A signal detection theory analysis of the placebo effect

Uncertainty of treatment efficacy moderates placebo effects on reinforcement learning

The placebo-reward hypothesis postulates that positive effects of treatment expectations on health (i.e., placebo effects) and reward processing share common neural underpinnings. Moreover, experiments in humans and animals indicate that reward uncertainty increases striatal dopamine, which is presumably involved in placebo responses and reward learning. Therefore, treatment uncertainty analogously to reward uncertainty may affect updating from rewards after placebo treatment. Here, we address whether different degrees of uncertainty regarding the efficacy of a sham treatment affect reward sensitivity. In an online between-subjects experiment with N = 141 participants, we systematically varied the provided efficacy instructions before participants first received a sham treatment that consisted of listening to binaural beats and then performed a probabilistic reinforcement learning task. We fitted a Q-learning model including two different learning rates for positive (gain) and negative (loss) reward prediction errors and an inverse gain parameter to behavioral decision data in the reinforcement learning task. Our results yielded an inverted-U-relationship between provided treatment efficacy probability and learning rates for gain, such that higher levels of treatment uncertainty, rather than of expected net efficacy, affect presumably dopamine-related reward learning. These findings support the placebo-reward hypothesis and suggest harnessing uncertainty in placebo treatment for recovering reward learning capabilities.

Efficacy and safety of transcranial pulse stimulation in young adolescents with attention-deficit/hyperactivity disorder: a pilot, randomized, double-blind, sham-controlled trial

Background

This is the first study to evaluate the efficacy and safety of transcranial pulse stimulation (TPS) for the treatment of attention-deficit/hyperactivity disorder (ADHD) among young adolescents in Hong Kong.

Methods

This double-blind, randomized, sham-controlled trial included a TPS group and a sham TPS group, encompassing a total of 30 subjects aged 12-17 years who were diagnosed with ADHD. Baseline measurements SNAP-IV, ADHD RS-IV, CGI and executive functions (Stroop tests, Digit Span) and post-TPS evaluation were collected. Both groups were assessed at baseline, immediately after intervention, and at 1-month and 3-month follow-ups. Repeated-measures ANOVAs were used to analyze data.

Results

The TPS group exhibited a 30% reduction in the mean SNAP-IV score at postintervention that was maintained at 1- and 3-month follow-ups.

Conclusion

TPS is an effective and safe adjunct treatment for the clinical management of ADHD.

Clinical trial registration

ClinicalTrials.Gov, identifier NCT05422274.

Placebo Effects Are Small on Average in the 7.5% CO2 Inhalational Model of Generalized Anxiety

BACKGROUND

Anxiety disorders are highly prevalent and socio-economically costly. Novel pharmacological treatments for these disorders are needed because many patients do not respond to current agents or experience unwanted side effects. However, a barrier to treatment development is the variable and large placebo response rate seen in trials of novel anxiolytics. Despite this, the mechanisms that drive placebo responses in anxiety disorders have been little investigated, possibly due to low availability of convenient experimental paradigms. We aimed to develop and test a novel protocol for inducing placebo anxiolysis in the 7.5% CO2 inhalational model of generalized anxiety in healthy volunteers.

METHODS

Following a baseline 20-minute CO2 challenge, 32 healthy volunteers were administered a placebo intranasal spray labelled as either the anxiolytic "lorazepam" or "saline." Following this, participants surreptitiously underwent a 20-minute inhalation of normal air. Post-conditioning, a second dose of the placebo was administered, after which participants completed another CO2 challenge.

RESULTS

Participants administered sham "lorazepam" reported significant positive expectations of reduced anxiety (P = .001), but there was no group-level placebo effect on anxiety following CO2 challenge post-conditioning (Ps > .350). Surprisingly, we found many participants exhibited unexpected worsening of anxiety, despite positive expectations.

CONCLUSIONS

Contrary to our hypothesis, our novel paradigm did not induce a placebo response, on average. It is possible that effects of 7.5% CO2 inhalation on prefrontal cortex function or behavior in line with a Bayesian predictive coding framework attenuated the effect of expectations on subsequent placebo response. Future studies are needed to explore these possibilities.

Yoga and massage are associated with small experimental placebo effects in chronic orofacial pain

BACKGROUND

Complementary and Integrative Health Approaches (CIHA), including but not limited to, natural products and Mind and Body Practices (MBPs), are promising non-pharmacological adjuvants to the arsenal of pain management therapeutics. We aim to establish possible relationships between use of CIHA and the capacity of descending pain modulatory system in the form of occurrence and magnitude of placebo effects in a laboratory setting.

METHODS

This cross-sectional study investigated the relationship between self-reported use of CIHA, pain disability, and experimentally induced placebo hypoalgesia in chronic pain participants suffering from Temporomandibular Disorders (TMD). In the 361 enrolled TMD participants, placebo hypoalgesia was measured using a well-established paradigm with verbal suggestions and conditioning cues paired with distinct heat painful stimulations. Pain disability was measured with the Graded Chronic Pain Scale, and use of CIHA were recorded with a checklist as part of the medical history.

RESULTS

Use of physically oriented MBPs (e.g., yoga and massage) was associated with reduced placebo effects (F1,2110.44  = 23.15, p < 0.001, Cohen's d = 0.171). Further, linear regressions indicated that greater number of physically oriented MBPs predicted smaller placebo effects (β = -0.17, p = 0.002), and less likelihood of being a placebo responder (OR = 0.70, p = 0.004). Use of psychologically oriented MBPs and natural product were not associated with placebo effects magnitude and responsiveness.

CONCLUSIONS

Our findings suggest that use of physically oriented CIHA was associated with experimental placebo effects possibly through an optimized capability to recognize distinct somatosensorial stimulations. Future research is needed to understand the mechanisms underlying placebo-induced pain modulation in CIHA users.

SIGNIFICANCE

Chronic pain participants who use physically oriented mind-body practices, such as yoga and massage, demonstrated attenuated experimentally induced placebo hypoalgesia in comparison with those who do not use them. This finding disentangled the relationship between use of complementary and integrative approaches and placebo effects, providing the potential therapeutic perspective of endogenous pain modulation in chronic pain management.

Multiple Criterion and Multiple Stimulus Signal Detection Theory Analysis of Corneal Painful and Cool Pneumatic Stimuli

Purpose: To evaluate the detectability of pneumatic corneal stimuli and response bias using multi-stimuli multi-criterion signal detection theory (MSDT).

Methods: Thirty-six participants were recruited using convenience sampling. A Waterloo Belmonte esthesiometer was used to deliver cold, mechanical, and chemical stimuli to the center of the cornea at three separate study visits. The stimulus type was assigned randomly to each visit at the start of the study. The threshold (baseline for detection theory experiment) for the assigned stimulus type was obtained using the ascending method of limits. In the cold and mechanical MSDT experiments, 100 trials (80 signal (20 each for 4 intensities) and 20 catch trials) were presented in randomized order, and participants responded with a 5-point confidence rating to each trial. In the chemical MSDT experiments, 50 trials (20 signal trials each for two intensities and 10 catch trials) were presented, and responses were provided using 4-point confidence ratings. Detection theory indices were calculated individually and as groups, which were then analyzed using mixed models and paired t-tests.

Results: Detectability (d_a) and the area under the curve (A_z) were significantly different between stimulus intensities within each stimulus type (all p < 0.001) but were not different between the stimulus types. Receiver operating characteristics (ROC) curves were separable between the scaled intensities for all stimulus types, and no overlaps were observed in the z-ROC space. The log-likelihood ratio (lnβ) depended on stimulus intensity and psychophysical criterion for all stimulus types.

Conclusion: It is feasible to use MSDT for analyzing ocular surface sensory processing and the theory provides insight into the possible bias associated with the use of pneumatic stimuli. With noxious and non-noxious pneumatic stimulation, detectability and criteria vary systematically with stimulus intensity, a result that cannot be derived using classical psychophysics and this highlights the importance of signal detection theory and its approaches in studying ocular surface pain and thermal processing.

The role of superstition in the placebo effect on memory performance

Superstitions and the placebo effect have each been found to influence human behaviour. The present study aimed to determine whether there is a relationship between superstition and the placebo effect, and whether this relationship affects human cognition and behaviour. We hypothesized that more superstitious people would be more prone to the placebo effect and that it would improve their performance on cognitive tasks. Results showed that in the placebo condition, more superstitious people memorized more words than less superstitious people. However, in the control condition, less superstitious people memorized more words than more superstitious people. Overall, the findings supported our hypothesis. The findings of the study are important, as they draw a link between the placebo effect and superstition, and further show that these two elements impact human performance in cognitive ability tasks.

Detectability and Bias Indices of Pneumatic Corneal Stimuli Using Signal Detection Theory

Purpose

To evaluate the feasibility of using signal detection theory (SDT) in estimating criterion and detectability indices for corneal pneumatic stimuli and test corneal psychophysical data against linking hypotheses from nonprimate physiology using Bayesian analysis.

Methods

Corneal pneumatic stimuli were delivered using the Waterloo Belmonte esthesiometer. Corneal thresholds were estimated in 30 asymptomatic participants and 1.5× threshold stimuli were used as signals (with 0.4 probability). There were 100-trial mechanical and cold stimulus experiments and 50-trial chemical experiments. Trials were demarcated auditorily and "yes" or "no" recorded after each trial. Cold stimulus experiments were conducted with 0.6 signal probability. Criterion (c), likelihood ratio (lnβ), and d' were calculated from the yes-no responses.

Results

Average d' was 0.59 ± 0.1, 1.65 ± 0.37, and 1.14 ± 0.3 units for cold, mechanical, and chemical stimuli, respectively. Bayes factors obtained using Bayesian analysis of variance mildly favored (BF10 = 1.55) differences between d's of the stimulus types, with no support for differences in criteria between stimulus types. Multiple comparisons of d' supported linking hypotheses based on nociception and nerve conductance theories.

Conclusions

Our experiments are the first to demonstrate the feasibility of estimating SDT indices and test different hypotheses. The conservative strategy (reporting "no" more often) chosen by participants was anticipated due to relatively large proportion of catch trials.

Translational Relevance

SDT when using pneumatic esthesiometry is vital to evaluate bias in responses of participants. Considering the varied forms of inherent noise in the corneal sensory system, SDT is critical to understand the sensory and decisional characteristics.

The placebo and its effects: A psychoneuroendocrinological perspective

Placebos are usually employed deceptively in clinical trials in order to control for non-specific effects. However, since placebos themselves have been found to cause clinically relevant changes and in some cases are indistinguishable from the verum they are tested against, this theoretically inert, but practically effective intervention has become a scientific discipline in its own right. In this review, it is argued that placebos are generic and genuine biopsychosocial interventions and as such are highly interesting candidates for a psychoneuroendocrinological perspective. Yet, despite a considerable conceptual proximity between explanatory models of placebos and their effects with psychoneuroendocrine models and findings, placebos have thus far not been subject to systematic psychoneuroendocrine examination. Consequently, it would be highly interesting and informative to make placebos the target of psychoneuroendocrine scrutiny.

Is placebo analgesia for heat pain a sensory effect? An exploratory study on minimizing the influence of response bias

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We explored whether placebo analgesia alters afferent nociceptive processing.

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Healthy adult participants received a standard heat placebo induction procedure.

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Placebo manipulation was modified to reduce experimenter demand.

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A novel inter-arm sensory discrimination task was administered.

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Only placebo responders showed changes in discriminative ability.

We explored the ongoing question of whether placebo analgesia alters afferent nociceptive processing in a novel paradigm designed to minimize the role of response bias in placebo measurement. First, healthy adult participants received a standard heat placebo induction and conditioning procedure using a topical “analgesic” cream applied to one arm. During a subsequent placebo testing procedure, participants rated stimuli on the placebo-treated arm and untreated arm, using a task that minimized subjects’ ability to guess the expected response, thus reducing experimenter demand. Retrospectively participants reported moderate analgesia effectiveness (mean = 5.3/10), but for individual temperature ratings, only 2 subjects exhibited a perceptual placebo response >5 points. Next, these subjects completed a novel, exploratory task designed to measure changes in inter-arm in discriminative accuracy that would be expected from changes in afferent nociception. Both placebo responders (but no non-responders) showed reduced discriminative ability when the hotter stimulus occurred on the placebo arm, an effect consistent with alterations in nociceptive afferent flow and unlikely to be caused by response bias.

Rethinking the treatment of chronic fatigue syndrome-a reanalysis and evaluation of findings from a recent major trial of graded exercise and CBT

BACKGROUND

The PACE trial was a well-powered randomised trial designed to examine the efficacy of graded exercise therapy (GET) and cognitive behavioural therapy (CBT) for chronic fatigue syndrome. Reports concluded that both treatments were moderately effective, each leading to recovery in over a fifth of patients. However, the reported analyses did not consistently follow the procedures set out in the published protocol, and it is unclear whether the conclusions are fully justified by the evidence.

METHODS

Here, we present results based on the original protocol-specified procedures. Data from a recent Freedom of Information request enabled us to closely approximate these procedures. We also evaluate the conclusions from the trial as a whole.

RESULTS

On the original protocol-specified primary outcome measure - overall improvement rates - there was a significant effect of treatment group. However, the groups receiving CBT or GET did not significantly outperform the Control group after correcting for the number of comparisons specified in the trial protocol. Also, rates of recovery were consistently low and not significantly different across treatment groups. Finally, on secondary measures, significant effects were almost entirely confined to self-report measures. These effects did not endure beyond two years.

CONCLUSIONS

These findings raise serious concerns about the robustness of the claims made about the efficacy of CBT and GET. The modest treatment effects obtained on self-report measures in the PACE trial do not exceed what could be reasonably accounted for by participant reporting biases.

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.

How empathic is your healthcare practitioner? A systematic review and meta-analysis of patient surveys

BACKGROUND

A growing body of evidence suggests that healthcare practitioners who enhance how they express empathy can improve patient health, and reduce medico-legal risk. However we do not know how consistently healthcare practitioners express adequate empathy. In this study, we addressed this gap by investigating patient rankings of practitioner empathy.

METHODS

We conducted a systematic review and meta-analysis of studies that asked patients to rate their practitioners' empathy using the Consultation and Relational Empathy (CARE) measure. CARE is emerging as the most common and best-validated patient rating of practitioner empathy. We searched: MEDLINE, Embase, PsycINFO, Cinahl, Science & Social Science Citation Indexes, the Cochrane Library and PubMed from database inception to March 2016. We excluded studies that did not use the CARE measure. Two reviewers independently screened titles and extracted data on average CARE scores, demographic data for patients and practitioners, and type of healthcare practitioners.

RESULTS

Sixty-four independent studies within 51 publications had sufficient data to pool. The average CARE score was 40.48 (95% CI, 39.24 to 41.72). This rank s in the bottom 5th percentile in comparison with scores collected by CARE developers. Longer consultations (n = 13) scored 15% higher (42.60, 95% CI 40.66 to 44.54) than shorter (n = 9) consultations (34.93, 95% CI 32.63 to 37.24). Studies with mostly (>50%) female practitioners (n = 6) showed 16% higher empathy scores (42.77, 95% CI 38.98 to 46.56) than those with mostly (>50%) male (n = 6) practitioners (34.84, 95% CI 30.98 to 38.71). There were statistically significant (P = 0.032) differences between types of providers (allied health professionals, medical students, physicians, and traditional Chinese doctors). Allied Health Professionals (n = 6) scored the highest (45.29, 95% CI 41.38 to 49.20), and physicians (n = 39) scored the lowest (39.68, 95% CI 38.29 to 41.08). Patients in Australia, the USA, and the UK reported highest empathy ratings (>43 average CARE), with lowest scores (<35 average CARE scores) in Hong Kong.

CONCLUSIONS

Patient rankings of practitioner empathy are highly variable, with female practitioners expressing empathy to patients more effectively than male practitioners. The high variability of patient rating of practitioner empathy is likely to be associated with variable patient health outcomes. Limitations included frequent failure to report response rates introducing a risk of response bias. Future work is warranted to investigate ways to reduce the variability in practitioner empathy.

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.

The effect of patient-practitioner communication on pain: a systematic review

BACKGROUND AND OBJECTIVE

Communication between patients and health care practitioners is expected to benefit health outcomes. The objective of this review was to assess the effects of experimentally varied communication on clinical patients' pain.

DATABASES AND DATA TREATMENT

We searched in July 2012, 11 databases supplemented with forward and backward searches for (quasi-) randomized controlled trials in which face-to-face communication was manipulated. We updated in June 2015 using the four most relevant databases (CINAHL, Cochrane Central, Psychinfo, PubMed).

RESULTS

Fifty-one studies covering 5079 patients were included. The interventions were separated into three categories: cognitive care, emotional care, procedural preparation. In all but five studies the outcome concerned acute pain. We found that, in general, communication has a small effect on (acute) pain. The 19 cognitive care studies showed that a positive suggestion may reduce pain, whereas a negative suggestion may increase pain, but effects are small. The 14 emotional care studies showed no evidence of a direct effect on pain, although four studies showed a tendency for emotional care lowering patients' pain. Some of the 23 procedural preparation interventions showed a weak to moderate effect on lowering pain.

CONCLUSIONS

Different types of communication have a significant but small effect on (acute) pain. Positive suggestions and informational preparation seem to lower patients' pain. Communication interventions show a large variety in quality, complexity and methodological rigour; they often used multiple components and it remains unclear what the effective elements of communication are. Future research is warranted to identify the effective components.

THE EFFECT OF LOW POWER GLASSES AT CLOSE DISTANCES ON VISUAL PERFORMANCE

The purpose of this study was to reveal if the use of low power ophthalmic glasses (diopter values within the ± 1.00D range) in ophthalmic care may be beneficial for the treatment of low refractive vision disorders. 40 university students (10 men, 30 women), who used low power glasses at close distances (for reading on paper or on a computer screen: 40-60 centimeters approximately), voluntarily took part in this study. Ages of the participants ranged from 20 to 43 years (M = 24.9, SD = 4.4). Mean spherical refractive error was -0.38 diopters (SD = 0.49; range= -1.00-0.88). A yes/no Signal Detection procedure was used to assess whether the participants' visual sensitivity (d') or criterion of response (c) changed when they used the optical correction. There were no changes in visual sensitivity index, but significant changes in criterion of response were observed when the students used their optical correction. Changes in the criterion of response suggested the presence of a placebo effect.

A Novel Methodology to Estimate the Treatment Effect in Presence of Highly Variable Placebo Response

One of the main reasons for the inefficiency of multicenter randomized clinical trials (RCTs) in depression is the excessively high level of placebo response. The aim of this work was to propose a novel methodology to analyze RCTs based on the assumption that centers with high placebo response are less informative than the other centers for estimating the 'true' treatment effect (TE). A linear mixed-effect modeling approach for repeated measures (MMRM) was used as a reference approach. The new method for estimating TE was based on a nonlinear longitudinal modeling of clinical scores (NLMMRM). NLMMRM estimates TE by associating a weighting factor to the data collected in each center. The weight was defined by the posterior probability of detecting a clinically relevant difference between active treatment and placebo at that center. Data from five RCTs in depression were used to compare the performance of MMRM with NLMMRM. The results of the analyses showed an average improvement of ~15% in the TE estimated with NLMMRM when the center effect was included in the analyses. Opposite results were observed with MMRM: TE estimate was reduced by ~4% when the center effect was considered as covariate in the analysis. The novel NLMMRM approach provides a tool for controlling the confounding effect of high placebo response, to increase signal detection and to provide a more reliable estimate of the 'true' TE by controlling false negative results associated with excessively high placebo response.

Placebo Responses in Genetically Determined Intellectual Disability: A Meta-Analysis

Background

Genetically determined Intellectual Disability (ID) is an intractable condition that involves severe impairment of mental abilities such as learning, reasoning and predicting the future. As of today, little is known about the placebo response in patients with ID.

Objective

To determine if placebo response exists in patients with genetically determined ID.

Data sources and Study selection

We searched Medline/PubMed, EMBASE, CENTRAL and PsycINFO to find all placebo-controlled double-blind randomized clinical trials (RCTs) in patients with genetically determined ID, published up to April 2013, focusing on core ID symptoms.

Data extraction and synthesis

Two investigators extracted outcome data independently.

Main outcomes and measures

Bias-corrected standardized mean difference (Hedge’s g) was computed for each outcome measure, using the Comprehensive Meta-Analysis software. A priori defined patient sub-groups were analyzed using a mixed-effect model. The relationship between pre-defined continuous variable moderators (age, IQ, year of publication and trial duration) and effect size was analyzed using meta-regression

Results

Twenty-two placebo-controlled double-blind RCTs met the inclusion criteria (n = 721, mean age = 17.1 years, 62% men, mean trial duration = 35 weeks). There was a significant overall placebo response from pre- to post-treatment in patients with ID (g = 0.468, p = 0.002), both for “subjective outcomes” (a third-person’s evaluation of the patient) (g = 0.563, p = 0.022) and “objective outcomes” (direct evaluation of the patient’s abilities) (g = 0.434, p = 0.036). Individuals with higher IQ had higher response to placebo (p = 0.02) and no placebo response was observed in ID patients with comorbid dementia. A significant effect of age (p = 0.02) was found, indicating higher placebo responses in treatment of younger patients.

Conclusions and relevance

Results suggest that patients with genetically determined ID improve in the placebo arm of RCTs. Several mechanisms may contribute to placebo effects in ID, including expectancy, implicit learning and “placebo-by-proxy” induced by clinicians/family members. As the condition is refractory, there is little risk that improvements are explained by spontaneous remission. While new avenues for treatment of genetically determined ID are emerging, our results demonstrate how contextual factors can affect clinical outcomes and emphasize the importance of being vigilant on the role of placebos when testing novel treatments in ID.

How Is Pain Influenced by Cognition? Neuroimaging Weighs In

Neuroimaging can inform cognitive theories to the extent that particular patterns of brain activity are sensitively and specifically associated with particular types of cognitive processes. We illustrate the utility of neuroimaging data in one specific case: understanding cognitive influences on pain. We first argue that pain self-reports are often inadequate to fully characterize pain experience and the processes that underlie it. Then, we describe how neuroimaging measures have been used to corroborate the effects of psychological manipulations on pain by focusing on placebo treatments and demonstrating effects on the best available correlates of pain experience. In addition, using placebo analgesia as an example, we argue that brain evidence is useful for building psychological theories likely to yield valid and generalizable predictions, because biologically informed theories are grounded in the constraints inherent in the relevant physiological systems. Finally, we suggest that neuroimaging findings will become increasingly useful for constraining psychological inference as brain patterns diagnostic of particular types of mental events are identified and characterized. In our view, the relationships between biological findings and cognitive theory are empirically based and must develop through an iterative process of synthesis across studies, topics, and methods.

Placebo analgesia: cognition or perception

Placebo analgesia has become a well-studied phenomenon that encompasses psychology, physiology and pharmacology. In this chapter we explore the complex interactions between these disciplines in order to argue that the placebo response is more than a simple change in perception but is a cognitive style driven by prior expectations. The expectation of treatment effect is shaped by prior information and prior experience which our brain uses to predict future events. In the case of placebo analgesia the prediction of pain relief overrules the actual feeling of pain leading to a decrease in pain sensation. This altered sensation can be attributed to personality traits, altered error monitoring processes, changes in anticipatory responses to pain and activation of the endogenous opioid system. In conclusion we discuss how altered sensory processing by descending pain modulation may play a part in placebo analgesia and how the loss of the brains prefrontal regions can make it impossible to have a placebo response.

Placebo Effects and Informed Consent

The concepts of placebos and placebo effects refer to extremely diverse phenomena. I recommend dissolving the concepts of placebos and placebo effects into loosely related groups of specific mechanisms, including (potentially among others) expectation-fulfillment, classical conditioning, and attentional-somatic feedback loops. If this approach is on the right track, it has three main implications for the ethics of informed consent. First, because of the expectation-fulfillment mechanism, the process of informing cannot be considered independently from the potential effects of treatment. Obtaining informed consent influences the effects of treatment. This provides support for the authorized concealment and authorized deception paradigms, and perhaps even for outright deceptive placebo use. Second, doctors may easily fail to consider the potential benefits of conditioning, leading them to misjudge the trade-off between beneficence and autonomy. Third, how attentional-somatic feedback loops play out depends not only on the content of the informing process but also on its framing. This suggests a role for libertarian paternalism in clinical practice.

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.

Placebo analgesia affects brain correlates of error processing

Placebo analgesia (PA) is accompanied by decreased activity in pain-related brain regions, but also by greater prefrontal cortex (PFC) activation, which has been suggested to reflect increases in top-down cognitive control and regulation of pain. Here we test whether PA is associated with altered prefrontal monitoring functions that could adjust nociceptive processing to a mismatch between expected and experienced pain. We recorded event-related potentials to response errors in a go/nogo task during placebo vs. a matched control condition. Error commission was associated with two well-described components, the error-related negativity (ERN) and the error positivity (Pe). Results show that the Pe, but not the ERN, was amplified during placebo analgesia compared to the control condition, with neural sources in the lateral and medial PFC. This Pe increase was driven by participants showing a placebo-induced change in pain tolerance, but was absent in the group of non-responders. Our results shed new light on the possible functional mechanisms underlying PA, suggesting a placebo-induced transient change in prefrontal error monitoring and control functions.

The placebo effect: advances from different methodological approaches

There is accumulating evidence from different methodological approaches that the placebo effect is a neurobiological phenomenon. Behavioral, psychophysiological, and neuroimaging results have largely contributed to accepting the placebo response as real. A major aspect of recent and future advances in placebo research is to demonstrate linkages between behavior, brain, and bodily responses. This article provides an overview of the processes involved in the formation of placebo responses by combining research findings from behavioral, psychophysiological, and neuroimaging methods. The integration of these different methodological approaches is a key objective, motivating our scientific pursuits toward a placebo research that can inform and guide important future scientific knowledge.

Optimism Facilitates the Utilisation of Prior Cues

It has been shown that optimists tend to rely more on their prior expectations than sensory input when making decisions of an intense nature (Geers & Lassiter, 2002). We investigated the degree to which this tendency persists over a range of discrepancies between prior cues and actual stimuli. Eighty–seven participants were shown a subset of happy, sad and fearful pictures drawn from the Ekman facial expressions of emotion (Ekman & Oster, 1979). Each picture was preceded by a verbal cue indicating the impending emotional expression and intensity. The displayed pictures were either in agreement, slightly discrepant or very discrepant with the cue. Participants rated the extent to which they agreed/disagreed with the expectation cue. Probit signal detection models were used to produce acquiescence for each subject at each level of discrepancy. Correlation analysis was performed on acquiescence and dispositional optimism scores. There was a significant correlation between all acquiescence scores for levels of discrepancies and dispositional optimism. Optimism appears to be a trait associated with acquiescence. The apparent tendency of optimists to comply may be due to a cognitive style that relies on expectations, such that it takes them longer to recognise the extent of discrepancy between expectations and incoming information. Copyright © 2010 John Wiley & Sons, Ltd.

Placebo studies and ritual theory: a comparative analysis of Navajo, acupuncture and biomedical healing

Using a comparative analysis of Navajo healing ceremonials, acupuncture and biomedical treatment, this essay examines placebo studies and ritual theory as mutually interpenetrating disciplines. Healing rituals create a receptive person susceptible to the influences of authoritative culturally sanctioned 'powers'. The healer provides the sufferer with imaginative, emotional, sensory, moral and aesthetic input derived from the palpable symbols and procedures of the ritual process-in the process fusing the sufferer's idiosyncratic narrative unto a universal cultural mythos. Healing rituals involve a drama of evocation, enactment, embodiment and evaluation in a charged atmosphere of hope and uncertainty. Experimental research into placebo effects demonstrates that routine biomedical pharmacological and procedural interventions contain significant ritual dimensions. This research also suggests that ritual healing not only represents changes in affect, self-awareness and self-appraisal of behavioural capacities, but involves modulations of symptoms through neurobiological mechanisms. Recent scientific investigations into placebo acupuncture suggest several ways that observations from ritual studies can be verified experimentally. Placebo effects are often described as 'non-specific'; the analysis presented here suggests that placebo effects are the 'specific' effects of healing rituals.

The relation of emotions to placebo responses

The hypothesis put forth is that expectations of treatment effects reduce negative emotions and thereby reduce symptoms, e.g. pain. Negative emotions increase pain, and it is hypothesized that placebos reduce pain by reducing negative emotions, i.e. feelings of nervousness, fear and anxiety. Placebo analgesia has been shown to be mediated via opioid activity, and relaxation increases opioid activity. The placebo acquires its relaxing effect due to verbal information that pain will be reduced, or due to associations between the placebo and the reduction in pain after effective treatment. Thus, the placebo signals that unpleasantness will be less after administration of the placebo. This involves negative reinforcement which is due to activation of a dopaminergic system that has been found to be activated during placebo analgesia and is involved in positive emotions. The nocebo effect of increased pain is, consistent with this model, because of increased fear and anxiety. The new aspect of the presented model is the hypothesis that expectations reduce negative emotions, and that negative reinforcement that involves the dopaminergic reinforcement system should be a contributor to placebo responses.

The Role of Attributional Bias and Visual Stress on the Improvement of Reading Speed Using Colored Filters

This study tested the predictions derived from two explanatory theoretical models of the effects of colored filters on reading speed: the theory of attributional bias and the theory of visual stress associated with reading. The experimental group consisted of 27 secondary school students (14 boys, 13 girls) diagnosed with the Meares-Irlen syndrome; the control group had 27 students paired in age and sex with the experimental group. The mean age of the sample was 12 years, 10 months ( SD = 8.9 mo.). The effects of colored filters on reading speed and accuracy were tested using a word reading test and a visual stress induction text. The presentation method tapped individuals' visual sensitivity and response criteria. The results support some predictions of the theory of attributional bias, but more research is needed to assess each theory of reading speed.

Role of central neurophysiological systems in placebo analgesia and their relationships with cognitive processes mediating placebo responding

The harnessing of the positive aspects of the placebo effect in clinical practice is a major clinical and ethical challenge, and requires better understanding of placebo mechanisms. In this article, we present an explanatory cognitive model of placebo analgesia, centered on expectation of pain relief, and present direct and indirect evidence for the psychological and physiological drivers and downstream mediators of the effects of expectation on reduction in pain. The endogenous opioid system is involved in expectation-mediated analgesia, but it is not known whether this system is required for the generation or downstream effects of expectation. There is indirect evidence to support the role of other neurotransmitter systems, such as the serotonergic and dopamine systems, and a possible role of the hypothalamic–pituitary–adrenal stress axis. The future challenge is the identification of the causal role of these systems in placebo analgesia, which would provide an empirical basis for exploring new pain therapies.

Placebo effect studies are susceptible to response bias and to other types of biases

OBJECTIVE

Investigations of the effect of placebo are often challenging to conduct and interpret. The history of placebo shows that assessment of its clinical significance has a real potential to be biased. We analyze and discuss typical types of bias in studies on placebo.

STUDY DESIGN AND SETTING

A methodological analysis and discussion.

RESULTS

The inherent nonblinded comparison between placebo and no-treatment is the best research design we have in estimating effects of placebo, both in a clinical and in an experimental setting, but the difference between placebo and no-treatment remains an approximate and fairly crude reflection of the true effect of placebo interventions. A main problem is response bias in trials with outcomes that are based on patients' reports. Other biases involve differential co-intervention and patient dropouts, publication bias, and outcome reporting bias. Furthermore, extrapolation of results to a clinical settings are challenging because of a lack of clear identification of the causal factors in many clinical trials, and the nonclinical setting and short duration of most laboratory experiments.

CONCLUSIONS

Creative experimental efforts are needed to assess rigorously the clinical significance of placebo interventions and investigate the component elements that may contribute to the therapeutic benefit.

Interaction between expectancies and drug effects: an experimental investigation of placebo analgesia with caffeine as an active placebo

RATIONALE

In a randomised placebo-controlled clinical trial it is assumed that psychosocial effects of the treatment, regression to the mean and spontaneous remission are identical in the drug and placebo group. Consequently, any difference between the groups can be ascribed to the pharmacological effects. Previous studies suggest that side effects of drugs can enhance expectancies of treatment effects in the drug group compared to the placebo group, and thereby increase placebo responses in the drug group compared to the placebo group.

OBJECTIVES

The hypothesis that side effects of drugs can enhance expectancies and placebo responses was tested.

METHOD

Painful laser stimuli were delivered to 20 healthy subjects before and after administration of a drink with 0 or 4 mg/kg caffeine. The drink was administered either with information that it contained a painkiller or that it was a placebo. Laser-evoked potentials and reports of pain, expectancy, arousal and stress were measured.

RESULTS

Four milligrammes per kilogramme of caffeine reduced pain. Information that a painkiller was administered increased the analgesic effect of caffeine compared to caffeine administered with no drug information. This effect was mediated by expectancies. Information and expectancies had no effect on pain intensity when 0 mg/kg was administered.

CONCLUSION

The analgesic effect of caffeine was increased by information that a painkiller was administered. This was due to an interaction of the pharmacological action of the drug and expectancies. Hence, psychosocial effects accompanying a treatment can differ when an active drug is administered compared to a placebo.

An exploratory study on the effects of an expectancy manipulation on chemotherapy-related nausea

CONTEXT

Previous research has shown that the effectiveness of acupressure bands in reducing chemotherapy-related nausea is related to patients' expectations of efficacy.

OBJECTIVE

To test whether an informational manipulation designed to increase expectation of efficacy regarding acupressure bands would enhance their effectiveness.

METHODS

We conducted an exploratory, four-arm, randomized clinical trial in breast cancer patients about to begin chemotherapy. All patients received acupressure bands and a relaxation CD. This report focuses on Arm 1(expectancy-neutral informational handout and CD) compared with Arm 4 (expectancy-enhancing handout and CD). Randomization was stratified according to the patient's level of certainty that she would have treatment-induced nausea (two levels: high and low). Experience of nausea and use of antiemetics were assessed with a five-day diary.

RESULTS

Our expectancy-enhancing manipulation resulted in improved control of nausea in the 26 patients with high nausea expectancies but lessened control of nausea in 27 patients having low nausea expectancies. This interaction effect (between expected nausea and intervention effectiveness) approached statistical significance for our analysis of average nausea (P=0.084) and reached statistical significance for our analysis of peak nausea (P=0.030). Patients receiving the expectancy-enhancing manipulation took fewer antiemetic pills outside the clinic (mean(enhanced)=12.6; mean(neutral)=18.5, P=0.003).

CONCLUSION

This exploratory intervention reduced antiemetic use overall and also reduced nausea in patients who had high levels of expected nausea. Interestingly, it increased nausea in patients who had low expectancies for nausea. Confirmatory research is warranted.

Placebo analgesia as a case of a cognitive style driven by prior expectation

Placebo analgesia has been shown to be driven by expectations of treatment effects. We suggest that the expectation of treatment creates uncertainty about the sensory information of pain. We tested the hypothesis that in placebo responders uncertainty generated by expectations generalizes to other cognitive processes by recruiting participants for a placebo study who had previously taken part in a visual cue-picture decision making perceptual task. The task investigated how participants utilised prior cues against discrepant and uncertain sensory information. Participants were selected based on their degree of acquiescence in the cue-picture task. The placebo experiment was split into three blocks of pre-treatment, treatment and post-treatment. Participants were told that they may or may not receive an anaesthetic cream on one arm. However, all participants received inactive cream paired with non-painful stimuli during the treatment block. Electroencephalography (EEG) was used to measure pain evoked potentials to laser heat to determine if the behavioural misperception of pain translated into a physiological response. Regression models showed that both behavioural and physiological placebo responses could be predicted by participants' scores of acquiescence in the cue-picture decision making task. Placebo analgesia seems to be influenced by a cognitive style that assimilates responses to expectations increasing the chances of error when detecting discrepant sensory information.

Comparison of two types of epidemiological surveys aimed at collecting daily clinical symptoms in community-based longitudinal studies

BACKGROUND

Investigators use prospective community-based studies to collect longitudinal information on childhood diarrhea. The interval in which data are collected may affect the accuracy and interpretation of results. Our objective was to compare data of reported daily clinical symptoms from surveys conducted daily versus twice-weekly surveys.

METHODS

We conducted our study in Lima, Peru, between October and December 2007. We asked 134 mothers to report daily symptoms by using a twice-weekly survey. We conducted daily surveys for the same data on 25% of participants randomly selected each day. We analyzed intersurvey variability by using Cohen's kappa and Signal Detection Theory (SDT).

RESULTS

We collected 6157 and 1181 child-days of data through the twice-weekly and daily surveys, respectively. The prevalence of diarrhea, fever, vomiting, and cough were 6.4%, 1.6%, 2.1%, and 22.7% from the twice-weekly survey and, 6.4%, 2.0%, 2.4%, and 26% from the daily survey, respectively. Despite similar prevalence, 20% of days with reported diarrhea were discrepant between the two surveys, and agreement in the report of diarrhea decreased as time between the interviews increased (p = .03).

CONCLUSIONS

Although twice-weekly surveys provide an adequate estimate of diarrheal prevalence compared with daily surveys, the prevalence of other symptoms based on dichotomous questions was lower under the former. Additionally, the agreement between the two surveys in the report of diarrhea decreased as the recall period increased, suggesting that data from daily interviews were of greater quality. Our analysis is a novel application of SDT to measure respondent certainty and bias, from which better inference about the quality of collected data may be drawn.

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.

"Maybe I made up the whole thing": placebos and patients' experiences in a randomized controlled trial

Patients in the placebo arms of randomized controlled trials (RCT) often experience positive changes from baseline. While multiple theories concerning such "placebo effects" exist, peculiarly, none has been informed by actual interviews of patients undergoing placebo treatment. Here, we report on a qualitative study (n = 27) embedded within a RCT (n = 262) in patients with irritable bowel syndrome. Besides identical placebo acupuncture treatment in the RCT, the qualitative study patients also received an additional set of interviews at the beginning, midpoint, and end of the trial. Interviews of the 12 qualitative subjects who underwent and completed placebo treatment were transcribed. We found that patients (1) were persistently concerned with whether they were receiving placebo or genuine treatment; (2) almost never endorsed "expectation" of improvement but spoke of "hope" instead and frequently reported despair; (3) almost all reported improvement ranging from dramatic psychosocial changes to unambiguous, progressive symptom improvement to tentative impressions of benefit; and (4) often worried whether their improvement was due to normal fluctuations or placebo effects. The placebo treatment was a problematic perturbation that provided an opportunity to reconstruct the experiences of the fluctuations of their illness and how it disrupted their everyday life. Immersion in this RCT was a co-mingling of enactment, embodiment and interpretation involving ritual performance and evocative symbols, shifts in bodily sensations, symptoms, mood, daily life behaviors, and social interactions, all accompanied by self-scrutiny and re-appraisal. The placebo effect involved a spectrum of factors and any single theory of placebo--e.g. expectancy, hope, conditioning, anxiety reduction, report bias, symbolic work, narrative and embodiment--provides an inadequate model to explain its salubrious benefits.

Effects of placebo interventions on gastric motility and general autonomic activity

OBJECTIVE

The study aimed to investigate placebo effects on gastric motility and to examine possible autonomic mediating mechanisms.

METHODS

Eighteen healthy volunteers received a placebo pill on three occasions together with the verbal suggestion that it would stimulate, relax, or not affect gastric activity. Electrogastrogram, electrocardiogram, and electrodermal activity recordings were conducted for 30 min prior to and following intervention.

RESULTS

Dominant frequency of the gastric slow wave decreased in the stimulant condition, and increased in the relaxant condition, the difference among conditions being significant. No differential effects of the interventions on cardiac interbeat intervals, heart rate variability, and skin conductance levels were observed.

CONCLUSION

Stomach relaxant and stimulant placebo interventions modulated gastric motility independently from changes in general autonomic activity.

Gender and the nocebo response following conditioning and expectancy

OBJECTIVE

To investigate the role of Pavlovian conditioning and expectancy and of gender on the nocebo effects.

METHODS

Conditioning experiment: Forty-eight healthy male and female volunteers were investigated for 3 days using a standard rotation procedure. Subjects in the experimental group received a salient oral stimulus prior to rotation; subjects in the control group received the stimulus 12 h after rotations on Days 1 and 2; on Day 3, all subjects received the stimulus prior to rotation. Expectancy experiment: Another 48 healthy subjects were rotated 5 x 1 min once only. All subjects received the same oral stimulus immediately prior to rotation; subjects in the experimental group were told that the symptoms might worsen with the stimulus; controls did not receive additional information. In both experiments, symptom rating (SR) and rotation tolerance (RT) were determined.

RESULTS

Conditioning significantly reduced RT (P=.015) and increased SR (P=.024). For both RT and SR, a significant "day x group x gender" effect was found (P=.044; SR: P=.011) indicating that conditioning was more effective in women. Expectancies lowered RT (P=.085) without affecting SR. There was a significant "rotation x gender" interaction on RT (P=.005) indicating that the expectancy was more effective in men.

CONCLUSION

Women responded stronger to conditioning while men responded to expectancies, but to a lesser degree. It needs to be determined whether this is restricted to nausea-specific conditions or can be generalized across clinical and experimental conditions.

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.

[Clinical significance of the placebo effect]

Placebo controlled studies examining clinical problems, e.g. in pain therapy, are considered the "gold standard" for evidence-based medicine. In these studies the placebo effect itself is not the main focus of interest, but serves more as a control for the specificity of the effect of a certain treatment. What physicians in this context often do not realize is that the placebo effect itself represents a true measurable correlate of an organism's psycho-neurobiological response and, thereby, influences the healing process, e.g. the pain relief. Placebo is, therefore, not equivalent to "no treatment". The number of placebo responders, the degree and the duration of the placebo effect is not fixed, but are subject to a much greater variability then hitherto believed. The myth that placebo responders have a certain personality has not been proven correct; instead, the relationships between physicians and patients as well as sociocultural factors have a considerable impact on the placebo effect. Psychological theories explain that classical conditioning, enhanced expectation and motivation of the patient determine the degree of the placebo effect. These directly influence neurobiological systems such as the endogenous opioids which according to modern brain imaging are predominantly activated in pain-relevant areas and contribute to the effect of placebo analgesia. Placebo effects that should be deliberately excluded in controlled clinical trials, can be desirable in clinical practice to optimize the total therapeutic effect. This should mean that the context effect of each therapeutic intervention is maximized towards an improved therapeutic effect, as outlined in the recent AWMF guidelines for postoperative pain therapy, but should not include the administration of an inert substance. The latter is controlled by rigorous ethical guidelines and is only permitted in the context of ethically approved controlled clinical trials. A possible alternative is suggested by Benedetti et al. in which the hidden administration of an active substance identifies the specific response in contrast to the open application of the same substance characterizing the specific plus the placebo effect, after which the pure placebo effect can be determined.

Components of placebo effect: randomised controlled trial in patients with irritable bowel syndrome

OBJECTIVE

To investigate whether placebo effects can experimentally be separated into the response to three components-assessment and observation, a therapeutic ritual (placebo treatment), and a supportive patient-practitioner relationship-and then progressively combined to produce incremental clinical improvement in patients with irritable bowel syndrome. To assess the relative magnitude of these components.

DESIGN

A six week single blind three arm randomised controlled trial.

SETTING

Academic medical centre.

PARTICIPANTS

262 adults (76% women), mean (SD) age 39 (14), diagnosed by Rome II criteria for and with a score of > or =150 on the symptom severity scale.

INTERVENTIONS

For three weeks either waiting list (observation), placebo acupuncture alone ("limited"), or placebo acupuncture with a patient-practitioner relationship augmented by warmth, attention, and confidence ("augmented"). At three weeks, half of the patients were randomly assigned to continue in their originally assigned group for an additional three weeks.

MAIN OUTCOME MEASURES

Global improvement scale (range 1-7), adequate relief of symptoms, symptom severity score, and quality of life.

RESULTS

At three weeks, scores on the global improvement scale were 3.8 (SD 1.0) v 4.3 (SD 1.4) v 5.0 (SD 1.3) for waiting list versus "limited" versus "augmented," respectively (P<0.001 for trend). The proportion of patients reporting adequate relief showed a similar pattern: 28% on waiting list, 44% in limited group, and 62% in augmented group (P<0.001 for trend). The same trend in response existed in symptom severity score (30 (63) v 42 (67) v 82 (89), P<0.001) and quality of life (3.6 (8.1) v 4.1 (9.4) v 9.3 (14.0), P<0.001). All pairwise comparisons between augmented and limited patient-practitioner relationship were significant: global improvement scale (P<0.001), adequate relief of symptoms (P<0.001), symptom severity score (P=0.007), quality of life (P=0.01). Results were similar at six week follow-up.

CONCLUSION

Factors contributing to the placebo effect can be progressively combined in a manner resembling a graded dose escalation of component parts. Non-specific effects can produce statistically and clinically significant outcomes and the patient-practitioner relationship is the most robust component.

TRIAL REGISTRATION

Clinical Trials NCT00065403.

Experimental designs and brain mapping approaches for studying the placebo analgesic effect

The placebo effect has intrigued scientists since it was proposed. The debate has now centered on how it works. Significant progress has been made and most of our knowledge about the neurobiological mechanisms comes from the field of pain and analgesia. The appropriateness of the experimental/clinical paradigms is crucial when we want to investigate the mechanisms of the placebo phenomenon. Recently, functional imaging techniques, such as positron emission tomography, magnetic resonance imaging, and electro/magnetoencephalography have also given the opportunity to define the neuroanatomical bases of placebo analgesia. This work systematically reviews the literature that deals with placebo analgesia, emphasizing both the methodological aspects and the neurobiological advances. The understanding of placebo mechanisms is fundamental and necessary to identify ways of accessing and harnessing these mechanisms in clinical practice to the patient's benefit.

New insights into placebo analgesia

PURPOSE OF REVIEW

The placebo effect is a widespread phenomenon in medicine, both in clinical trials and in routine medical practice. Most of our knowledge about the underlying psychological and physiological mechanisms comes from the study of placebo analgesia.

RECENT FINDINGS

When the correct methodological approach is used, striking placebo effects can be detected and these can be mediated by conscious anticipatory processes or unconscious conditioning mechanisms. However, it should be stressed that many improvements observed after the administration of a placebo are not real placebo effects, but different phenomena such as spontaneous remission, regression to the mean and symptom detection ambiguity. Both neuropharmacological studies and brain imaging investigations show that placebo analgesia is mediated by endogenous opioids. Moreover, we also know that during placebo analgesia other systems change their functions, like the respiratory centres and the cardiovascular system. The placebo effect has also been approached from a different perspective by administering analgesics covertly. The results show that hidden medical treatments are less effective than open ones.

SUMMARY

The understanding of the placebo effect may lead to better design of clinical trials and better medical practice. For example, it can be used in therapeutic protocols aimed at reducing drug intake.

Evidence for placebo effects on physical but not on biochemical outcome parameters: a review of clinical trials

BACKGROUND

Recent reviews on placebo effects in clinical trials suggest that objective changes following placebo treatments may not exist or, at least, have been considerably overestimated. However, the possibility that yet unidentified subsets of parameters are responsive to placebo treatments has not been taken into account. Therefore, the aim of the present study is to examine the effects of placebo treatments on objectively measured outcome parameters by specifically focusing on peripheral disease processes.

METHODS

An initial dataset was collected from a MEDLINE search for placebo-controlled, randomized clinical trials. Trials with stable disease conditions were identified, and the effects of placebo treatments on peripheral outcome parameters were estimated by the changes from baseline in the placebo groups. An explorative data analysis was conducted in order to identify parameter classes with differential responsiveness to placebo treatments. A subgroup meta-analysis of a second dataset was performed to test whether the preliminary classification would also apply to placebo effects derived from the comparison of placebo groups with untreated control groups.

RESULTS

The explorative analysis of outcome parameters and strength of placebo effects yielded a classification into responsive "physical" versus non-responsive "biochemical" parameters. In total, 50% of trials measuring physical parameters showed significant placebo effects, compared with 6% of trials measuring biochemical parameters. A subgroup meta-analysis substantiated the differential response (physical parameters: n = 14, Hedges' pooled effect size g = 0.34, 95% CI 0.22 to 0.46; biochemical parameters: n = 15, g = 0.03, 95% CI -0.04 to 0.10). The subanalysis of the second dataset supported the classification and revealed a significant improvement for physical parameters (n = 20, g = 0.22, 95% CI 0.07 to 0.36) and a deterioration for biochemical parameters (n = 6, g = -0.17, 95% CI -0.31 to -0.02).

CONCLUSION

The results suggest that placebo interventions can improve physical disease processes of peripheral organs more easily and effectively than biochemical processes. This differential response offers a good starting point for theoretical considerations on possible mediating mechanisms, and for future investigations in this field.

Placebo and endogenous mechanisms of analgesia

The discovery of the endogenous systems of analgesia has produced a large amount of research aimed at investigating their biochemical and neurophysiological mechanisms and their neuroanatomical localization. Nevertheless, the neurobiological acquisitions on these mechanisms have not been paralleled by behavioural correlates in humans--in other words, by the understanding of when and how these endogenous mechanisms of analgesia are activated. Until recent times one of the most studied behavioural correlates of endogenous analgesia was stress-induced analgesia, in which the activation of endogenous opioid systems is known to be involved. By contrast, today the placebo analgesic effect represents one of the best-described situations in which this endogenous opioid network is naturally activated in humans. Therefore, not only is placebo research helpful towards improving clinical trial design and medical practice, but it also provides us with a better understanding of the endogenous mechanisms of analgesia.