Conscious expectation and unconscious conditioning in analgesic, motor, and hormonal placebo/nocebo responses

Placebo Effects in Traumatic Brain Injury

In recent years, several randomized controlled trials evaluating pharmaceutical treatments for traumatic brain injury (TBI) have failed to demonstrate efficacy over placebo, with both active and placebo arms improving at comparable rates. These findings could be viewed in opposing ways, suggesting on the one hand failure of the tested outcome, but on the other, representing evidence of robust placebo effects in TBI. In this article, we examine several of the primary psychological processes driving placebo effects (verbal suggestion, cognitive re-framing, interpersonal interactions, conditioning, therapeutic alliance, anxiety reduction) as well as placebo neurobiology (top-down cortical regulation, reward system activation, dopaminergic and serotonergic neurotransmission). We then extrapolate from the literature to explore whether something inherent in TBI makes it particularly responsive to placebos. Viewed as such here, placebos may indeed represent a powerful and effective treatment for a variety of post-TBI complaints.

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.

Effects of balneotherapy and spa therapy on levels of cortisol as a stress biomarker: a systematic review

Balneotherapy and spa therapy are well-known practices, even though limited evidence has been produced about their biological effects. This systematic review primarily aims at assessing if balneotherapy, mud/peloid therapy, and spa therapy may influence cortisol levels. Secondarily, it aims at understanding if these interventions may improve stress resilience. PubMed/Medline, Embase, and Cochrane Library were searched for relevant articles in English or Italian about studies involving healthy and sub-healthy subjects or patients with a diagnosed disease about effects of balneotherapy, mud/peloid therapy, and spa therapy on serum and salivary cortisol levels. Fifteen studies involving 684 subjects were included. Five studies investigated biological effects of balneotherapy alone. Two of them reported significant changes of cortisol levels in healthy participants. The other three studies reported no significant variations in patients with rheumatic conditions. No studies investigated biological effects of mud/peloid therapy alone. Ten studies investigated biological effects of spa therapy with or without included mud/peloid therapy, and in all but two studies, significant variations of cortisol levels were reported. Our main findings suggest that balneotherapy may have the potential to influence cortisol levels in healthy subjects, in such a way as to improve stress resilience. Spa therapy with or without included mud/peloid therapy demonstrated the same potential to influence cortisol levels also in sub-healthy subjects and in patients with a diagnosed disease. Therefore, balneotherapy and spa therapy may be considered as useful interventions for the management of stress conditions. Further investigation is needed because of limited available data.

Placebo effects of a sham opioid solution: a randomized controlled study in patients with chronic low back pain

This study tested the experimental placebo effect in a group of chronic pain patients. Forty-eight patients having chronic back pain participated in a randomized clinical trial that tested the efficacy of a sham opioid solution (NaCl) compared with an alleged neutral, completely inactive solution (NaCl). We shaped the placebo effect by 2 interventions: verbal instruction and conditioning. The patients were either told that the "solution reduces pain and improves physical capacity" or the "solution is neutral, a placebo." Half of each group was additionally conditioned (coupling solution with reduced experimental pain), yielding 4 subgroups with 12 participants each. Outcome measures were as follows: the patients' clinical back pain ratings and acute pain ratings (both examined by numerical rating scale 0-10) and self-rated functional capacity (0%-100%; time required for the exercise). Expected pain relief before and after solution intake was also assessed. The inactive solution (NaCl), when presented as an effective treatment (sham "opioid" solution), induced placebo analgesia as evident in lower ratings of the patients' clinical back pain (F(3.12,144.21) = 25.05, P < 0.001), acute pain ratings (F(1.99,87.40) = 18.12, P < 0.01), and time needed to complete a series of daily activities exercises (F(1,44) = 8.51, P < 0.01) as well as increased functional capacity (F(1,44.00) = 19.42, P < 0.001). The 2 manipulations (instruction and conditioning) changed pain expectations, and they were maintained in both sham opioid groups. The results suggest that it may be clinically useful to explicitly integrate placebo analgesia responses into pain management.

Enhancing Placebo Effects in Somatic Symptoms Through Oxytocin

OBJECTIVE

Placebo effects relieve various somatic symptoms, but it is unclear how they can be enhanced to maximize positive treatment outcomes. Oxytocin administration may potentially enhance placebo effects, but few studies have been performed, and they have had conflicting findings. The study aim was to investigate the influence of positive verbal suggestions and oxytocin on treatment expectations and placebo effects for pain and itch.

METHODS

One hundred eight female participants were allocated to one of the following four groups: (1) oxytocin with positive verbal suggestions, (2) placebo with positive verbal suggestions, (3) oxytocin without suggestions, and (4) placebo without suggestions. The administration of 24 IU oxytocin or a placebo spray was preceded by positive verbal suggestions regarding the pain- and itch-relieving properties of the spray or no suggestions, depending on group allocation. Pain was assessed with a cold pressor test, and itch was assessed with histamine iontophoresis.

RESULTS

Positive verbal suggestions induced expectations of lower pain (F = 4.77, p = .031) and itch (F = 5.38, p = .022). Moreover, positive verbal suggestions elicited placebo analgesia (F = 5.48, p = .021) but did not decrease itch. No effect of oxytocin on the placebo effect or on expectations was found.

CONCLUSIONS

Positive suggestions induced placebo analgesia but oxytocin did not enhance the placebo effect. Study limitations are that we only included a female sample and a failure to induce placebo effect for itch. Future studies should focus on how oxytocin might influence placebo effects, taken into account the role of sex, dose-dependent effects, and various expectation manipulations.

TRIAL REGISTRATION

The study was registered as a clinical trial on www.trialregister.nl (number 6376).

Mindsets Matter: A New Framework for Harnessing the Placebo Effect in Modern Medicine

The clinical utility of the placebo effect has long hinged on physicians deceptively administering an objective placebo treatment to their patients. However, the power of the placebo does not reside in the sham treatment itself; rather, it comes from the psychosocial forces that surround the patient and the treatment. To this end, we propose a new framework for understanding and leveraging the placebo effect in clinical care. In outlining this framework, we first present the placebo effect as a neurobiological effect that is evoked by psychological processes. Next, we argue that along with implicit learning and expectation formation, mindsets are a key psychological process involved in the placebo effect. Finally, we illustrate the critical role of the social environment and treatment context in shaping these psychological processes. In doing so, we offer a guide for how the placebo effect can be understood, harnessed, and leveraged in the practice of modern medicine.

The Influence of Expectation on Nondeceptive Placebo and Nocebo Effects

Nondeceptive placebo has demonstrated its efficiency in clinical practice. Although the underlying mechanisms are still unclear, nondeceptive placebo effect and nondeceptive nocebo effect may be mediated by expectation. To examine the extent to which expectation influences these effects, the present study compared nondeceptive placebo and nocebo effects with different expectation levels. Seventy-two healthy female participants underwent a standard conditioning procedure to establish placebo and nocebo effects. Sequentially, participants were randomized to one of the four experimental groups—baseline (BL), no expectation intervention (NoEI), expectation increasing (EI), and expectation decreasing (ED) groups, to receive either no intervention or interventions through different verbal suggestions that modulated their expectation. Placebo and nocebo effects were established in all four groups after the conditioning phase. However, after disclosing the placebo and nocebo, the analgesic and the hyperalgesic effects only persisted in the EI group, when compared with the BL group. Our results provide evidence highlighting the critical role of increased expectation in nondeceptive placebo and nocebo effects. The finding suggests that open-label placebo or nocebo per se might be insufficient to induce strong analgesic or hyperalgesic response and sheds insights into administrating open-label placebo and avoiding open-label nocebo in clinical practice.

Generalization of learned pain modulation depends on explicit learning

The experience of pain is strongly influenced by contextual and socio-affective factors, including learning from previous experiences. Pain is typically perceived as more intense when preceded by a conditioned cue (CS_HIGH) that has previously been associated with higher pain intensities, compared to cues associated with lower intensities (CS_LOW). In three studies (total N=134), we tested whether this learned pain modulation generalizes to perceptually similar cues (Studies 1 and 2) and conceptually similar cues (Study 3). The results showed that participants report higher pain when heat stimulation was preceded by novel stimuli that were either perceptually (Studies 1 and 2) or conceptually (Study 3) similar to the previously conditioned CS_HIGH. In all three studies, the strength of this generalization effect was strongly correlated with individual differences in explicitly learned expectations. Together, these findings suggest an important role of conscious expectations and higher-order conceptual inference during generalization of learned pain modulation. We discuss implications for the understanding of placebo and nocebo effects as well as for chronic pain and anxiety.

A Functional-Cognitive Perspective on the Relation Between Conditioning and Placebo Research

From a functional-cognitive perspective, conditioning is relevant for placebo research because it (a) highlights stimulus pairings (e.g., taking a pill that contains an active pharmacological substance causing a drop in blood pressure) as a potential environmental cause of creating or boosting placebo effects (e.g., reduction in blood pressure after taking a similar pill that no longer contains the active substance) and (b) orients researchers to potential mental mechanisms that might underlie those effects (e.g., the formation of associations or propositions). After describing the functional-cognitive perspective on conditioning, I provide a brief overview of three generations of conditioning theories (stimulus-response, stimulus-stimulus, and propositional theories) and evaluate different ways in which conditioning and placebo research can be related. Finally, I discuss the implications of the functional-cognitive perspective on conditioning for the status of the placebo phenomenon.

The Application of Persuasion Theory to Placebo Effects

Placebo effects, or positive outcomes resulting from expectations about a treatment, are powerful components of modern medical care. In this chapter, we suggest that our understanding of placebo effects may benefit from more explicitly connecting this phenomenon to the existing empirical psychological literature on persuasion. Persuasion typically involves an attempt to bring about a change in beliefs or attitudes as a result of providing information on a topic. We begin by providing a brief overview of the psychological literature on placebo effects. We then point to connections between this literature and research on persuasive communication. Although some links have been made, these initial connections have predominantly relied on classic theories of persuasion rather than on more contemporary and comprehensive models. Next, we describe a modern theory of persuasion that may facilitate the study of placebo effects and analyze two issues pertinent to the literature on placebo effects from the lens of this model. Specifically, we consider how and when characteristics of a practitioner (e.g., variables such as perceptions of a practitioner's confidence or competence) can influence the magnitude of placebo effects, and how modern persuasion theory can help in understanding the durability of placebo effects over time. We conclude that examining placebo effects as an outcome of persuasive communication would be a fruitful line of future research.

The Underestimated Significance of Conditioning in Placebo Hypoalgesia and Nocebo Hyperalgesia

Placebo and nocebo effects are intriguing phenomena in pain perception with important implications for clinical research and practice because they can alleviate or increase pain. According to current theoretical accounts, these effects can be shaped by verbal suggestions, social observational learning, and classical conditioning and are necessarily mediated by explicit expectation. In this review, we focus on the contribution of conditioning in the induction of placebo hypoalgesia and nocebo hyperalgesia and present accumulating evidence that conditioning independent from explicit expectation can cause these effects. Especially studies using subliminal stimulus presentation and implicit conditioning (i.e., without contingency awareness) that bypass the development of explicit expectation suggest that conditioning without explicit expectation can lead to placebo and nocebo effects in pain perception. Because only few studies have investigated clinical samples, the picture seems less clear when it comes to patient populations with chronic pain. However, conditioning appears to be a promising means to optimize treatment. In order to get a better insight into the mechanisms of placebo and nocebo effects in pain and the possible benefits of conditioning compared to explicit expectation, future studies should carefully distinguish both methods of induction.

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.

Something out of nothing: the placebo effect

The history of the concept of the placebo effect and research into its quantification and mechanisms are reviewed, particularly in relation to psychiatry. Research has demonstrated a notable placebo effect in depression: a large proportion of the clinical effect of antidepressant medication is attributable to the effect. Various mechanisms have been hypothesised: anxiety relief, expectation, transference, ‘meaning effects' and conditioning. Recent research from neuroimaging has unveiled that the effect is associated with biological correlates in the brain. Despite the renewal of research into the placebo effect, many questions remain unanswered. This partly reflects philosophical obstacles such as the mind/body dichotomy, which are inherent in conceptualising the effect. However, it also demonstrates the vast scope for further research into this area. Ultimately, an understanding of the processes that underlie the placebo effect should allow a rationalised therapeutic approach to be developed to maximise the clinical benefit of the therapeutic encounter.

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.

Mental Training for Better Achievement: Effects of Verbal Suggestions and Evaluation (of Effectiveness) on Cognitive Performance

Objective: There is only some literature regarding the influence of verbal suggestions on cognitive performance in healthy volunteers. For example, the performance in a knowledge test was enhanced when participants were told that they had subliminally received the correct answer. However, enhancing cognitive performance only via verbal suggestions without prior conditioning phases has not yet been examined. The goal of our study was therefore to investigate the effects of a mental training based on verbal suggestions compared to a control training on cognitive performance in a student population using a balanced-placebo-design. Methods: In total, 103 participants were randomly assigned either to listening to a 20 min audio-taped mental training or to a 20 min philosophy lecture (control training) via headphones. Participants were individually tested before and after the training concerning their cognitive performance. Information about the type of training were varied in both intervention conditions ("You are part of our experimental condition and you will receive an effective mental training" or "You are part of our control group and you will receive the control condition"). At the end of the assessment, participants were asked what kind of training they believed they had received and how effective they would rate the received training. Results: Overall, the cognitive performance improved in all participants, F _{(1, 99)} = 490.01, p < 0.001. Contrary to our hypotheses, we found no interaction of the type of training and type of instruction on the cognitive performance. Participants who rated the received training as being effective at the end of the experiment (regardless if it was the mental or the control training), have before experienced a greater improvement in their cognitive performance [F _(2,100) = 7.26, p = 0.001] and showed higher scores in the ability to absorb [F _{(2, 99)} = 3.75, p = 0.027]. Conclusion: The subjects' own experiences in the task might have influenced the rating of the training rather than the actual training or the information they receive regarding the type of training. This finding underlines the relevance of enhancing the subjective beliefs and self-efficacy in situations where cognitive attention processes are important and of individually tailoring mental trainings.

Expectancy Reduces Symptoms but not Functional Impairment Following Exercise-induced Musculoskeletal Injury

OBJECTIVES

To quantify the extent to which the participant-provider interaction influences the response to sham treatment following exercised-induced acute musculoskeletal pain.

MATERIALS AND METHODS

In total, 40 participants between the ages of 18 and 35 volunteered for the study. Participants came to the laboratory for 3 test sessions 48-hour apart (day 1, 3, and 5). During the initial session, baseline measures were assessed and participants underwent a fatigue protocol for the biceps brachii. Participants were then assigned to a positive expectation or a no-expectation condition before receiving a sham laser therapy treatment. The positive expectation group received symptom improvement priming before their sham treatment. Participants allocated to the no-expectation condition received no feedback before the sham treatment. Maximum voluntary isometric contraction; relaxed elbow angle; visual analog scale; and the QuickDash questionnaire were used as outcome measures.

RESULTS

The positive expectation group had a significant reduction in perceived pain compared with the no-expectation group at day 3 follow-up, with the mean scores being 34.65 mm (SE=4.44) compared with 49.4 mm (SE=5.79), respectively. There were no between-group differences with respect to maximum voluntary isometric contraction, QuickDash, or relaxed elbow angle outcomes. In addition, there were no significant between-group differences observed with expected pain on follow-up visits, the effect sizes were d=0.26 on day 1 for day 3 and d=0.51 on day for day 5.

DISCUSSION

Positive expectations before a sham treatment enhanced reduction in pain intensity but did not improve functional impairments following exercise-induced acute musculoskeletal injury.

Mechanisms of placebo analgesia: A dual-process model informed by insights from cross-species comparisons

Placebo treatments are pharmacologically inert, but are known to alleviate symptoms across a variety of clinical conditions. Associative learning and cognitive expectations both play important roles in placebo responses, however we are just beginning to understand how interactions between these processes lead to powerful effects. Here, we review the psychological principles underlying placebo effects and our current understanding of their brain bases, focusing on studies demonstrating both the importance of cognitive expectations and those that demonstrate expectancy-independent associative learning. To account for both forms of placebo analgesia, we propose a dual-process model in which flexible, contextually driven cognitive schemas and attributions guide associative learning processes that produce stable, long-term placebo effects. According to this model, the placebo-induction paradigms with the most powerful effects are those that combine reinforcement (e.g., the experience of reduced pain after placebo treatment) with suggestions and context cues that disambiguate learning by attributing perceived benefit to the placebo. Using this model as a conceptual scaffold, we review and compare neurobiological systems identified in both human studies of placebo analgesia and behavioral pain modulation in rodents. We identify substantial overlap between the circuits involved in human placebo analgesia and those that mediate multiple forms of context-based modulation of pain behavior in rodents, including forebrain-brainstem pathways and opioid and cannabinoid systems in particular. This overlap suggests that placebo effects are part of a set of adaptive mechanisms for shaping nociceptive signaling based on its information value and anticipated optimal response in a given behavioral context.

Differential Classical Conditioning of the Nocebo Effect: Increasing Heat-Pain Perception without Verbal Suggestions

Background: Nocebo effects, including nocebo hyperalgesia, are a common phenomenon in clinical routine with manifold negative consequences. Both explicit expectations and learning by conditioning are known to induce nocebo effects, but the specific role of conditioning remains unclear, because conditioning is rarely implemented independent of verbal suggestions. Further, although pain is a multidimensional phenomenon, nocebo effects are usually assessed in subjective ratings only, neglecting, e.g., behavioral aspects. The aim of this study was to test whether nocebo hyperalgesia can be learned by conditioning without explicit expectations, to assess nocebo effects in different response channels, and to exploratively assess, whether contingency awareness is a necessary condition for conditioned nocebo hyperalgesia. Methods: Twenty-one healthy volunteers were classically conditioned using painful and non-painful heat stimuli that followed two different cues. The conditioned nocebo effect was assessed by subjective ratings of perceived stimulation intensity on a visual analog scale and a behavioral discrimination task, assessing sensitization and habituation in response to the same stimulation following the two cues. Results: Results show a conditioned nocebo effect indicated by the subjective intensity ratings. Conditioned effects were also seen in the behavioral responses, but paradoxically, behavioral responses indicated decreased perception after conditioning, but only for subjects successfully conditioned as indicated by the subjective ratings. Explorative analyses suggested that awareness of the contingencies and the different cues was not necessary for successful conditioning. Conclusion: Nocebo effects can be learned without inducing additional explicit expectations. The dissociation between the two response channels, possibly representing the conditioned and a compensatory response, highlights the importance of considering different outcomes in nocebo responses to fully understand underlying mechanisms. The present results challenge the role of explicit expectations in conditioned nocebo effects and are relevant with implications in clinical contexts, e.g., when transient adverse effects become conditioned.

Plasma cortisol response cannot be classically conditioned in a taste-endocrine paradigm in humans

RATIONALE

Peripheral immune responses can be modified by associative learning procedures. Less is known, however, whether and to what extent neuroendocrine parameters can be classically conditioned.

OBJECTIVES

In this randomized double-blind study, we modified an established paradigm to behaviorally condition endocrine responses in humans.

METHODS

Thirty-one healthy male participants received a distinctively flavored green drink as the conditioned stimulus (CS) and intravenous injections of corticotropin-releasing hormone (CRH) (CRH group, N = 17) or NaCl (placebo group, N = 14) as the unconditioned stimulus (US) during two subsequent acquisition trials. Plasma levels of cortisol and noradrenaline, heart rate, and psychological parameters were analyzed before and 15, 30, 60, 120, and 180 min after injection. The two acquisition trials were followed by two evocation trials, during which participants underwent the same procedure but now receiving NaCl injections.

RESULTS

CRH administration induced pronounced increases in cortisol and noradrenaline plasma concentrations, heart rate, and anxiety levels. However, re-exposure to the CS during evocations trials did not provoke conditioned increases in neuroendocrine parameters. Median split of the CRH group based on the cortisol baseline level into "cort-high" and "cort-low" subgroups showed that the "cort-high" subgroup displayed a significantly increased cortisol production on evocation days compared to the "cort-low" subgroup and the placebo group.

CONCLUSION

This taste-endocrine paradigm employing CRH injection as the US in healthy male volunteers failed to induce a behaviorally conditioned cortisol release as a learned endocrine response. Future studies should clarify a possible role of higher baseline cortisol levels in perhaps facilitating a conditioned cortisol response.

Impact of patient information leaflets on pain medication intake behavior: a pilot study

Negative wording in package information leaflets of pain medication is associated with a tendency to evoke negative emotions and lower willing to take medication.

Introduction:

Patient information leaflets on pain medication primarily list side effects while positive effects and action mechanisms remain underrepresented. Nocebo research has shown that negative instructions can lower analgesic effects.

Objectives:

Research on information leaflets and their influence on mood, memory of side effects, and intake behavior of healthy participants is needed.

Methods:

To determine the ratio of positive to negative phrases, 18 information leaflets of common, over-the-market analgesics were examined of which 1 was selected. In a randomized, controlled study design, 18 healthy participants read this leaflet while 18 control group participants read a matched, neutral leaflet of an electrical device. Collected data concerned the recall of positive and negative contents, mood, anxiety, and the willingness to buy and take the drug.

Results:

All examined leaflets listed significantly more side effects than positive effects (t₁₇ = 5.82, P < 0.01). After reading the analgesic leaflet, participants showed a trend towards more negative mood (F_1,34 = 3.78, P = 0.06, η_p² = 0.1), a lower intention to buy [χ² (1, n = 36) = 12.5, P < 0.01], a higher unwillingness to take the medication [χ² (1, n = 36) = 7.2, P < 0.01], and even a greater recall for side effects than positive effects (t₁₇ = 7.47, P < 0.01).

Conclusion:

Reading the patient information leaflets can increase fear and lower the intention to buy and the willingness to take a pain medication.

Classical conditioning without verbal suggestions elicits placebo analgesia and nocebo hyperalgesia

The aim of this study was to examine the relationships among classical conditioning, expectancy, and fear in placebo analgesia and nocebo hyperalgesia. A total of 42 healthy volunteers were randomly assigned to three groups: placebo, nocebo, and control. They received 96 electrical stimuli, preceded by either orange or blue lights. A hidden conditioning procedure, in which participants were not informed about the meaning of coloured lights, was performed in the placebo and nocebo groups. Light of one colour was paired with pain stimuli of moderate intensity (control stimuli), and light of the other colour was paired with either nonpainful stimuli (in the placebo group) or painful stimuli of high intensity (in the nocebo group). In the control group, both colour lights were followed by control stimuli of moderate intensity without any conditioning procedure. Participants rated pain intensity, expectancy of pain intensity, and fear. In the testing phase, when both of the coloured lights were followed by identical moderate pain stimuli, we found a significant analgesic effect in the placebo group, and a significant hyperalgesic effect in the nocebo group. Neither expectancy nor fear ratings predicted placebo analgesia or nocebo hyperalgesia. It appears that a hidden conditioning procedure, without any explicit verbal suggestions, elicits placebo and nocebo effects, however we found no evidence that these effects are predicted by either expectancy or fear. These results suggest that classical conditioning may be a distinct mechanism for placebo and nocebo effects.

The Cognitive Neuroscience of Placebo Effects: Concepts, Predictions, and Physiology

Placebos have been used ubiquitously throughout the history of medicine. Expectations and associative learning processes are important psychological determinants of placebo effects, but their underlying brain mechanisms are only beginning to be understood. We examine the brain systems underlying placebo effects on pain, autonomic, and immune responses. The ventromedial prefrontal cortex (vmPFC), insula, amygdala, hypothalamus, and periaqueductal gray emerge as central brain structures underlying placebo effects. We argue that the vmPFC is a core element of a network that represents structured relationships among concepts, providing a substrate for expectations and a conception of the situation-the self in context-that is crucial for placebo effects. Such situational representations enable multidimensional predictions, or priors, that are combined with incoming sensory information to construct percepts and shape motivated behavior. They influence experience and physiology via descending pathways to physiological effector systems, including the spinal cord and other peripheral organs.

Tetrahydrocannabinol Does Not Reduce Pain in Patients With Chronic Abdominal Pain in a Phase 2 Placebo-controlled Study

BACKGROUND & AIMS

Delta-9-tetrahydrocannabinol (THC) is the most abundant cannabinoid from the plant Cannabis sativa. There is only equivocal evidence that THC has analgesic effects. We performed a phase 2 controlled trial to evaluate the analgesic efficacy, pharmacokinetics, safety, and tolerability of an oral tablet containing purified THC in patients with chronic abdominal pain.

METHODS

Sixty-five patients with chronic abdominal pain for 3 months or more (numeric rating scale scores of 3 or more) after surgery or because of chronic pancreatitis were randomly assigned to groups given the THC tablet or identical matching placebos for 50-52 days. Subjects in the THC group were given the tablet first in a step-up phase (3 mg 3 times daily for 5 days and then 5 mg 3 times daily for 5 days), followed by a stable dose phase (8 mg 3 times daily until days 50-52). Preceding and during the entire study period, patients were asked to continue taking their medications (including analgesics) according to prescription. Patients reported any additional pain medications in a diary. Efficacy and safety assessments were conducted preceding medication intake (day 1), after 15 days, and at 50-52 days. Plasma samples were collected on study days 1, 15, and 50-52; mean plasma concentration curves of THC and 11-OH-THC were plotted. The primary end point was pain relief, which was measured by a visual analogue scale (VAS) of the mean pain (VAS mean scores) on the basis of information from patient diaries. Secondary end points included pain and quality of life (determined from patient questionnaires), pharmacokinetics, and safety.

RESULTS

At days 50-52, VAS mean scores did not differ significantly between the THC and placebo groups (F_1,46 = 0.016; P = .901). Between the start and end of the study, VAS mean scores decreased by 1.6 points (40%) in the THC group compared with 1.9 points (37%) in the placebo group. No differences were observed in secondary outcomes. Oral THC was generally well-absorbed. Seven patients in the THC group stopped taking the tablets because of adverse events, compared with 2 patients in the placebo group. All (possibly) related adverse events were mild or moderate.

CONCLUSIONS

In a phase 2 study, we found no difference between a THC tablet and a placebo tablet in reducing pain measures in patients with chronic abdominal pain. THC, administered 3 times daily, was safe and well-tolerated during a 50-day to 52-day treatment period. ClinicalTrials.gov number: NCT01562483 and NCT01551511.

What techniques might be used to harness placebo effects in non-malignant pain? A literature review and survey to develop a taxonomy

OBJECTIVES

Placebo effects can be clinically meaningful but are seldom fully exploited in clinical practice. This review aimed to facilitate translational research by producing a taxonomy of techniques that could augment placebo analgesia in clinical practice.

DESIGN

Literature review and survey.

METHODS

We systematically analysed methods which could plausibly be used to elicit placebo effects in 169 clinical and laboratory-based studies involving non-malignant pain, drawn from seven systematic reviews. In a validation exercise, we surveyed 33 leading placebo researchers (mean 12 years’ research experience, SD 9.8), who were asked to comment on and add to the draft taxonomy derived from the literature.

RESULTS

The final taxonomy defines 30 procedures that may contribute to placebo effects in clinical and experimental research, proposes 60 possible clinical applications and classifies procedures into five domains: the patient’s characteristics and belief (5 procedures and 11 clinical applications), the practitioner’s characteristics and beliefs (2 procedures and 4 clinical applications), the healthcare setting (8 procedures and 13 clinical applications), treatment characteristics (8 procedures and 14 clinical applications) and the patientâ€"practitioner interaction (7 procedures and 18 clinical applications).

CONCLUSION

The taxonomy provides a preliminary and novel tool with potential to guide translational research aiming to harness placebo effects for patient benefit in practice.

Placebo-related effects: a meta-narrative review of conceptualization, mechanisms and their relevance in rheumatology

For decades in medicine, the placebo effect has been conceptualized as a subjective psychological effect associated with an inert substance and considered to be a nuisance noise in the assessment of therapeutic effects in clinical trials. However, research on placebo has undergone substantial developments since the mid-1980s in several fields of knowledge (including methodology, psychology and neurosciences) that challenge this traditional view. Using a meta-narrative approach, this review of conceptualizations, determinants, mechanisms and models of placebo effects shows that placebo effects are genuine biopsychosocial phenomena strongly affected by context and factors surrounding the patient and treatments. Psychological experiments and neurobiological and neuroimaging studies have identified various types of placebo responses, driven by different mechanisms (especially but not only expectation and conditioning) and associated with different chemical, structural and functional features. Insights into the mechanisms involved in placebo responses have led to opportunities for ethical enhancements of these mechanisms in clinical practice, notably by improving the patient-doctor interaction and refining the therapeutic ritual. These developments should be carefully considered in rheumatology settings, in which placebo effects are both prevalent and significant, with the potential to improve patient care.

Placebo and nocebo reactions in randomized trials of pharmacological treatments for persistent depressive disorder. A meta-regression analysis

BACKGROUND

We aimed to investigate placebo and nocebo reactions in randomized controlled trials (RCT) of pharmacological treatments for persistent depressive disorder (PDD).

METHODS

We conducted a systematic electronic search and included RCTs investigating antidepressants for the treatment of PDD. Outcomes were the number of patients experiencing response and remission in placebo arms (=placebo reaction). Additional outcomes were the incidence of patients experiencing adverse events and related discontinuations in placebo arms (=nocebo reaction). A priori defined effect modifiers were analyzed using a series of meta-regression analyses.

RESULTS

Twenty-three trials were included in the analyses. We found a pooled placebo response rate of 31% and a placebo remission rate of 22%. The pooled adverse event rate and related discontinuations were 57% and 4%, respectively. All placebo arm outcomes were positively associated with the corresponding medication arm outcomes. Placebo response rate was associated with a greater proportion of patients with early onset depression, a smaller chance to receive placebo and a larger sample size. The adverse event rate in placebo arms was associated with a greater proportion of patients with early onset depression, a smaller proportion of females and a more recent publication.

CONCLUSIONS

Pooled placebo and nocebo reaction rates in PDD were comparable to those in episodic depression. The identified effect modifiers should be considered to assess unbiased effects in RCTs, to influence placebo and nocebo reactions in practice.

LIMITATIONS

Limitations result from the methodology applied, the fact that we conducted only univariate analyses, and the number and quality of included trials.

Placebo response in pain, fatigue, and performance: Possible implications for neuromuscular disorders

The placebo response in neuromuscular disorders is not well understood. The only available data regarding its underlying mechanisms are related to neuropathic pain. In this review, we describe the factors that contribute to improved outcomes in the placebo arm, with specific attention to pain and fatigue, as well as some of the most important psychobiological mechanisms that may explain such a response. This approach may also improve our insight into the symptomatology and therapeutic responses of other neuromuscular disorders. The fact that >90% of tested analgesics for neuropathic pain have failed in advanced phases of clinical trials should prompt a greater investment of effort and resources into understanding the mechanisms and impact of placebos in clinical research. Such an endeavor will help improve the design of clinical trials and will provide information that informs clinical neuromuscular practice. Muscle Nerve 56: 358-367, 2017.

Brain Mechanisms of the Placebo Effect: An Affective Appraisal Account

Placebos are sham medical treatments. Nonetheless, they can have substantial effects on clinical outcomes. Placebos depend on a person's psychological and brain responses to the treatment context, which influence appraisals of future well-being. Appraisals are flexible cognitive evaluations of the personal meaning of events and situations that can directly impact symptoms and physiology. They also shape associative learning processes by guiding what is learned from experience. Appraisals are supported by a core network of brain regions associated with the default mode network involved in self-generated emotion, self-evaluation, thinking about the future, social cognition, and valuation of rewards and punishment. Placebo treatments for acute pain and a range of clinical conditions engage this same network of regions, suggesting that placebos affect behavior and physiology by changing how a person evaluates their future well-being and the personal significance of their symptoms.

An enactive account of placebo effects

Placebos are commonly defined as ineffective treatments. They are treatments that lack a known mechanism linking their properties to the properties of the condition on which treatment aims to intervene. Given this, the fact that placebos can have substantial therapeutic effects looks puzzling. The puzzle, we argue, arises from the relationship placebos present between culturally meaningful entities (such as treatments or therapies), our intentional relationship to the environment (such as implicit or explicit beliefs about a treatment's healing powers) and bodily effects (placebo responses). How can a mere attitude toward a treatment result in appropriate bodily changes? We argue that an 'enactive' conception of cognition accommodates and renders intelligible the phenomenon of placebo effects. Enactivism depicts an organism's adaptive bodily processes, its intentional directedness, and the meaningful properties of its environment as co-emergent aspects of a single dynamic system. In doing so it provides an account of the interrelations between mind, body and world that demystifies placebo effects.

Nature of the placebo and nocebo effect in relation to functional neurologic disorders

Placebos have long been considered a nuisance in clinical research, for they have always been used as comparators for the validation of new treatments. By contrast, today they represent an active field of research, and, due to the involvement of many mechanisms, the study of the placebo effect can actually be viewed as a melting pot of concepts and ideas for neuroscience. There is not a single placebo effect, but many, with different mechanisms across different medical conditions and therapeutic interventions. Expectation, anxiety, and reward are all involved, as well as a variety of learning phenomena and genetic variants. The most productive models to better understand the neurobiology of the placebo effect are pain and Parkinson's disease. In these medical conditions, several neurotransmitters have been identified, such as endogenous opioids, cholecystokinin, dopamine, as well as lipidic mediators, for example, endocannabinoids and prostaglandins. Since the placebo effect is basically a psychosocial context effect, these data indicate that different social stimuli, such as words and therapeutic rituals, may change the chemistry of the patient's brain, and these effects are similar to those induced by drugs.

Relieving pain using dose-extending placebos: a scoping review

Placebos are often used by clinicians, usually deceptively and with little rationale or evidence of benefit, making their use ethically problematic. In contrast with their typical current use, a provocative line of research suggests that placebos can be intentionally exploited to extend analgesic therapeutic effects. Is it possible to extend the effects of drug treatments by interspersing placebos? We reviewed a database of placebo studies, searching for studies that indicate that placebos given after repeated administration of active treatments acquire medication-like effects. We found a total of 22 studies in both animals and humans hinting of evidence that placebos may work as a sort of dose extender of active painkillers. Wherever effective in relieving clinical pain, such placebo use would offer several advantages. First, extending the effects of a painkiller through the use of placebos may reduce total drug intake and side effects. Second, dose-extending placebos may decrease patient dependence. Third, using placebos along with active medication, for part of the course of treatment, should limit dose escalation and lower costs. Provided that nondisclosure is preauthorized in the informed consent process and that robust evidence indicates therapeutic benefit comparable to that of standard full-dose therapeutic regimens, introducing dose-extending placebos into the clinical arsenal should be considered. This novel prospect of placebo use has the potential to change our general thinking about painkiller treatments, the typical regimens of painkiller applications, and the ways in which treatments are evaluated.

Nocebo and pain: An overview of the psychoneurobiological mechanisms

INTRODUCTION

Nocebo effects are defined as adverse events related to negative expectations and learning processes that are involved in the modulation of the descending pain pathways. Research over the last couple of decades has illustrated that behavioral, psychoneurobiological and functional changes occur during nocebo-induced pain processing.

OBJECTIVES

We aimed to review published human and non-human research on algesia and hyperalgesia resulting from negative expectations and nocebo effects.

METHODS

Herein, we searched and comprehensively reviewed scientific literature providing informative knowledge about the psychoneurobiological bases of the nocebo effect in the field of pain with an emphasis on how pain processes are shaped by both cognitive and non-cognitive factors.

RESULTS

Negative expectations are formed through verbal suggestions of heightened pain, prior nociceptive and painful experiences and observation of pain in others. Susceptibility to the nocebo effect can be also influenced by genetic variants, conscious and nonconscious learning processes, personality traits and psychological factors. Moreover, providers' behaviors, environmental cues and the appearance of medical devices can induce negative expectations that dramatically influence pain perception and processing in a variety of pain modalities and patient populations.

CONCLUSION

Importantly, we concluded that nocebo studies outline how individual expectations may lead to physiological changes underpinning the central integration and processing of magnified pain signaling. Further research is needed to develop strategies that can identify nocebo-vulnerable pain patients in order to optimize the psychosocial and therapeutic context in which the clinical encounter occurs, with the ultimate purpose of improving clinical outcomes.

Bayesian prediction of placebo analgesia in an instrumental learning model

Placebo analgesia can be primarily explained by the Pavlovian conditioning paradigm in which a passively applied cue becomes associated with less pain. In contrast, instrumental conditioning employs an active paradigm that might be more similar to clinical settings. In the present study, an instrumental conditioning paradigm involving a modified trust game in a simulated clinical situation was used to induce placebo analgesia. Additionally, Bayesian modeling was applied to predict the placebo responses of individuals based on their choices. Twenty-four participants engaged in a medical trust game in which decisions to receive treatment from either a doctor (more effective with high cost) or a pharmacy (less effective with low cost) were made after receiving a reference pain stimulus. In the conditioning session, the participants received lower levels of pain following both choices, while high pain stimuli were administered in the test session even after making the decision. The choice-dependent pain in the conditioning session was modulated in terms of both intensity and uncertainty. Participants reported significantly less pain when they chose the doctor or the pharmacy for treatment compared to the control trials. The predicted pain ratings based on Bayesian modeling showed significant correlations with the actual reports from participants for both of the choice categories. The instrumental conditioning paradigm allowed for the active choice of optional cues and was able to induce the placebo analgesia effect. Additionally, Bayesian modeling successfully predicted pain ratings in a simulated clinical situation that fits well with placebo analgesia induced by instrumental conditioning.

Applications and limitations of behaviorally conditioned immunopharmacological responses

The importance of placebo responses for the treatment of various medical conditions has increasingly been recognized, whereas knowledge and systematic application in clinical settings are still sparse. One possible application for placebo responses in pharmacotherapy is given by learning paradigms, such as behaviorally conditioned immunosuppression, aiming at drug dose reduction while maintaining therapeutic efficacy of drug treatment. In an established learning paradigm of conditioned taste aversion/avoidance (CTA) in both, rats and humans, respectively, a novel-tasting drinking solution (conditioned stimulus, CS) is paired with an injection of the immunosuppressive drug cyclosporine A (CsA) as unconditioned stimulus (US). The conditioned response, evoked by re-presenting the CS alone at a later time, is reflected by avoidance behavior of consuming the solution (conditioned taste aversion; CTA) and a diminished interleukin (IL)-2 and interferon (IFN)-γ cytokine production as well as mRNA expression of rat splenic T cells or human peripheral T lymphocytes, closely mimicking the immunosuppressive effects of CsA. However, due to unreinforced CS-re-exposure conditioned responses progressively decreases over time (extinction), reflecting a considerable challenge for potential clinical applications of this learned immunosuppression. The present article discusses and critically reviews actual approaches, applications but also limitations of learning paradigms in immune pharmacotherapy.

A Review of the Theoretical and Biological Understanding of the Nocebo and Placebo Phenomena

PURPOSE

Placebos are commonly used in experimental and patient populations and are known to influence treatment outcomes. The mechanism of action of placebos has been investigated by several researchers. This review investigates the current knowledge regarding the theoretical and biological underpinning of the nocebo and placebo phenomena.

METHOD

Literature was searched using PubMed using the following keywords: nocebo, placebo, μ-opioid, dopamine, conditioning, and expectancy. Relevant papers were selected for review by the authors.

FINDINGS

The roles of conditioning and expectancy, and characteristics associated with nocebo and placebo responses, are discussed. These factors affect nocebo and placebo responses, although their effect sizes vary greatly, depending on inter-individual differences and different experimental paradigms. The neurobiology of the nocebo and placebo phenomena is also reviewed, emphasizing the involvement of reward pathways, such as the μ-opioid and dopamine pathways. Neurobiological pathways have been investigated in a limited range of experimental paradigms, with the greatest efforts on experimental models of placebo analgesia. The interconnectedness of psychological and physiological drivers of nocebo and placebo responses is a core feature of these phenomena.

IMPLICATIONS

Further research is needed to fully understand the underpinnings of the nocebo and placebo phenomena. Neurobiology pathways need to be investigated in experimental paradigms that model the placebo response to a broader range of pathologies. Similarly, although many psychological factors and inter-individual characteristics have been identified as significant mediators and moderators of nocebo and placebo responses, the factors identified to date are unlikely to be exhaustive.

Placebo Intervention Enhances Reward Learning in Healthy Individuals

According to the placebo-reward hypothesis, placebo is a reward-anticipation process that increases midbrain dopamine (DA) levels. Reward-based learning processes, such as reinforcement learning, involves a large part of the DA-ergic network that is also activated by the placebo intervention. Given the neurochemical overlap between placebo and reward learning, we investigated whether verbal instructions in conjunction with a placebo intervention are capable of enhancing reward learning in healthy individuals by using a monetary reward-based reinforcement-learning task. Placebo intervention was performed with non-invasive brain stimulation techniques. In a randomized, triple-blind, cross-over study we investigated this cognitive placebo effect in healthy individuals by manipulating the participants’ perceived uncertainty about the intervention’s efficacy. Volunteers in the purportedly low- and high-uncertainty conditions earned more money, responded more quickly and had a higher learning rate from monetary rewards relative to baseline. Participants in the purportedly high-uncertainty conditions showed enhanced reward learning, and a model-free computational analysis revealed a higher learning rate from monetary rewards compared to the purportedly low-uncertainty and baseline conditions. Our results indicate that the placebo response is able to enhance reward learning in healthy individuals, opening up exciting avenues for future research in placebo effects on other cognitive functions.

Pain: A Statistical Account

Perception is seen as a process that utilises partial and noisy information to construct a coherent understanding of the world. Here we argue that the experience of pain is no different; it is based on incomplete, multimodal information, which is used to estimate potential bodily threat. We outline a Bayesian inference model, incorporating the key components of cue combination, causal inference, and temporal integration, which highlights the statistical problems in everyday perception. It is from this platform that we are able to review the pain literature, providing evidence from experimental, acute, and persistent phenomena to demonstrate the advantages of adopting a statistical account in pain. Our probabilistic conceptualisation suggests a principles-based view of pain, explaining a broad range of experimental and clinical findings and making testable predictions.

A Comparison of Deceptive and Non-Deceptive Placebo Analgesia: Efficacy and Ethical Consequences

BACKGROUND

Research has demonstrated the efficacy of analgesic placebos. The manner in which they are usually delivered deceptively raises questions about their impact on recipients. However, there has been little empirical investigation into the potential harms of analgesic placebo. Moreover, the role of deception in determining the magnitude of analgesic placebo response remains poorly understood.

PURPOSE

This study aimed to investigate the consequences of deceptive placebo analgesia in terms of ethical/psychological effects and efficacy.

METHODS

Healthy adults (N = 75) were randomized to a control group, deceptive placebo manipulation, or non-deceptive placebo manipulation. All participants underwent repeated pain testing using a thermal stimulus. Placebo manipulation groups underwent placebo conditioning involving a cream that was described as being either analgesic or inert. State-specific negative mood and attitudes toward research and pain treatment were assessed before and after placebo conditioning.

RESULTS

Deceptive and non-deceptive placebo manipulations yielded pain ratings that did not differ significantly from one another but did differ from those of the control group, which experienced a pain sensitization response across trials. Results thus indicated that both deceptive and non-deceptive placebo manipulations prevented pain sensitization. Across groups, the participants reported improved depression, anxiety, frustration, and fear. The use of placebo did not negatively impact participants' attitudes and beliefs about research or pain treatments. The participants tended to rate several parameters related to research participation more positively after participating in our study.

CONCLUSIONS

Our results indicate that the placebo manipulation groups experienced an anti-sensitization effect. The use of analgesic placebo did not result in any detrimental ethical or psychological effects.

The power and value of placebo and nocebo in painful osteoarthritis

This paper reviews some recent advances in our understanding of the effects of sham or dummy interventions on pain and other symptoms in osteoarthritis (OA), and outlines two new approaches to the investigation of placebo and nocebo effects. We argue that the placebo effect provides us with a valuable way of investigating the nature of conditions like OA. For example, by examining which symptoms, biochemical markers or imaging features do or do not respond to placebo, we might learn more about the relationships between pathology and symptoms in OA. Placebo and nocebo effects are positive or negative outcomes resulting from the human interactions and contexts in which healthcare consultations take place. Subtle changes in behaviours and the environments in which consultations take place can have major effects on pain and other symptoms being experienced by people with OA. Nocebo effects are particularly powerful, leading to many health-care professionals (HCPs) causing unintended harm to their clients. Based on our own research, we conclude that beneficial outcomes are most likely to occur when both the (HCP) and the client feel safe and relaxed, and when the experiences of the client are validated by the (HCP). These findings have important implications for clinical practice. We believe that research in this field needs to be 'trans-disciplinary', escaping from the constraints of the purely biomedical, deterministic, positivist paradigm of most medical research. We provide the example of our own work which combines performance studies and scholarship, with psychology and medicine.

Placebo, nocebo, and neuropathic pain

Over the last decade, the apparent increase in placebo responses in randomized controlled trials (RCTs) of neuropathic pain have complicated and potentially limited development and availability of new effective pain medication. Placebo analgesia and nocebo hyperalgesia effects are well described in nociceptive and idiopathic pain conditions, but less is known about the magnitude and mechanisms of placebo and nocebo effects in neuropathic pain. In neuropathic pain, placebo treatments have primarily been used as control conditions for active agents under investigation in RCTs and these placebo responses are typically not controlled for the natural history of pain and other confounding factors. Recently, mechanistic studies that control for the natural history of pain have investigated placebo and nocebo effects in neuropathic pain in their own right. Large placebo analgesia but no nocebo hyperalgesic effects have been found, and the underlying mechanisms are beginning to be elucidated. Here we review placebo and nocebo effects and the underlying mechanisms in neuropathic pain and compare them with those of nociceptive and idiopathic pain. This allows for a novel discussion on how knowledge of psychological, neurobiological, and genetic factors underlying well-controlled placebo effects may help improve the information that can be obtained from and potentially restore the utility of RCTs.