Nocebo and pain: An overview of the psychoneurobiological mechanisms

Positive Treatment Expectancies Reduce Clinical Pain and Perceived Limitations in Movement Ability Despite Increased Experimental Pain: A Randomized Controlled Trial on Sham Opioid Infusion in Patients with Chronic Back Pain

BACKGROUND

Increasing evidence for the efficacy of analgesic placebo effects in laboratory studies with healthy persons raises the question whether placebos could be used to improve the treatment of pain patients. Expectancies play a central role in shaping analgesic placebo but also nocebo effects.

OBJECTIVES

We investigated to what extent a sham opioid infusion (saline solution) produces sustained clinically relevant placebo and nocebo effects in chronic back pain patients.

METHODS

Fifty-nine patients received the sham opioid infusion applied via a large drain dressing and were compared to 14 control patients without intervention (natural history, NH) while experimental pain stimuli were applied. All subjects were told that the infusion would decrease pain although in rare cases pain increase would be possible (induction of expectancy). In addition, conditioning was introduced where the participants either experienced a decrease in experimental pain (n = 17; placebo conditioning), an increase (n = 21; nocebo conditioning), or no change (n = 21, no conditioning).

RESULTS

Compared to the NH group, all infusion groups showed positive treatment expectancies and significantly (p < 0.001) reduced clinical back pain (primary outcome) and pain-related disability (secondary outcome, assessed by self-reported functional capacity and perceived impairment of mobility). Even the nocebo conditioned group experiencing increased experimental pain developed positive treatment expectancies followed by reduced pain experience. Positive treatment expectancies and relief in clinical back pain were significantly positively correlated (r = 0.72, p < 0.01).

CONCLUSIONS

These findings suggest that it may be beneficial to explicitly shape and integrate treatment expectancies into clinical pain management.

Pain Response to Open Label Placebo in Induced Acute Pain in Healthy Adult Males

Background

Open label placebos with patient education are effective in reducing chronic pain, and recent studies on their effect on pain have established interest in this field. Nevertheless, data on their effect on acute pain are scarce, and on hyperalgesia and allodynia, absent. This study assessed the effect of open label placebos on acute pain in healthy adult males and the influence of placebo education.

Methods

Thirty-two healthy males were included in this prospective, randomized, assessor-blinded crossover, single-center study assessing pain intensities (via numeric rating scale), area of hyperalgesia (von Frey filament), and allodynia (dry cotton swab) in a pain model utilizing intracutaneous electrical stimulation. The authors compared the effect of intravenous open label placebo on pain compared to no treatment. The authors further examined the effect of placebo on hyperalgesia and allodynia, and the influence of education (short vs. detailed) before placebo application. Saliva cortisol concentrations were also measured.

Results

Pain ratings (median, first to third quartile) were 21% lower during placebo treatment compared to no treatment, 4.0 (3.2 to 4.9) versus 5.1 (4.7 to 5.4), respectively (P = 0.001). The areas of hyperalgesia and allodynia were lower during placebo treatment compared to no treatment (hyperalgesia, 30 cm2 [17 to 47] vs. 55 cm2 [42 to 68], P = 0.003; allodynia, 24 cm2 [11 to 39] vs. 45 cm2 [31 to 62], P = 0.007). This corresponds to reductions of 47%. The extent of placebo education had no effect on pain. Saliva cortisol decreased significantly over time and was under the limit of detectability in the majority of participants in postbaseline measurements in both treatment branches. Baseline cortisol was not associated with the placebo effect or strength applied of current to reach defined pain ratings.

Conclusions

Open label placebos might play a role in multimodal analgesic concepts.

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

The Clinical Implications of Nocebo Effects for Biosimilar Therapy

Nocebo effects encompass negative responses to inert interventions in the research setting and negative outcomes with active treatments in the clinical research or practice settings, including new or worsening symptoms and adverse events, stemming from patients' negative expectations and not the pharmacologic action of the treatment itself. Numerous personality, psychosocial, neurobiological, and contextual/environmental factors contribute to the development of nocebo effects, which can impair quality of life and reduce adherence to treatment. Biologics are effective agents widely used in autoimmune disease, but their high cost may limit access for patients. Biosimilar products have gained regulatory approval based on quality, safety, and efficacy comparable to that of originator biologics in rigorous study programs. In this review, we identified gaps in patients' and healthcare professionals' awareness, understanding, and perceptions of biosimilars that may result in negative expectations and nocebo effects, and may diminish their acceptance and clinical benefits. We also examined features of nocebo effects with biosimilar treatment that inform research and clinical practices. Namely, when biosimilars are introduced to patients as possible treatment options, we recommend adoption of nocebo-reducing strategies to avoid negative expectations, including delivery of balanced information on risk-benefit profiles, framing information to focus on positive attributes, and promoting shared decision-making processes along with patient empowerment. Healthcare professionals confident in their knowledge of biosimilars and aware of bias-inducing factors may help reduce the risk of nocebo effects and improve patients' adherence in proposing biosimilars as treatment for autoimmune diseases such as rheumatoid arthritis and inflammatory bowel disease.

Optimizing audiovisual itch induction: the role of attention and expectancy

Linked Article: Marzell et al. Br J Dermatol 2020; 182:1253–1261.

The potential role of illness expectations in the progression of medical diseases

To what extent can one’s mind promote direct changes to the body? Can one’s beliefs about the body become a physical reality, without mediating effects from behaviors? Specifically, can medical symptoms and the course of a disease be directly affected by a person’s mindset about the illness?

There is a vast literature about placebo and nocebo effects, that promote physical changes by creating the expectation of a change through a primer (for example, a fake pill). Placebos, however, often imply deception, or at least ambiguity, to be effective. The concept of Illness Expectation describes the expectations, both implicit and explicit, that a person who has received a diagnosis makes about the course of the disease. It can be characterized by different degrees of rigidity, and it is argued here that these expectations can ultimately lead to changes in the disease progression. These changes may happen through behavior modifications, or through a non-behavioral pathway, which may deserve exploration efforts from the scientific literature.

Reconceptualizing the measurement of expectations to better understand placebo and nocebo effects in psychological responses to exercise

The understanding of placebo and nocebo effects in psychological responses to exercise may be improved by measuring expectations. Despite availability of several validated expectation measures, we argue for using scales that take both positive and negative expectations for exercise-induced changes into account. A cross-sectional survey was used to collect information on positive and negative expectations pertaining to how exercise would affect 14 different outcomes related to psychological health (n = 966). Outcomes for which a majority of the sample (>50%) reported positive expectations for exercise-induced changes included: psychological well-being (75.3%), depression (74.3%), relaxation (74.2%), sleep quality (73.3%), stress (72.2%), anxiety (69.8%), energy (67.1%), and attention (60.2%). Outcomes for which a majority of the sample (>50%) reported a negative expectation for exercise-induced changes were muscle pain (66.3%), fatigue (57.3%), and joint pain (50.7%). Across all 14 outcomes, the percentage of participants with negative expectations for exercise-induced changes ranged from 5.9 to 66.3%. Elucidating the potential presence of placebo and nocebo effects through measurement of expectations may improve the understanding of variability in the direction and magnitude of exercise-related effects on psychological health. Although there were only 3 outcomes for which the majority of participants reported negative expectations, we found that negative expectations were present to some degree for all 14 outcomes. Thus, for researchers who wish to characterize expectations in studies of psychological responses to exercise, we recommend using measures that give equal consideration to positive and negative expectations.

Pain neuroscience education: Which pain neuroscience education metaphor worked best?

BACKGROUND

The use of pain neuroscience education (PNE) has been shown to be effective in reducing pain, improving function and lowering fear and catastrophisation. Pain neuroscience education utilises various stories and metaphors to help patients reconceptualise their pain experience. To date no individualised study has looked at which stories and metaphors may be the most effective in achieving the positive outcomes found with the use of PNE.

OBJECTIVES

This study examined patient responses to the usefulness of the various stories and metaphors used during PNE for patients who underwent surgery for lumbar radiculopathy.

METHOD

Twenty-seven participants who received preoperative PNE from a previous randomised control trial (RCT) were surveyed 1-year post-education utilising a 5-point Likert scale (0 - 'do not remember', 4 - 'very helpful') on the usefulness of the various stories and metaphors used during the PNE session. Participant demographics and outcomes data (pain intensity, function and pain knowledge) were utilised from the previous RCT for analysis and correlations.

RESULTS

Nineteen surveys were returned for a response rate of 70%. No story or metaphor mean was below 2 - 'neutral', lowest mean at 2.53; 6 of the 11 stories or metaphors scored a mean above 3 - 'helpful'.

CONCLUSION

No individual story or metaphor stood out as being predominately important in being helpful in the recovery process through the use of PNE.

CLINICAL IMPLICATIONS

The overall messages of reconceptualising pain during PNE may be more important than any individual story or metaphor.

The Knowledge of Contextual Factors as Triggers of Placebo and Nocebo Effects in Patients With Musculoskeletal Pain: Findings From a National Survey

Backgrounds: Contextual factors (CFs) have been recently proposed as triggers of placebo and nocebo effects in musculoskeletal pain. CFs encompass the features of the clinician (e.g. uniform), patient (e.g. expectations), patient-clinician relationship (e.g. verbal communication), treatment (e.g. overt therapy), and healthcare setting (e.g. design). To date, the researchers' understanding of Italian patients' knowledge about the role of CFs in musculoskeletal pain is lacking. Objectives: The aim of this study was to investigate attitudes and beliefs of Italian patients with musculoskeletal pain about the use of CFs in clinical practice. Methods: A national sample of Italian patients with musculoskeletal pain was recruited from 12 outpatient private clinics in Italy. An invitation to participate in an online survey was sent to patients: a) exhibiting musculoskeletal pain; b) aged 18-75; c) with a valid e-mail account; and d) understanding Italian language. Survey Monkey software was used to deliver the survey. The questionnaire was self-reported and included 17 questions and 2 clinical vignettes on the patients' behavior, beliefs, and attitudes towards the adoption of CFs in clinical practice. Descriptive statistics and frequencies described the actual number of respondents to each question. Results: One thousand one hundred twelve patients participated in the survey. Five hundred seventy-four participants were female (52%). The average age of patients was 41.7 ± 15.2 years. Patients defined CFs as an intervention with an unspecific effect (64.3%), but they believed in their clinical effectiveness. They identified several therapeutic effects of CFs for different health problems. Their use was considered ethically acceptable when it exerts beneficial psychological effects (60.4%), but it was banned if considered deceptive (51.1%). During clinical practice, patients wanted to be informed about the use of CFs (46.0%) that are accepted as an addition to other interventions to optimize clinical responses (39.3%). Moreover, patients explained the power of CFs through body-mind connections (37.1%). Conclusion: Patients with musculoskeletal pain had positive attitudes towards the use and effectiveness of CFs when associated with evidence-based therapy. They mostly perceived the adoption of CFs in clinical practice as ethical.

Boundary effects of expectation in human pain perception

Perception of sensory stimulation is influenced by numerous psychological variables. One example is placebo analgesia, where expecting low pain causes a painful stimulus to feel less painful. Yet, because pain evolved to signal threats to survival, it should be maladaptive for highly-erroneous expectations to yield unrealistic pain experiences. Therefore, we hypothesised that a cue followed by a highly discrepant stimulus intensity, which generates a large prediction error, will have a weaker influence on the perception of that stimulus. To test this hypothesis we collected two independent pain-cueing datasets. The second dataset and the analysis plan were preregistered ( https://osf.io/5r6z7/ ). Regression modelling revealed that reported pain intensities were best explained by a quartic polynomial model of the prediction error. The results indicated that the influence of cues on perceived pain decreased when stimulus intensity was very different from expectations, suggesting that prediction error size has an immediate functional role in pain perception.

It is not just the drugs that matter: the nocebo effect

The role of psychological mechanisms in the treatment process cannot be underestimated, the well-known placebo effect unquestionably being a factor in treatment. However, there is also a dark side to the impact of mental processes on health/illness as exemplified by the nocebo effect. This phenomenon includes the emergence or exacerbation of negative symptoms associated with the therapy, but arising as a result of the patient's expectations, rather than being an actual complication of treatment. The exact biological mechanisms of this process are not known, but cholecystokinergic and dopaminergic systems, changes in the HPA axis, and the endogenous secretion of opioids are thought to be involved. The nocebo effect can affect a significant proportion of people undergoing treatment, including cancer patients, leading in some cases to the cessation of potentially effective therapy, because of adverse effects that are not actually part of the biological effect of treatment. In extreme cases, as a result of suggestions and expectations, a paradoxical effect, biologically opposite to the mechanism of the action of the drug, may occur. In addition, the nocebo effect may significantly interfere with the results of clinical trials, being the cause of a significant proportion of complications reported. Knowledge of the phenomenon is thus necessary in order to facilitate its minimalization and thus improve the quality of life of patients and the effectiveness of treatment.

The impact of contextual factors on nursing outcomes and the role of placebo/nocebo effects: a discussion paper

INTRODUCTION

Placebo and nocebo effects represent one of the most fascinating topics in the health care field.

OBJECTIVES

the aims of this discussion paper were (1) to briefly introduce the placebo and nocebo effects, (2) to elucidate the contextual factors able to trigger placebo and nocebo effects in the nursing field, and (3) to debate the impact of contextual factors on nursing education, practice, organisation, and research.

METHODS

a narrative review was conducted based on the available evidence.

RESULTS

Placebo responses (from Latin "I shall please") are a beneficial outcome(s) triggered by a positive context. The opposite are the nocebo effects (from Latin "I shall harm"), which indicates an undesirable outcome(s) caused by a negative context. Both are complex and distinct psychoneurobiological phenomena in which behavioural and neurophysiological changes arise subsequent to an interaction between the patient and the health care context.

CONCLUSION

Placebo and nocebo concepts have been recently introduced in the nursing discipline, generating a wide debate on ethical issues; however, the impact on nursing education, clinical practice, nursing administration, and research regarding contextual factors triggering nocebo and placebo effects has not been debated to date.

The nocebo effect as a source of bias in the assessment of treatment effects

The term nocebo effect refers to the harmful outcomes that result from people’s negative beliefs, anticipations, or experiences related to the treatment rather than the pharmacological properties of the treatment. These outcomes may include a worsening of symptoms, a lack of expected improvement, or adverse events, and they may occur after the active treatment and the placebo that is supposed to imitate it.  The nocebo effect is always unwanted and may distort estimates of treatment effectiveness and safety; moreover, it may cause discontinuation of therapy or withdrawal from a trial.

The nocebo effect may be unintentionally evoked by the explanations given by healthcare professionals during a clinical consultation or consent procedures, or by information from other patients, the media, or the Internet. Moreover, it may be a consequence of previous bad experiences with the treatment, through learning and conditioning, and the conditioning may happen without patients’ conscious awareness. In trial settings, a study design, for example lack of blinding, may introduce bias from the nocebo effect.

Unlike the placebo effect, which is usually taken into consideration while interpreting treatment outcomes and controlled for in clinical trials, the nocebo effect is under-recognised by clinical researchers and clinicians. This is worrying, because the nocebo phenomenon is common and may have potentially negative consequences for the results of clinical treatment and trials. It is therefore important that doctors and medical researchers consider any potential nocebo effect while assessing the treatment effect and try to minimise it through careful choice and phrasing of treatment-related information given to patients.

The Role Of Effective Radiation Therapist-Patient Communication In Alleviating Treatment-Related Pain And Procedural Discomfort During Radiotherapy

PURPOSE

Managing radiotherapy (RT)-induced pain is essential for reducing the likelihood of treatment interruption and improving the chance of tumor control. The current study aimed to examine the role of radiation therapist (RTTs) interaction and effective information communication in modulating patients' experiences of pain and discomfort during RT.

METHODS

Participants were 91 cancer patients undergoing RT for the first time referred to the Radiotherapy Unit of Sant'Orsola-Malpighi Hospital in Bologna, Italy. Patient-reported outcome measures included patient satisfaction with the quality of the relationship and the information received by the RTTs, assessed by the Communication with RTTs - Shortened, scale, and pain and discomfort experienced during RT, assessed through two VAS scales. Attitudes toward RT were also assessed. All measures were collected as patients were approximately halfway through the overall RT duration (on average at the end of the 12th session).

RESULTS

Patient satisfaction with RTT relationships and treatment-information communication was significantly related to RT-induced pain intensity and patient attitudes toward RT. The more satisfied patients were with RTT interactions and communication, the more positive their attitudes were toward RT and the lower the pain intensity experienced during treatment.

CONCLUSION

Clinical implications can be drawn in terms of highlighting the need for RTTs to be mindful of their technical and supportive role in delivery of patient care and in structuring treatment information content in a way that contrasts potential nocebo effects related to patients' negative expectations about RT. The findings support the idea that RTTs may benefit from training interventions and structured education sessions with a focus on interpersonal skills and patient-centered communication.

The interplay of exercise, placebo and nocebo effects on experimental pain

Over the last few decades, placebo, and nocebo effects in general, have been investigated at rest. This proposed study explores whether they could work even when the experience of pain occurs during a movement. Exercise itself can have a hypoalgesic effect, suggesting that placebo- and exercise-induced hypoalgesia could foster pain reduction. In the present study, we investigated the interplay of exercise, placebo and nocebo effects on pain. To this aim, we developed a machine-controlled isotonic motor task to standardize the exercise across participants and used a well-validated model of placebo and nocebo manipulations with reinforced expectations via a conditioning procedure including visual cues paired with heat painful stimulations. Participants reported expectations and pain on a trial-by-trial basis. We found that the standardized isotonic exercise elicited a reduction of pain intensity. Moreover, both exercise and placebo induced comparable hypoalgesic effects. When the exercise was added, placebo and nocebo effects were influenced by expectations but were not affected by fatigue or sex differences. Exercise-, placebo- and nocebo-induced pain modulation are likely to work through distinct mechanisms and neurophysiological research is needed to fully exploit the implications for sport, rehabilitation and pain management.

The Role of Patient-Practitioner Relationships in Placebo and Nocebo Phenomena

INTRODUCTION

Placebo and nocebo effects form part of all therapeutic environments and play a significant role in the effectiveness of treatment outcomes. Patient expectancies drive these phenomena, which can be shaped through contextual factors including verbal suggestions, conditioning, and social observation.

OBJECTIVES

This review seeks to identify the biopsychosocial factors of the patient-practitioner interaction that play a role in the development of placebo and nocebo effects, as well as the anthropological elements of the biodynamic process of relating that are meaningful in the development of expectancies.

METHODS

We conducted a narrative review of frameworks of the placebo and nocebo effect, including the impact of expectancies and interpersonal relationships in the context of healing and the clinical setting.

RESULTS

Expectancies leading to placebo and nocebo effects can be modified by macro and micro factors, such as culture and society, as well as individual psychobiological traits, respectively. The developmental sociobiological adaptations that form and consolidate mindsets and meaningful contexts play an important role in shaping patient expectancies, as well as patients' conscious and subconscious reactions to signs and actions taking place within the clinical environment. Practitioner characteristics, like empathy, friendliness, and competence, favor the formation of positive expectancies. Caring and warm patient-practitioner interactions can enhance the therapeutic value of clinical encounters when patients' positive expectancies are actively encouraged and engaged.

CONCLUSION

A patient-centered approach rooted in demonstrating care and empathy can positively enhance a patient's experience within the clinical environment and activate psychosociobiological adaptations associated with the placebo phenomenon. Pain patients could particularly benefit from non-invasive approaches for improving treatment effectiveness and quality-of-life.

Optimizing Placebo and Minimizing Nocebo to Reduce Pain, Catastrophizing, and Opioid Use: A Review of the Science and an Evidence-Informed Clinical Toolkit

Pain, a noxious psychosensory experience, motivates escape behavior to assure protection and survival. Psychological factors alter the experience and trajectory of pain, as well as behavior and treatment response. In the context of pain, the placebo effect (expectation for pain relief) releases endogenous opioids and facilitates analgesia from exogenously administered opioids. Nocebo hyperalgesia (expectation for persistent or worsening pain) opposes endogenous opioid analgesia and patient engagement in prescription opioid tapering. Reductions in nocebo hyperalgesia and pain catastrophizing may enhance descending modulation of pain, mediate adaptive structural brain changes and promote patient engagement in opioid tapering. Interventions that minimize nocebo and optimize placebo may adaptively shape the central nervous system toward pain relief and potentially opioid reduction. Here we provide a critical description of catastrophizing and its impact on pain, placebo and nocebo effects. We also consider the importance of minimizing nocebo and optimizing placebo effects during prescription opioid tapering, and offer a clinical toolkit of resources to accomplish these goals clinically.

Placebo Effect: Theory, Mechanisms and Teleological Roots

Why pain can be relieved with placebos is heavily debated. The term "placebo effect," implies that the placebo treatment induces pain relief which is imprecise because it is the mental cueing to the context of treatment and not the placebo itself that can reduce pain. This essay reverts to fundamentals of perception that have been used to explain how context generates predictions that can in turn effect the process of processing, organizing and interpreting of sensory inputs received from the periphery. We reinterpret placebo effect as a neurobiological phenomenon that occurs through the process of reward and aversive learning. The brain uses learnt information to generate predictions. The perceptual processes adjust the experience of pain to fit with the predictions generated from prior information. Placebo effect is thus understandably a result of the expectations and mental states that result from engaging in the process of treatment. These processes have teleological roots in ancient medicine and are the context that produces these responses is transforming with the evolution of modern medicine. Thus, when placebo effect is observed, the potent agent that induces pain reduction is not the placebo itself, but the mental cueing to the context of taking treatment.

Placebo hypoalgesic effects in pain: Potential applications in dental and orofacial pain management

Placebo and nocebo effects are present within every treatment and intervention, and can be purposefully enhanced and reduced, respectively, in order to improve patients' clinical outcomes. A plethora of research has been conducted on the mechanisms of placebo hypoalgesia and nocebo hyperalgesia in experimental and clinical settings. However, its implications in particular clinical settings such as orthodontic pain management remain underexplored. We conducted a search of the literature regarding placebo analgesia, orthodontic pain management, and orofacial and dental pain. Articles were qualitatively assessed and selected based on the scope of this narrative review. Although no studies investigating the extent of the implications of the placebo and nocebo phenomena in the orthodontic clinical setting were found, we herein present a comprehensive review on the influences of placebo and nocebo effects in experimental and clinical pain management, as well as on the potential for engaging placebo-related endogenous pain modulation for orthodontic pain management. Ethical considerations for the clinical application of placebos are discussed, and future research directions are presented.

Nocebo Effects: Neurobiological Mechanisms and Strategies for Prevention and Optimizing Treatment

Psychosocial and contextual factors, such as patient-physician relationship, prior treatment experience, and treatment expectation, can either improve or compromise treatment efficacy. These phenomena are commonly specified as placebo and nocebo effects. As placebo and nocebo effects can influence symptom development, adverse event rate, and treatment efficacy, it is crucial to be aware of these effects and to develop strategies for prevention to optimize treatment outcomes. While experimental studies have made substantial progress in elucidating the psychosocial and neurobiological mechanisms underlying placebo effects, the detailed mechanisms of nocebo effects remain largely unexplored. A better understanding of these mechanisms promises to facilitate the development of easy-to-use strategies in clinical care to improve overall treatment outcomes and patient satisfaction.

Clinical relevance of contextual factors as triggers of placebo and nocebo effects in musculoskeletal pain

Placebo and nocebo effects are embodied psycho-neurobiological responses capable of modulating pain and producing changes at different neurobiological, body at perceptual and cognitive levels. These modifications are triggered by different contextual factors (CFs) presented in the therapeutic encounter between patient and healthcare providers, such as healing rituals and signs. The CFs directly impact on the quality of the therapeutic outcome: a positive context, that is a context characterized by the presence of positive CFs, can reduce pain by producing placebo effects, while a negative context, characterized by the presence of negative CFs, can aggravate pain by creating nocebo effects. Despite the increasing interest about this topic; the detailed study of CFs as triggers of placebo and nocebo effects is still lacked in the management of musculoskeletal pain.

Increasing evidence suggest a relevant role of CFs in musculoskeletal pain management. CFs are a complex sets of internal, external or relational elements encompassing: patient’s expectation, history, baseline characteristics; clinician’s behavior, belief, verbal suggestions and therapeutic touch; positive therapeutic encounter, patient-centered approach and social learning; overt therapy, posology of intervention, modality of treatment administration; marketing features of treatment and health care setting. Different explanatory models such as classical conditioning and expectancy can explain how CFs trigger placebo and nocebo effects. CFs act through specific neural networks and neurotransmitters that were described as mediators of placebo and nocebo effects.

Available findings suggest a relevant clinical role and impact of CFs. They should be integrated in the clinical reasoning to increase the number of treatment solutions, boosts their efficacy and improve the quality of the decision-making. From a clinical perspective, the mindful manipulation of CFs represents a useful opportunity to enrich a well-established therapy in therapeutic setting within the ethical border. From a translational perspective, there is a strong need of research studies on CFs close to routine and real-world clinical practice in order to underline the uncertainty of therapy action and help clinicians to implement knowledge in daily practice.

The Placebo Phenomenon: A Narrow Focus on Psychological Models

The placebo effect is a complex phenomenon that can be described from neurobiological, psychosocial, and epistemological perspectives. Different leaders in the field have proposed multiple theories and models that attempt to describe both the nature and the mechanisms of action underlying placebo effects. This article focuses on the most relevant psychological models that have been suggested for characterizing the different mechanisms underlying the placebo effect. We outline how the dynamic psychoneurobiological aspects of the placebo phenomenon can be a potential reliable and useful tool in daily clinical practice for illness and symptom management within a wide variety of specialties and health-care practices.

The sustained influence of prior experience induced by social observation on placebo and nocebo responses

Background

Social observation is one of the main ways to gain experience. Similar to first-person experience, observational experience affects the effectiveness of subsequent treatments. Yet, it is still undetermined whether the influence of social observation on placebo and nocebo effects to subsequent treatments remains even if related experience occurred a few days ago.

Methods

Eighty-two participants were recruited and each of them was randomly assigned to one of the four experimental groups acquiring first-person or observational experience, which was either effective or ineffective. For the first-person groups, participants were presented with pain cues paired with pain stimuli in person. In the effective condition, low pain cues were paired with low pain stimuli, and high pain cues were paired with high pain stimuli. In contrast, the associations between cues and pain stimuli were not established in the ineffective condition. Similarly, for the observational groups, participants received effective/ineffective treatment through observation. Five or six days later, all participants underwent a conditioning phase followed by a test phase composed of two tests, where participants were asked to report their perceived pain.

Results

Placebo and nocebo responses to subsequent treatments can be affected by prior experience gained several days ago regardless of acquisition ways, and both placebo and nocebo responses in the effective condition were significantly larger than those in the ineffective condition. Furthermore, once placebo and nocebo effects were elicited, the latter was more persistent, while the former was more likely to diminish.

Conclusion

First-person and observational experience obtained a few days ago could affect the following treatments, which advance our understanding of the crucial and sustained influence of social observation on placebo analgesia and nocebo hyperalgesia, and provide insights into clinical applications.