in the study or a coworker of the experimenter. The model rated the intensity of pain induced by electrocutaneous stimuli preceded by color stimuli. One-half of all participants watched a model rating pain stimuli preceded by the color orange as higher than stimuli preceded by the color blue; for the other half, the ratings were the opposite. There was no observation in the control group. Subsequently, all participants received pain stimuli of the same intensity preceded by orange and blue stimuli and rated the intensity of the experienced pain. Placebo analgesia was found in both experimental groups. However, the way the observed model was introduced to participants did not affect the magnitude of placebo analgesia. Thus, the study showed that the role played by the model is not crucial for observationally induced placebo analgesia. The examined observer’s individual characteristics did not predict the magnitude of placebo effect.

A Meta-Analysis of Therapeutic Pain Neuroscience Education, Using Dosage and Treatment Format as Moderator Variables

OBJECTIVES

This meta-analysis aimed to assess the overall effect of therapeutic pain neuroscience education (TPNE) on chronic musculoskeletal pain and to further assess whether such an effect differs by TPNE dosage as well as other treatment format components. Dosage included the number of TPNE sessions provided as well as the amount of time per TPNE session. Structural components included TPNE provided alone as treatment or combined with other pain management modalities, as well as the inclusion of group-based treatment sessions.

METHODS

Electronic databases were utilized to search for randomized controlled trials that included TPNE. The overall effectiveness of TPNE was estimated on 4 pain outcome measures, including kinesiophobia, pain intensity, pain disability, and pain catastrophizing. The differential effectiveness of TPNE was examined using a mixed-methods moderator analysis on various study-level characteristics to identify potential moderators affecting the overall results.

RESULTS

Significant effects of TPNE were found on all the outcome measures. The only moderator that displayed a significant effect was group-based treatment on kinesiophobia (z = -2.23, P < 0.05, 95% confidence interval [CI] -2.70 to -0.20). Between-group analysis revealed that only interventions that included group sessions were found to be statistically significant (z = 2.20, P < 0.05) and displayed a large effect size (d = 0.80, 95% CI 0.09 to 1.50).

DISCUSSION

Therapeutic pain neuroscience education had a statistically significant impact on all the explored pain outcome measures. However, when investigating the treatment dosage and format moderator variables, they appeared to not have a statistically significant effect except for group-based interventions on kinesiophobia levels.

CONCLUSION

This meta-analysis examined the efficacy of TPNE for patients with chronic pain. It assessed various pain outcome measures following intervention. In addition, this research identified that various moderator variables do not have and do have an impact on the treatment modality of TPNE.

Placebo Analgesia, Nocebo Hyperalgesia, and the Cardiovascular System: A Qualitative Systematic Review

Background: Placebo/nocebo effects involve the autonomic nervous system, including cardiac activity, but studies have reported inconsistent findings on how cardiac activity is modulated following a placebo/nocebo effect. However, no systematic review has been conducted to provide a clear picture of cardiac placebo responses. Objective: The main goal of the present study is to review the effects of placebo analgesia and nocebo hyperalgesia on cardiac activity as measured by blood pressure, heart rate, and heart rate variability. Methods: Using several Boolean keyword combinations, the PubMed, EMBASE, PsycINFO, Cochrane Review Library, and ISI Web of Knowledge databases were searched until January 5, 2020, to find studies that analyzed blood pressure, heart rate, or heart rate variability indexes following a placebo analgesic/nocebo hyperalgesic effect. Results: Nineteen studies were found, with some reporting more than one index of cardiac activity; eight studies were on blood pressure, 14 studies on heart rate, and six on heart rate variability. No reliable association between placebo/nocebo effects and blood pressure or heart rate was found. However, placebo effects reduced, and nocebo effects increased low-frequency heart rate variability, and heart rate variability significantly predicted placebo effects in two studies. Conclusion: Placebo/nocebo effects can have reliable effects on heart rate variability, but not on heart rate and blood pressure.

Context matters: the psychoneurobiological determinants of placebo, nocebo and context-related effects in physiotherapy

Background

Placebo and nocebo effects embody psychoneurobiological phenomena where behavioural, neurophysiological, perceptive and cognitive changes occur during the therapeutic encounter in the healthcare context. Placebo effects are produced by a positive healthcare context; while nocebo effects are consequences of negative healthcare context. Historically, placebo, nocebo and context-related effects were considered as confounding elements for clinicians and researchers. In the last two decades this attitude started to change, and the understanding of the value of these effects has increased. Despite the growing interest, the knowledge and the awareness of using the healthcare context to trigger placebo and nocebo effects is currently limited and heterogeneous among physiotherapists, reducing their translational value in the physiotherapy field.

Objectives

To introduce the placebo, nocebo and context-related effects by: (1) presenting their psychological models; (2) describing their neurophysiological mechanisms; (3) underlining their impact for the physiotherapy profession; and (4) tracing lines for future researches.

Conclusion

Several psychological mechanisms are involved in placebo, nocebo and context-related effects; including expectation, learning processes (classical conditioning and observational learning), reinforced expectations, mindset and personality traits. The neurophysiological mechanisms mainly include the endogenous opioid, the endocannabinoid and the dopaminergic systems. Neuroimaging studies have identified different brain regions involved such as the dorsolateral prefrontal cortex, the rostral anterior cingulate cortex, the periaqueductal gray and the dorsal horn of spine. From a clinical perspective, the manipulation of the healthcare context with the best evidence-based therapy represents an opportunity to trigger placebo effects and to avoid nocebo effects respecting the ethical code of conduct. From a managerial perspective, stakeholders, organizations and governments should encourage the assessment of the healthcare context aimed to improve the quality of physiotherapy services. From an educational perspective, placebo and nocebo effects are professional topics that should be integrated in the university program of health and medical professions. From a research perspective, the control of placebo, nocebo and context-related effects offers to the scientific community the chance to better measure the impact of physiotherapy on different outcomes and in different conditions through primary studies.

Operant conditioning as a new mechanism of placebo effects

BACKGROUND AND OBJECTIVE

Placebo effects are considered to be learning phenomena. There is a growing body of evidence supporting the role of both classical conditioning and observational learning in the induction of placebo effects. However, the third basic learning process, operant conditioning, was not considered as a mechanism of placebo effects until very recently. Unlike classically conditioned responses, which are induced by stimuli that precede the behaviour, operant behaviours are shaped and maintained by their consequences. Thus, placebo effects may not only result from pairing an active intervention with the stimuli that accompany its administration (placebo) but also positive (e.g. the ability to perform a desired activity) or negative reinforcement (e.g. pain relief) of placebo administration may increase the frequency of taking placebos in the future. The paper reviews the evidence supporting the idea of operant conditioning as a mechanism of placebo effects and discusses it in the context of the general principles of operant conditioning, the operant conditioning account of pain modulation and research findings on the role of operant conditioning in pain modulation.

DATABASES AND DATA TREATMENT

This is a narrative review.

RESULTS

Seven lines of research are proposed to study the role of operant conditioning in producing placebo effects.

CONCLUSIONS

Operant conditioning account of placebo effects has practical implications both for routine clinical practice and the placebo arms of randomized controlled trials.

SIGNIFICANCE

The operant conditioning account of placebo effects is discussed from the theoretical perspective of the general principles of operant conditioning and the operant conditioning account of pain modulation. The paper identifies seven lines of research on the role of operant conditioning in producing placebo effects, and highlights the practical implications of the operant conditioning account of placebo effects both for routine clinical practice and the placebo arms of randomized controlled trials.

Rewarded placebo analgesia: A new mechanism of placebo effects based on operant conditioning

BACKGROUND

Placebo analgesia is explained by two learning processes: classical conditioning and observational learning. A third learning process, operant conditioning, has not previously been investigated as a mechanism of placebo effects. We aimed to induce placebo analgesia by operant conditioning.

METHODS

Three groups of participants received electrocutaneous pain stimuli of the same intensity, preceded by either an orange or blue stimulus. In the conditioning phase of the study, participants from the experimental group were rewarded for low pain responses following one of the colour stimuli (placebo) and for high pain responses following the other colour stimuli (non-placebo). Moreover, they were punished when their pain responses were high following placebo stimuli and low following non-placebo stimuli. To investigate the role of contingency, that is dependent relation between rewards/punishers and pain responses, the random-control group received rewards and punishers in a non-contingent manner. The colour-control group did not receive any rewards or punishers to control for nonassociative learning. Pain intensity ratings were used as an outcome measure, and verbal feedback on pain ratings was used as rewards/punishers.

RESULTS

When rewarding and punishment were stopped, only participants from the experimental group experienced less pain following the placebo than following the non-placebo stimuli; that is, placebo analgesia was found in this group. This effect was not extinguished during the study.

CONCLUSIONS

Placebo analgesia can be induced by operant conditioning, which should be considered a third mechanism for producing placebo effects. Moreover, the contingency between pain responses and rewards/punishers is crucial to induce placebo analgesia through operant conditioning.

SIGNIFICANCE

According to the current placebo literature, placebo analgesia can be explained by two learning processes: classical conditioning and observational learning. A third learning process, operant conditioning, has not previously been investigated as a mechanism of placebo effects. Our study reveals that patients can learn placebo analgesia as a result of operant conditioning, suggesting that randomized controlled trials could be improved by controlling the reinforcement that might occur spontaneously when patients interact with, for example, medical personnel.