Inducing placebo respiratory depressant responses in humans via opioid receptors

A Fictionalist Account of Open-Label Placebo

The placebo effect is now generally defined widely as an individual's response to the psychosocial context of a clinical treatment, as distinct from the treatment's characteristic physiological effects. Some researchers, however, argue that such a wide definition leads to confusion and misleading implications. In response, they propose a narrow definition restricted to the therapeutic effects of deliberate placebo treatments. Within the framework of modern medicine, such a scope currently leaves one viable placebo treatment paradigm: the non-deceptive and non-concealed administration of "placebo pills" or open-label placebo (OLP) treatment. In this paper, I consider how the placebo effect occurs in OLP. I argue that a traditional, belief-based account of OLP is paradoxical. Instead, I propose an account based on the non-doxastic attitude of pretence, understood within a fictionalist framework.

Can Pharmacological Conditioning as an Add-On Treatment Optimize Standard Pharmacological Treatment in Patients with Recent-Onset Rheumatoid Arthritis? A Proof-of-Principle Randomized Clinical Trial

Medication regimens using conditioning via variable reinforcement have shown similar or improved therapeutic effects as full pharmacological treatment, but evidence in patient populations is scarce. This proof-of-principle double-blind randomized clinical trial examined whether treatment effects in recent-onset rheumatoid arthritis (RA) can be optimized through pharmacological conditioning. After four months of standardized treatment (n = 46), patients in clinical remission (n = 19) were randomized to the Control group (C), continuing standardized treatment (n = 8), or the Pharmacological Conditioning (PC) group, receiving variable treatment according to conditioning principles (n = 11). After eight months, treatment was tapered and discontinued linearly (C) or variably (PC). Standard treatment led to large improvements in disease activity and HRQoL in both groups. The groups did not differ in the percentage of drug-free clinical remission obtained after conditioning or continued standard treatment. The PC group did show a larger decrease in self-reported disease activity (Cohen's d = 0.9) and a smaller increase in TNF-α levels (Cohen's d = 0.7) than the C group. During all phases, more differences between groups were found for the patients who followed protocol than for the intention-to-treat sample. Although the results are not conclusive, pharmacological conditioning may have some advantages in terms of disease progression and stability, especially during the conditioning phase, compared with standard clinical treatment. The effects may be particularly beneficial for patients who show a good initial response to increased medication dosages.

Lack of Effects of the Presence of a Dog on Pain Perception in Healthy Participants-A Randomized Controlled Trial

Animal-assisted interventions (AAIs) have been shown to be effective in the treatment of pain. Studies suggest that relationships with animals can have comparable qualities to relationships with humans and that this enables animals to provide social support. Further, the presence of an animal can strengthen the therapeutic alliance between patients and treatment providers. This suggests that the analgesic effects of AAI might be mediated by social support from an animal or by strengthening the alliance between the patient and the treatment provider. To test these assumptions, we examined the effects of the presence of a dog on experimentally induced pain in a pain assessment and a pain therapy context. Hundred thirty-two healthy participants were randomly assigned to the conditions “pain,” “pain + dog,” “pain + placebo,” or “pain + placebo + dog.” We collected baseline and posttreatment measurements of heat-pain tolerance and the heat-pain threshold and of the corresponding subjective ratings of heat-pain intensity and unpleasantness as well as of participants' perceptions of the study investigator. The primary outcome was heat-pain tolerance. The presence of the dog did not influence the primary outcome (“pain” vs. “pain + dog”: difference = 0.04, CI = −0.66 to 0.74, p = 0.905; “pain + placebo” vs. “pain + placebo + dog”: difference = 0.43, CI = −0.02 to 0.88, p = 0.059). Participants did also not perceive the study investigator to be more trustworthy in the presence of the dog (“pain” vs. “pain + dog”: difference = 0.10, CI = −0.67 to 0.87, p = 0.796; “pain + placebo” vs. “pain + placebo + dog”: difference = 0.11, CI = −0.43 to 0.64, p = 0.695). The results indicate that the mere presence of a dog does not contribute to pain reduction and that the analgesic effects of AAI that previous studies have found is not replicated in our study as AAI did not increase perceived social support and had no effect on the alliance between the participant and the treatment provider. We assume that the animal most likely needs to be an integrated and plausible part of the treatment rationale so that participants are able to form a treatment-response expectation toward AAI.

Clinical Trial Registration: This study was preregistered as a clinical trial on www.clinicaltrials.gov (Identifier: NCT0389814).

Placebo From an Enactive Perspective

Due to their complexity and variability, placebo effects remain controversial. We suggest this is also due to a set of problematic assumptions (dualism, reductionism, individualism, passivity). We critically assess current explanations and empirical evidence and propose an alternative theoretical framework-the enactive approach to life and mind-based on recent developments in embodied cognitive science. We review core enactive concepts such as autonomy, agency, and sense-making. Following these ideas, we propose a move from binary distinctions (e.g., conscious vs. non-conscious) to the more workable categories of reflective and pre-reflective activity. We introduce an ontology of individuation, following the work of Gilbert Simondon, that allow us to see placebo interventions not as originating causal chains, but as modulators and triggers in the regulation of tensions between ongoing embodied and interpersonal processes. We describe these interrelated processes involving looping effects through three intertwined dimensions of embodiment: organic, sensorimotor, and intersubjective. Finally, we defend the need to investigate therapeutic interactions in terms of participatory sense-making, going beyond the identification of individual social traits (e.g., empathy, trust) that contribute to placebo effects. We discuss resonances and differences between the enactive proposal, popular explanations such as expectations and conditioning, and other approaches based on meaning responses and phenomenological/ecological ideas.

The placebo effect: To explore or to exploit?

How people choose between options with differing outcomes (explore-exploit) is a central question to understanding human behaviour. However, the standard explore-exploit paradigm relies on gamified tasks with low-stake outcomes. Consequently, little is known about decision making for biologically-relevant stimuli. Here, we combined placebo and explore-exploit paradigms to examine detection and selection of the most effective treatment in a pain model. During conditioning, where 'optimal' and 'suboptimal' sham-treatments were paired with a reduction in electrical pain stimulation, participants learnt which treatment most successfully reduced pain. Modelling participant responses revealed three important findings. First, participants' choices reflected both directed and random exploration. Second, expectancy modulated pain - indicative of recursive placebo effects. Third, individual differences in terms of expectancy during conditioning predicted placebo effects during a subsequent test phase. These findings reveal directed and random exploration when the outcome is biologically-relevant. Moreover, this research shows how placebo and explore-exploit literatures can be unified.

The placebo phenomenon and the underlying mechanisms

The clinical role of the placebo effect is a topic of increasing interest for the scientific community. Focus is shifting from the inert role of placebos in randomized controlled trials (RCTs) to potential effects in clinical applications, since the phenomenon is thought to be inherent in routine clinical practice, affecting therapy success rates. Mediation of the mind-brain-body relationship involves both psychosocial and neurobiological factors, the interaction of which comprises the placebo mechanisms. Psychosocial factors include environmentally induced expectations, reward expectations, and even conditioned responses to certain stimuli. Expectations also depend on previous experience of the patient with a similar procedure and can affect future responses. Moreover, the supportive bedside behavior of the clinician and the positive framing of information provided to the patient have proven to be of great importance, setting the foundations for reconsideration of standardized practices. Neurobiological mechanisms mediate these effects through neurotransmitter and neuromodulator pathways. The best understood mechanisms are those regulating non-opioid- and opioid-mediated analgesic responses that implicate specific brain regions of pain control and activation of endogenous opioids. Other responses concern, among others, hormonal control, motor performance, and antidepressant responses. Although mechanisms underlying placebo responses are not as yet completely elucidated, there is substantial evidence suggesting that placebo effects are indicative of healthy functioning of intact brain structures and occur through actual functional changes, and are not simply subjective symptom reports. These effects can be utilized in treatment optimization while maintaining an ethical and respectful manner toward the patient and the standardized disclosure procedures.

Incorporating methods and findings from neuroscience to better understand placebo and nocebo effects in sport

Placebo and nocebo effects are a factor in sports performance. However, the majority of published studies in sport science are descriptive and speculative regarding mechanisms. It is therefore not unreasonable for the sceptic to argue that placebo and nocebo effects in sport are illusory, and might be better explained by variations in phenomena such as motivation. It is likely that, in sport at least, placebo and nocebo effects will remain in this empirical grey area until researchers provide stronger mechanistic evidence. Recent research in neuroscience has identified a number of consistent, discrete and interacting neurobiological and physiological pathways associated with placebo and nocebo effects, with many studies reporting data of potential interest to sport scientists, for example relating to pain, fatigue and motor control. Findings suggest that placebos and nocebos result in activity of the opioid, endocannabinoid and dopamine neurotransmitter systems, brain regions including the motor cortex and striatum, and measureable effects on the autonomic nervous system. Many studies have demonstrated that placebo and nocebo effects associated with a treatment, for example an inert treatment presented as an analgesic or stimulant, exhibit mechanisms similar or identical to the verum or true treatment. Such findings suggest the possibility of a wide range of distinct placebo and nocebo mechanisms that might influence sports performance. In the present paper, we present some of the findings from neuroscience. Focussing on fatigue as an outcome and caffeine as vehicle, we propose three approaches that researchers in sport might incorporate in their studies in order to better elucidate mechanisms of placebo/nocebo effects on performance.

Pharmacological conditioning in the treatment of recent-onset rheumatoid arthritis: a randomized controlled trial study protocol

BACKGROUND

In pharmacological conditioning associations are formed between the effects of medication and contextual factors related to the medication. Pharmacological conditioning with placebo medication can result in comparable treatment effects and reduced side effects compared to regular treatment in various clinical populations, and may be applied to achieve enhanced drug effects. In the current study protocol, pharmacological conditioning is applied to achieve enhanced treatment effects in patients with recent-onset rheumatoid arthritis (RA). The results from this study broaden the knowledge on the potential of pharmacological conditioning and provide a potential innovative treatment option to optimize long-term pharmacological treatment effectiveness for patients with inflammatory conditions, such as recent-onset RA.

METHODS

A multicenter, randomized controlled clinical trial is conducted in patients with recent-onset RA. Participants start on standardized pharmacological treatment for 16 weeks, which consists of methotrexate (MTX) 15 mg/week and a tapered schedule of prednisone 60 mg or 30 mg. After 4 months, participants in clinical remission (based on the rheumatologist's opinion and a targeted score below 1.6 on a 44-joint disease activity score (DAS44)) are randomized to 1 of 2 groups: (1) the control group (C), which continues with a standardized treatment schedule of MTX 15 mg/week or (2) the pharmacological conditioning group (PC), which receives an MTX treatment schedule in alternating high and low dosages. In the case of persistent clinical remission after 8 months, treatment is tapered and discontinued linearly in the C group and variably in the PC group. Both groups receive the same cumulative amount of MTX during each period. Logistic regression analysis is used to compare the proportion of participants with drug-free clinical remission after 12 months between the C group and the PC group. Secondary outcome measures include clinical functioning, laboratory assessments, and self-reported measures after each 4-month period up to 18 months after study start.

DISCUSSION

The results from this study broaden the knowledge on the potential of pharmacological conditioning and provide a potential innovative treatment option to optimize long-term pharmacological treatment effectiveness in patients with inflammatory conditions, such as recent-onset RA.

TRIAL REGISTRATION

Netherlands Trial Register, NL5652. Registered on 3 March 2016.

Nocebo hyperalgesia induced by implicit conditioning

BACKGROUND AND OBJECTIVES

Nocebo hyperalgesia (i.e., increased pain sensitivity based on expectations) can be induced by conditioning, but is supposed to be mediated by conscious expectation. Although recent evidence points to the feasibility of subliminal conditioning of nocebo hyperalgesia with masked faces, face processing might be a special case and the practical implications of subliminal conditioning remain questionable. This study aimed to implicitly condition nocebo hyperalgesia using supraliminal cues.

METHODS

Implicit differential nocebo conditioning (N = 48 healthy participants) was implemented by coupling high and low painful electric stimuli to varying visual stimuli that only differed in the symmetry/asymmetry of one component (CS+/CS-) and contained further distracting components. In the test phase, only the low painful stimulus followed both CS to test for conditioned nocebo effects in intensity and aversiveness ratings and electrodermal activity. A behavioral contingency test and a post-experimental questionnaire assessed contingency awareness.

RESULTS

A conditioned effect emerged in the aversiveness (p = .036; η² = 0.09), but not in the intensity rating (p = .195) while controlling for contingency awareness. Further, increased skin conductance levels in response to CS + emerged, irrespective of contingency awareness (p = .014, η² = 0.13). No conditioned responses in skin conductance responses emerged (p = .872).

LIMITATIONS

Expected effects only emerged in part of the outcome variables.

CONCLUSIONS

The results support the notion that implicit conditioning of nocebo hypoalgesia is feasible using a novel experimental conditioning design with supraliminal stimulus presentation, although further research is needed. So far, implicitly conditioned nocebo effects might have been underestimated despite vast clinical implications.

Placebos in the era of open-label trials: An update for clinicians

Placebos have been used extensively by vast numbers of physicians, in a majority of clinical trials. Placebo effects involve behavioural, psychological and genetic factors and have been subject to ethical controversies stemming from the use of deception in treating patients. The patient-physician encounter, endogenous pharmacological pathways, personality traits and genetic diversity have all been reported to be key players in placebo responses. In the last decade, a new methodological paradigm of placebo research has emerged, using open-label placebos to investigate their effects which showed promising results for various common medical conditions. In this review, we will summarize the current body of evidence on placebos in clinical practice, with a view to open-label placebo trials in particular. It is our view that future larger-scale randomized blinded open placebo trials will benefit physicians and improve patient outcomes.

Pain Modulation: From Conditioned Pain Modulation to Placebo and Nocebo Effects in Experimental and Clinical Pain

Accumulating evidence reveal important applications of endogenous pain modulation assessment in healthy controls and in patients in clinical settings, as dysregulations in the balance of pain modulatory circuits may facilitate pain and promote chronification of pain. This article reviews data on pain modulation, focusing on the mechanisms and translational aspects of pain modulation from conditioned pain modulation (CPM) to placebo and nocebo effects in experimental and clinical pain. The specific roles of expectations, learning, neural and neurophysiological mechanisms of the central nervous system are briefly reviewed herein. The interaction between CPM and placebo systems in pain inhibitory pathways is highly relevant in the clinic and in randomized controlled trials yet remains to be clarified. Examples of clinical implications of CPM and its relationship to placebo and nocebo effects are provided. A greater understanding of the role of pain modulation in various pain states can help characterize the manifestation and development of chronic pain and assist in predicting the response to pain-relieving treatments. Placebo and nocebo effects, intrinsic to every treatment, can be used to develop personalized therapeutic approaches that improve clinical outcomes while limiting unwanted effects.

What's in a word? How instructions, suggestions, and social information change pain and emotion

Instructions, suggestions, and other types of social information can have powerful effects on pain and emotion. Prominent examples include observational learning, social influence, placebo, and hypnosis. These different phenomena and their underlying brain mechanisms have been studied in partially separate literatures, which we discuss, compare, and integrate in this review. Converging findings from these literatures suggest that (1) instructions and social information affect brain systems associated with the generation of pain and emotion, and with reinforcement learning, and that (2) these changes are mediated by alterations in prefrontal systems responsible for top-down control and the generation of affective meaning. We argue that changes in expectation and appraisal, a process of assessing personal meaning and implications for wellbeing, are two potential key mediators of the effects of instructions and social information on affective experience. Finally, we propose a tentative model of how prefrontal regions, especially dorsolateral and ventromedial prefrontal cortex may regulate affective processing based on instructions and socially transmitted expectations more broadly.

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.

Critical Life Functions: Can Placebo Replace Oxygen?

A crucial question in placebo research is related to which conditions and physiological functions are affected by placebos. Here we present evidence that critical life functions, like ventilation, oxygenation, circulation, and perfusion, can be sensitive to placebo treatments in some circumstances. Indeed, we have investigated the role of placebo effects at an altitude of 3500m, where oxygen pressure is 64% compared to the sea level. In these extreme conditions, hypoxia triggers several compensatory responses, such as hyperventilation, increased cardiac output, and increased brain perfusion. A conditioned placebo procedure was found to mimic the effects of oxygen on these compensatory responses, and these effects are still present at altitudes as high as 4500 and 5500m, where oxygen pressure is only 57% and 50%, respectively, compared to the sea level. Thus, placebo effects also take place for those functions that are critical for life and whereby oxygen is the key element.

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.

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.

Neurobiological Aspects of Mindfulness in Pain Autoregulation: Unexpected Results from a Randomized-Controlled Trial and Possible Implications for Meditation Research

Background: Research has demonstrated that short meditation training may yield higher pain tolerance in acute experimental pain. Our study aimed at examining underlying mechanisms of this alleged effect. In addition, placebo research has shown that higher pain tolerance is mediated via endogenous neuromodulators: experimental inhibition of opioid receptors by naloxone antagonized this effect. We performed a trial to discern possible placebo from meditation-specific effects on pain tolerance and attention. Objectives: It was proposed that (i) meditation training will increase pain tolerance; (ii) naloxone will inhibit this effect; (iii) increased pain tolerance will correlate with improved attention performance and mindfulness. Methods: Randomized-controlled, partly blinded trial with 31 healthy meditation-naïve adults. Pain tolerance was assessed by the tourniquet test, attention performance was measured by Attention Network Test (ANT), self-perceived mindfulness by Freiburg Mindfulness Inventory. 16 participants received a 5-day meditation training, focusing on body/breath awareness; the control group (N = 15) received no intervention. Measures were taken before the intervention and on 3 consecutive days after the training, with all participants receiving either no infusion, naloxone infusion, or saline infusion (blinded). Blood samples were taken in order to determine serum morphine and morphine glucuronide levels by applying liquid chromatography-tandem mass spectrometry analysis. Results: The meditation group produced fewer errors in ANT. Paradoxically, increases in pain tolerance occurred in both groups (accentuated in control), and correlated with reported mindfulness. Naloxone showed a trend to decrease pain tolerance in both groups. Plasma analyses revealed sporadic morphine and/or morphine metabolite findings with no discernable pattern. Discussion: Main objectives could not be verified. Since underlying study goals had not been made explicit to participants, on purpose (framing effects toward a hypothesized mindfulness-pain tolerance correlation were thus avoided, trainees had not been instructed how to 'use' mindfulness, regarding pain), the question remains open whether lack of meditation effects on pain tolerance was due to these intended 'non-placebo' conditions, cultural effects, or other confounders, or on an unsuitable paradigm. Conclusion: Higher pain tolerance through meditation could not be confirmed.

Conditioning of amitriptyline-induced REM sleep suppression in healthy participants: A randomized controlled trial

Clinical trials in sleep disorders report substantial improvement in symptoms in their placebo groups. Behavioral conditioning is one of the underlying mechanisms of the placebo response. However, we do not know whether, and if so, the extent to which sleep architecture is influenced by behavioral conditioning, similarly to other physiological responses (i.e., those in the immune system). We therefore applied a conditioning paradigm to 39 healthy adults pairing a novel-tasting drink (conditioned stimulus, CS) with the REM sleep suppressing tricyclic antidepressant amitriptyline as unconditioned stimulus during the acquisition phase. Subsequent sole presentation of the CS (together with a placebo pill) in an evocation night led to significantly more REM sleep in the amitriptyline group. Instead of the expected REM sleep suppression in the evocation night, we observed more REM sleep, indicating a rebound that interferes with the conditioned response.

Neuro-Bio-Behavioral Mechanisms of Placebo and Nocebo Responses: Implications for Clinical Trials and Clinical Practice

The placebo effect has often been considered a nuisance in basic and particularly clinical research. This view has gradually changed in recent years due to deeper insight into the neuro-bio-behavioral mechanisms steering both the placebo and nocebo responses, the evil twin of placebo. For the neuroscientist, placebo and nocebo responses have evolved as indispensable tools to understand brain mechanisms that link cognitive and emotional factors with symptom perception as well as peripheral physiologic systems and end organ functioning. For the clinical investigator, better understanding of the mechanisms driving placebo and nocebo responses allow the control of these responses and thereby help to more precisely define the efficacy of a specific pharmacological intervention. Finally, in the clinical context, the systematic exploitation of these mechanisms will help to maximize placebo responses and minimize nocebo responses for the patient's benefit. In this review, we summarize and critically examine the neuro-bio-behavioral mechanisms underlying placebo and nocebo responses that are currently known in terms of different diseases and physiologic systems. We subsequently elaborate on the consequences of this knowledge for pharmacological treatments of patients and the implications for pharmacological research, the training of healthcare professionals, and for the health care system and future research strategies on placebo and nocebo responses.

Different Placebos, Different Mechanisms, Different Outcomes: Lessons for Clinical Trials

Clinical trials use placebos with the assumption that they are inert, thus all placebos are considered to be equal. Here we show that this assumption is wrong and that different placebo procedures are associated to different therapeutic rituals which, in turn, trigger different mechanisms and produce different therapeutic outcomes. We studied high altitude, or hypobaric hypoxia, headache, in which two different placebos were administered. The first was placebo oxygen inhaled through a mask, whereas the second was placebo aspirin swallowed with a pill. Both placebos were given after a conditioning procedure, whereby either real oxygen or real aspirin was administered for three consecutive sessions to reduce headache pain. We found that after real oxygen conditioning, placebo oxygen induced pain relief along with a reduction in ventilation, blood alkalosis and salivary prostaglandin (PG)E2, yet without any increase in blood oxygen saturation (SO2). By contrast, after real aspirin conditioning, placebo aspirin induced pain relief through the inhibition of all the products of cyclooxygenase, that is, PGD2, PGE2, PGF2, PGI2, thromboxane (TX)A2, without affecting ventilation and blood alkalosis. Therefore, two different placebos, associated to two different therapeutic rituals, used two different pathways to reduce headache pain. The analgesic effect following placebo oxygen was superior to placebo aspirin. These findings show that different placebos may use different mechanisms to reduce high altitude headache, depending on the therapeutic ritual and the route of administration. In clinical trials, placebos and outcome measures should be selected very carefully in order not to incur in wrong interpretations.

Placebo Analgesia - Understanding the Mechanisms and Implications for Clinical Practice

There are neurobiological, cognitive and conditioning processes involved in placebo mechanismsMechanisms research has demonstrated that there is not one placebo effect, but manyPlacebo effects are an inherent element in routine clinical practiceModulation of placebo mechanisms in routine practice could provide an opportunity for improving clinical care.

The neuroscience of placebo effects: connecting context, learning and health

Placebo effects are beneficial effects that are attributable to the brain-mind responses to the context in which a treatment is delivered rather than to the specific actions of the drug. They are mediated by diverse processes--including learning, expectations and social cognition--and can influence various clinical and physiological outcomes related to health. Emerging neuroscience evidence implicates multiple brain systems and neurochemical mediators, including opioids and dopamine. We present an empirical review of the brain systems that are involved in placebo effects, focusing on placebo analgesia, and a conceptual framework linking these findings to the mind-brain processes that mediate them. This framework suggests that the neuropsychological processes that mediate placebo effects may be crucial for a wide array of therapeutic approaches, including many drugs.

Placebo and nocebo effects: a complex interplay between psychological factors and neurochemical networks

Placebo and nocebo effects have recently emerged as an interesting model to understand some of the intricate underpinnings of the mind-body interaction. A variety of psychological mechanisms, such as expectation, conditioning, anxiety modulation, and reward, have been identified, and a number of neurochemical networks have been characterized across different conditions, such as pain and motor disorders. What has emerged from the recent insights into the neurobiology of placebo and nocebo effects is that the psychosocial context around the patient and the therapy, which represents the ritual of the therapeutic act, may change the biochemistry and the neuronal circuitry of the patient's brain. Furthermore, the mechanisms activated by placebos and nocebos have been found to be the same as those activated by drugs, which suggests a cognitive/affective interference with drug action. Overall, these findings highlight the important role of therapeutic rituals in the overall therapeutic outcome, including hypnosis, which may have profound implications both in routine medical practice and in the clinical trials setting.

The placebo effect in asthma

The placebo effect is a complex phenomenon occurring across a variety of clinical conditions. While much placebo research has been conducted in diseases defined by self-report such as depression, chronic pain, and irritable bowel syndrome (IBS), asthma has been proposed as a useful model because of its easily measured objective outcomes. Studies examining the placebo response in asthma have not only contributed to an understanding of the mechanisms behind the placebo response but also shed an interesting light on the current treatment and diagnosis of asthma. This paper will review current literature on placebos in general and specifically on the placebo response in asthma. It focuses on what we know about the mechanisms behind the placebo effect, whether there is a specific portion of the population who responds to placebos, which patient outcomes are influenced by the placebo effect, and whether the effect can be augmented.

The moral case for the clinical placebo

Placebos are arguably the most commonly prescribed drug, across cultures and throughout history. Nevertheless, today many would consider their use in the clinic unethical, since placebo treatment involves deception and the violation of patients' autonomy. We examine the placebo's definition and its clinical efficacy from a biopsychosocial perspective, and argue that the intentional use of the placebo and placebo effect, in certain circumstances and under several conditions, may be morally acceptable. We highlight the role of a virtue-based ethical orientation and its implications for the beneficent use of the placebo. In addition, the definitions of lying and deception are discussed, clarified and applied to the clinical placebo dilemma. Lastly, we suggest that concerns about patient autonomy, when invoked as a further argument against administering placebos, are extended beyond their reasonable and coherent application.

Placebo responses on cardiovascular, gastrointestinal, and respiratory organ functions

It is widely acknowledged that placebo responses are accompanied by physiological changes in the central nervous system, but little is known about placebo responses on end organ functions. The present chapter aims to fill this gap by reviewing the literature on peripheral placebo responses. Overall, there is a wide range of placebo and nocebo responses on various organ functions of the cardiovascular, the gastrointestinal system, and the respiratory system. Most of these studies used expectation paradigms to elicit placebo and nocebo responses. Expectations can affect heart rate, blood pressure, coronary diameter, gastric motility, bowel motility, and lung function. Classical conditioning can induce placebo respiratory depression after prior exposure to opioid drugs, and habitual coffee drinkers show physiological arousal in response to coffee-associated stimuli. Similar to findings in placebo pain research, peripheral placebo responses can be target specific. The autonomic nervous system is a likely candidate to mediate peripheral placebo responses. Further studies are necessary to identify the brain mechanisms and pathways involved in peripheral placebo responses.

Placebo, nocebo, and learning mechanisms

Recent substantial laboratory and theoretical research hints for different learning mechanisms regulating the formation of placebo and nocebo responses. Moreover, psychological and biological variants may play a role as modulators of learning mechanisms underlying placebo and nocebo responses. In this chapter, we present pioneering and recent human and nonhuman research that has impressively increased our knowledge of learning mechanisms in the context of placebo and nocebo effects across different physiological processes and pathological conditions.

Mechanisms of the placebo response in pain in osteoarthritis

INTRODUCTION

Administration of a placebo associates with symptomatic improvement in many conditions--the so-called placebo response. In this review we explain the concept of placebo response, examine the data that supports existence in osteoarthritis (OA), and discuss its possible mechanisms and determinants.

METHODS

A Pubmed literature search was carried out. Key articles were identified, and their findings discussed in a narrative review.

RESULTS

Pain, stiffness, self-reported function and physician-global assessment in OA clearly improve in response to placebo. However, more objective measures such as quadriceps strength and radiographic progression appear less responsive. Although not directly studied in OA, contextual effects, patient expectation and conditioning are believed to be the main mechanisms. Neurotransmitter changes that mediate placebo-induced analgesia include increased endogenous opioid levels, increased dopamine levels, and reduced levels of cholecystokinin. Almost all parts of the brain involved in pain processing are influenced during placebo-induced analgesia. Determinants of the magnitude of placebo response include the patient-practitioner interaction, treatment response expectancy, knowledge of being treated, patient personality traits and placebo specific factors such as the route and frequency of administration, branding, and treatment costs.

CONCLUSION

Clearer understanding of the neurobiology of placebo response validates its existence as a real phenomenon. Although routine administration of placebo for symptomatic improvement is difficult to justify, contextual factors that enhance treatment response should be employed in the management of chronic painful conditions such as OA where available treatments have only modest efficacy.

Placebo and the new physiology of the doctor-patient relationship

Modern medicine has progressed in parallel with the advancement of biochemistry, anatomy, and physiology. By using the tools of modern medicine, the physician today can treat and prevent a number of diseases through pharmacology, genetics, and physical interventions. Besides this materia medica, the patient's mind, cognitions, and emotions play a central part as well in any therapeutic outcome, as investigated by disciplines such as psychoneuroendocrinoimmunology. This review describes recent findings that give scientific evidence to the old tenet that patients must be both cured and cared for. In fact, we are today in a good position to investigate complex psychological factors, like placebo effects and the doctor-patient relationship, by using a physiological and neuroscientific approach. These intricate psychological factors can be approached through biochemistry, anatomy, and physiology, thus eliminating the old dichotomy between biology and psychology. This is both a biomedical and a philosophical enterprise that is changing the way we approach and interpret medicine and human biology. In the first case, curing the disease only is not sufficient, and care of the patient is of tantamount importance. In the second case, the philosophical debate about the mind-body interaction can find some important answers in the study of placebo effects. Therefore, maybe paradoxically, the placebo effect and the doctor-patient relationship can be approached by using the same biochemical, cellular and physiological tools of the materia medica, which represents an epochal transition from general concepts such as suggestibility and power of mind to a true physiology of the doctor-patient interaction.

Handling Ibuprofen increases pain tolerance and decreases perceived pain intensity in a cold pressor test

Pain contributes to health care costs, missed work and school, and lower quality of life. Extant research on psychological interventions for pain has focused primarily on developing skills that individuals can apply to manage their pain. Rather than examining internal factors that influence pain tolerance (e.g., pain management skills), the current work examines factors external to an individual that can increase pain tolerance. Specifically, the current study examined the nonconscious influence of exposure to meaningful objects on the perception of pain. Participants (N = 54) completed a cold pressor test, examined either ibuprofen or a control object, then completed another cold pressor test. In the second test, participants who previously examined ibuprofen reported experiencing less intense pain and tolerated immersion longer (relative to baseline) than those who examined the control object. Theoretical and applied implications of these findings are discussed.

Placebo effect model in asthma clinical studies: longitudinal meta-analysis of forced expiratory volume in 1 second

OBJECTIVE

Our objective was to describe the time course of the placebo effect in asthma and quantitatively investigate the affective factors of the placebo effect for the placebo response simulation during the asthma clinical study design.

METHODS

We conducted a systemic search of public data sources for the study-level forced expiratory volume in 1 second (FEV(1)) to build the placebo effect model for studies by oral or inhaled administrations simultaneously. The administration routes, types of inhalation device, mean patient age, mean male proportion, baseline FEV(1), disease severity, year of publication, inhaled corticosteroid status during the treatment, and dropout rate were tested as covariates.

RESULTS

There are 34 literature sources containing 178 mean values for FEV(1) presenting the individual observations from about 3,703 patients. The exponential models adequately described the time course of placebo effect with the typical value of the maximum placebo effect (P(max)) of 0.060 L. Dropout rate incorporated in the residual error model and the disease severity (mild to moderate and moderate to severe) at baseline were covariates that remained in the final model.

CONCLUSIONS

The placebo effect is adequately described by an exponential model over time. By incorporating the dropout rate in the residual error model, the estimation precision was improved. The model could predict the placebo response profile in mild to severe asthmatic patients for the asthma clinical study design and could also be a structure model of the placebo effect for the pure drug effect evaluation in the asthma clinical trials.

Placebo mechanisms across different conditions: from the clinical setting to physical performance

Although the great increase in interest in the placebo phenomenon was spurred by the clinical implications of its use, the progressive elucidation of the neurobiological and pharmacological mechanisms underlying the placebo effect also helps cast new light on the relationship between mind (and brain) and body, a topic of foremost philosophical importance but also a major medical issue in light of the complex interactions between the brain on the one hand and body functions on the other. While the concept of placebo can be a general one, with a broad definition generally applicable to many different contexts, the description of the cerebral processes called into action in specific situations can vary widely. In this paper, examples will be given where physiological or pathological conditions are altered following the administration of an inert substance or verbal instructions tailored to induce expectation of a change, and explanations will be offered with details on neurotransmitter changes and neural pathways activated. As an instance of how placebo effects can extend beyond the clinical setting, data in the physical performance domain and implications for sport competitions will also be presented and discussed.

Implicit versus explicit associative learning and experimentally induced placebo hypoalgesia

The present study examined whether 1) placebo hypoalgesia can be generated through implicit associative learning (ie, conditioning in the absence of conscious awareness) and 2) the magnitude of placebo hypoalgesia changes when expectations about pain are made explicit. The temperature of heat pain stimuli was surreptitiously lowered during conditioning trials for the placebo cream and the magnitude of the placebo effect was assessed during a subsequent set of trials when the temperature was the same for both placebo and control conditions. To assess whether placebo hypoalgesia could be generated from an implicit tactile stimulus, a 2 × 2 design was used with direction of cream application as one factor and verbal information about which cream was being applied as the second factor. A significant placebo effect was observed when participants received verbal information about which cream was being applied but not following implicit conditioning alone. However, 87.5% of those who showed a placebo response as the result of implicit conditioning were able to accurately guess the order of cream application during the final trial, despite a lack of awareness about the sensory manipulation and low confidence in their ratings, suggesting implicit learning in some participants. In summary, implicit associative learning was evident in some participants but it was not sufficient to produce a placebo effect suggesting some level of explicit expectation or cognitive mediation may be necessary. Notably, the placebo response was abolished when expectations were made explicit, suggesting a delicate interplay between attention and expectation.

Placebo analgesia, acupuncture and sham surgery

Invasive procedures, such as surgery and acupuncture, are likely better than the others in terms of eliciting placebo analgesia. Understanding how invasive procedures can elicit enhanced placebo responses may provide new insights into mechanisms underlying placebo analgesia. In this essay, it is argued that sensory, cognitive and emotional factors are major determinants of the magnitude of placebo analgesia. Sham surgery and acupuncture are good examples of placebo interventions, which generate robust placebo responses through simultaneously manipulating such three factors.

A prefrontal non-opioid mechanism in placebo analgesia

Behavioral studies have suggested that placebo analgesia is partly mediated by the endogenous opioid system. Expanding on these results we have shown that the opioid-receptor-rich rostral anterior cingulate cortex (rACC) is activated in both placebo and opioid analgesia. However, there are also differences between the two treatments. While opioids have direct pharmacological effects, acting on the descending pain inhibitory system, placebo analgesia depends on neocortical top-down mechanisms. An important difference may be that expectations are met to a lesser extent in placebo treatment as compared with a specific treatment, yielding a larger error signal. As these processes previously have been shown to influence other types of perceptual experiences, we hypothesized that they also may drive placebo analgesia. Imaging studies suggest that lateral orbitofrontal cortex (lObfc) and ventrolateral prefrontal cortex (vlPFC) are involved in processing expectation and error signals. We re-analyzed two independent functional imaging experiments related to placebo analgesia and emotional placebo to probe for a differential processing in these regions during placebo treatment vs. opioid treatment and to test if this activity is associated with the placebo response. In the first dataset lObfc and vlPFC showed an enhanced activation in placebo analgesia vs. opioid analgesia. Furthermore, the rACC activity co-varied with the prefrontal regions in the placebo condition specifically. A similar correlation between rACC and vlPFC was reproduced in another dataset involving emotional placebo and correlated with the degree of the placebo effect. Our results thus support that placebo is different from specific treatment with a prefrontal top-down influence on rACC.

The silent healer: the role of communication in placebo effects

Placebo effects have an ambiguous reputation, as they are associated with sham treatment and deceit on the one hand and as interesting phenomena, which might be clinically relevant on the other. The goal of this paper is to demonstrate that placebo effects are relevant and can be used as an effective part of many treatments by using communication targeting placebo effect mechanisms. We examined the history of placebos and the placebo effect, addressing common misconceptions and disentangling ambiguities. We then reviewed whether the placebo effect can be robustly shown in the current literature, and zoomed in on the plausible mechanisms (conditioning, expectancies and affect manipulation) through which the placebo effect might be produced. Observing the link with the doctor-patient communication literature, and pleading for a better integration of the two research traditions we conclude by setting out a research agenda for testing the role of communication in placebo effects.

The placebo effect and homeopathy

BACKGROUND

Like other forms of medicine, including Complementary and Alternative Medicine (CAM), homeopathy elicits expectations in patients. The physician-patient relationship, personal and comprehensive treatment and lack of adverse effects are elements in creating positive expectations. Other elements may be associated with negative expectations.

METHODS

We conducted a systematic literature review on placebo and nocebo effects in acupuncture and homeopathy using Medline.

RESULTS

Findings on the psychophysiological and neuromediating mechanisms of the placebo-nocebo phenomenon are reviewed. Studies of these effects reveal how expectations and unconscious conditioning can be measured by imaging and EEG methods. They result in significant, non-specific therapeutic effects, which may confuse the evaluation of the specific therapeutic effects treatment, hampering selection of the simillimum.

CONCLUSIONS

Directions for future research on non-specific therapeutic effects of homeopathy to improve clinical practice and clinical research are discussed.

Biological, clinical, and ethical advances of placebo effects

For many years, placebos have been defined by their inert content and their use as controls in clinical trials and treatments in clinical practice. Recent research shows that placebo effects are genuine psychobiological events attributable to the overall therapeutic context, and that these effects can be robust in both laboratory and clinical settings. There is also evidence that placebo effects can exist in clinical practice, even if no placebo is given. Further promotion and integration of laboratory and clinical research will allow advances in the ethical use of placebo mechanisms that are inherent in routine clinical care, and encourage the use of treatments that stimulate placebo effects.

Placebo interventions for all clinical conditions

BACKGROUND

Placebo interventions are often claimed to substantially improve patient-reported and observer-reported outcomes in many clinical conditions, but most reports on effects of placebos are based on studies that have not randomised patients to placebo or no treatment. Two previous versions of this review from 2001 and 2004 found that placebo interventions in general did not have clinically important effects, but that there were possible beneficial effects on patient-reported outcomes, especially pain. Since then several relevant trials have been published.

OBJECTIVES

Our primary aims were to assess the effect of placebo interventions in general across all clinical conditions, and to investigate the effects of placebo interventions on specific clinical conditions. Our secondary aims were to assess whether the effect of placebo treatments differed for patient-reported and observer-reported outcomes, and to explore other reasons for variations in effect.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library Issue 4, 2007), MEDLINE (1966 to March 2008), EMBASE (1980 to March 2008), PsycINFO (1887 to March 2008) and Biological Abstracts (1986 to March 2008). We contacted experts on placebo research, and read references in the included trials.

SELECTION CRITERIA

We included randomised placebo trials with a no-treatment control group investigating any health problem.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. We contacted study authors for additional information. Trials with binary data were summarised using relative risk (a value of less than 1 indicates a beneficial effect of placebo), and trials with continuous outcomes were summarised using standardised mean difference (a negative value indicates a beneficial effect of placebo).

MAIN RESULTS

Outcome data were available in 202 out of 234 included trials, investigating 60 clinical conditions. We regarded the risk of bias as low in only 16 trials (8%), five of which had binary outcomes.In 44 studies with binary outcomes (6041 patients), there was moderate heterogeneity (P < 0.001; I(2) 45%) but no clear difference in effects between small and large trials (symmetrical funnel plot). The overall pooled effect of placebo was a relative risk of 0.93 (95% confidence interval (CI) 0.88 to 0.99). The pooled relative risk for patient-reported outcomes was 0.93 (95% CI 0.86 to 1.00) and for observer-reported outcomes 0.93 (95% CI 0.85 to 1.02). We found no statistically significant effect of placebo interventions in four clinical conditions that had been investigated in three trials or more: pain, nausea, smoking, and depression, but confidence intervals were wide. The effect on pain varied considerably, even among trials with low risk of bias.In 158 trials with continuous outcomes (10,525 patients), there was moderate heterogeneity (P < 0.001; I(2) 42%), and considerable variation in effects between small and large trials (asymmetrical funnel plot). It is therefore a questionable procedure to pool all the trials, and we did so mainly as a basis for exploring causes for heterogeneity. We found an overall effect of placebo treatments, standardised mean difference (SMD) -0.23 (95% CI -0.28 to -0.17). The SMD for patient-reported outcomes was -0.26 (95% CI -0.32 to -0.19), and for observer-reported outcomes, SMD -0.13 (95% CI -0.24 to -0.02). We found an effect on pain, SMD -0.28 (95% CI -0.36 to -0.19)); nausea, SMD -0.25 (-0.46 to -0.04)), asthma (-0.35 (-0.70 to -0.01)), and phobia (SMD -0.63 (95% CI -1.17 to -0.08)). The effect on pain was very variable, also among trials with low risk of bias. Four similarly-designed acupuncture trials conducted by an overlapping group of authors reported large effects (SMD -0.68 (-0.85 to -0.50)) whereas three other pain trials reported low or no effect (SMD -0.13 (-0.28 to 0.03)). The pooled effect on nausea was small, but consistent. The effects on phobia and asthma were very uncertain due to high risk of bias. There was no statistically significant effect of placebo interventions in the seven other clinical conditions investigated in three trials or more: smoking, dementia, depression, obesity, hypertension, insomnia and anxiety, but confidence intervals were wide.Meta-regression analyses showed that larger effects of placebo interventions were associated with physical placebo interventions (e.g. sham acupuncture), patient-involved outcomes (patient-reported outcomes and observer-reported outcomes involving patient cooperation), small trials, and trials with the explicit purpose of studying placebo. Larger effects of placebo were also found in trials that did not inform patients about the possible placebo intervention.

AUTHORS' CONCLUSIONS

We did not find that placebo interventions have important clinical effects in general. However, in certain settings placebo interventions can influence patient-reported outcomes, especially pain and nausea, though it is difficult to distinguish patient-reported effects of placebo from biased reporting. The effect on pain varied, even among trials with low risk of bias, from negligible to clinically important. Variations in the effect of placebo were partly explained by variations in how trials were conducted and how patients were informed.

Would the elderly be better off if they were given more placebos?

Placebos are useful in the medical care of the elderly, although the exact definition of a "placebo" or "placebo effect" is difficult to define precisely. They have an important role as control treatments in research trials, but a non-specific "placebo effect" may also be beneficial part of many physician-patient interactions. Physicians also give them deliberately according to several studies worldwide to satisfy patient demands or because they believe in a "placebo effect" among other reasons. A significant placebo effect has been observed among older patients in clinical trials of antidepressants (12-15%), and in treatments of Parkinson's disease (16%). Placebos activate serotonergic pathways in the brain used by antidepressants. In Parkinson's disease, the administration of a placebo stimulates dopamine release in the dorsal (resulting in motor effects) and ventral striatum (which influences expectation of reward). Much of our understanding of the placebo effect comes from studies of placebo analgesia which is influenced by conditioning, expectation, meaning and context of the treatment for the patient, and patient-physician interaction. It is anatomically medicated by brain opioid pathways. Response to "sham" acupuncture in osteoarthritis may be an example of its use in the elderly. Placebos have often been considered a deception and thus unethical. On the other hand, some physicians and ethicists have suggested conditions for appropriate uses for placebos. A placebo might offer the theoretical advantage of an inexpensive treatment that would not cause adverse drug reactions or interactions with other medications, potentially avoiding complications of polypharmacy.

The rebirth of neuroscience in psychosomatic medicine, Part II: clinical applications and implications for research

During the second half of the last century, biopsychosocial research in psychosomatic medicine largely ignored the brain. Neuroscience has started to make a comeback in psychosomatic medicine research and promises to advance the field in important ways. In this paper we briefly review select brain imaging research findings in psychosomatic medicine in four key areas: cardiovascular regulation, visceral pain in the context of functional gastrointestinal disorders, acute and chronic somatic pain and placebo. In each area, there is a growing literature that is beginning to define a network of brain areas that participate in the functions in question. Evidence to date suggests that cortical and subcortical areas that are involved in emotion and emotion regulation play an important role in each domain. Neuroscientific research is therefore validating findings from previous psychosomatic research and has the potential to extend knowledge by delineating the biological mechanisms that link mind and body more completely and with greater specificity. We conclude with a discussion of the implications of this work for how research in psychosomatic medicine is conducted, the ways in which neuroscientific advances can lead to new clinical applications in psychosomatic contexts, the implications of this work for the field of medicine more generally, and the priorities for research in the next 5 to 10 years.

A phenomenology of the 'placebo effect': taking meaning from the mind to the body

Most mainstream attempts to understand the "placebo effect" invoke expectancy theory, arguing that expecting certain outcomes from a treatment or intervention can manifest those outcomes. Expectancy theory is incompatible with the phenomena of placebo responses, more appropriately named "meaning responses." The expectancy account utilizes reflexive consciousness to connect a world of conceptual representations to mechanical physiology. An alternative account based upon Merleau-Ponty's motor intentionality argues that the body understands and is capable of responding to meanings without the need for any conceptual or linguistic content. A motor intentional framework of meaning poses dramatic implications for the interpretation of clinical trials and in the clinical practice of medicine. Most strongly, it argues that the empathic physician can facilitate the physiologic effects of treatments through skillful participation and manipulation of the meaning response.

A comprehensive review of the placebo effect: recent advances and current thought

Our understanding and conceptualization of the placebo effect has shifted in emphasis from a focus on the inert content of a physical placebo agent to the overall simulation of a therapeutic intervention. Research has identified many types of placebo responses driven by different mechanisms depending on the particular context wherein the placebo is given. Some placebo responses, such as analgesia, are initiated and maintained by expectations of symptom change and changes in motivation/emotions. Placebo factors have neurobiological underpinnings and actual effects on the brain and body. They are not just response biases. Other placebo responses result from less conscious processes, such as classical conditioning in the case of immune, hormonal, and respiratory functions. The demonstration of the involvement of placebo mechanisms in clinical trials and routine clinical practice has highlighted interesting considerations for clinical trial design and opened up opportunities for ethical enhancement of these mechanisms in clinical practice.