The placebo effect: From concepts to genes

Will human-like machines make human-like mistakes?

Although we agree with Lake et al.'s central argument, there are numerous flaws in the way people use causal models. Our models are often incorrect, resistant to correction, and applied inappropriately to new situations. These deficiencies are pervasive and have real-world consequences. Developers of machines with similar capacities should proceed with caution.

The Placebo Phenomenon: A Narrow Focus on Psychological Models

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

Network analysis of the genomic basis of the placebo effect

The placebo effect is a phenomenon in which patients who are given an inactive treatment (e.g., inert pill) show a perceived or actual improvement in a medical condition. Placebo effects in clinical trials have been investigated for many years especially because placebo treatments often serve as the control arm of randomized clinical trial designs. Recent observations suggest that placebo effects may be modified by genetics. This observation has given rise to the term "placebome," which refers to a group of genome-related mediators that affect an individual's response to placebo treatments. In this study, we conduct a network analysis of the placebome and identify a placebome module in the comprehensive human interactome using a seed-connector algorithm. The placebome module is significantly enriched with neurotransmitter signaling pathways and brain-specific proteins. We validate the placebome module using a large cohort of the Women's Genome Health Study (WGHS) trial and demonstrate that the placebome module is significantly enriched with genes whose SNPs modify the outcome in the placebo arm of the trial. To gain insights into placebo effects in different diseases and drug treatments, we use a network proximity measure to examine the closeness of the placebome module to different disease modules and drug target modules. The results demonstrate that the network proximity of the placebome module to disease modules in the interactome significantly correlates with the strength of the placebo effect in the corresponding diseases. The proximity of the placebome module to molecular pathways affected by certain drug classes indicates the existence of placebo-drug interactions. This study is helpful for understanding the molecular mechanisms mediating the placebo response, and sets the stage for minimizing its effects in clinical trials and for developing therapeutic strategies that intentionally engage it.

Placebo and Nocebo Effects: The Advantage of Measuring Expectations and Psychological Factors

Several studies have explored the predictability of placebo and nocebo individual responses by investigating personality factors and expectations of pain decreases and increases. Psychological factors such as optimism, suggestibility, empathy and neuroticism have been linked to placebo effects, while pessimism, anxiety and catastrophizing have been associated to nocebo effects. We aimed to investigate the interplay between psychological factors, expectations of low and high pain and placebo hypoalgesia and nocebo hyperalgesia. We studied 46 healthy participants using a well-validated conditioning paradigm with contact heat thermal stimulations. Visual cues were presented to alert participants about the level of intensity of an upcoming thermal pain. We delivered high, medium and low levels of pain associated with red, yellow and green cues, respectively, during the conditioning phase. During the testing phase, the level of painful stimulations was surreptitiously set at the medium control level with all the three cues to measure placebo and nocebo effects. We found both robust placebo hypolagesic and nocebo hyperalgesic responses that were highly correlated with expectancy of low and high pain. Simple linear regression analyses showed that placebo responses were negatively correlated with anxiety severity and different aspects of fear of pain (e.g., medical pain, severe pain). Nocebo responses were positively correlated with anxiety sensitivity and physiological suggestibility with a trend toward catastrophizing. Step-wise regression analyses indicated that an aggregate score of motivation (value/utility and pressure/tense subscales) and suggestibility (physiological reactivity and persuadability subscales), accounted for the 51% of the variance in the placebo responsiveness. When considered together, anxiety severity, NEO openness-extraversion and depression accounted for the 49.1% of the variance of the nocebo responses. Psychological factors per se did not influence expectations. In fact, mediation analyses including expectations, personality factors and placebo and nocebo responses, revealed that expectations were not influenced by personality factors. These findings highlight the potential advantage of considering batteries of personality factors and measurements of expectation in predicting placebo and nocebo effects related to experimental acute pain.

Nocebo and pain: An overview of the psychoneurobiological mechanisms

INTRODUCTION

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

PURPOSE

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

METHOD

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

FINDINGS

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

IMPLICATIONS

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

Placebo Intervention Enhances Reward Learning in Healthy Individuals

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

Randomised placebo-controlled trials of surgery: ethical analysis and guidelines

Use of a placebo control in surgical trials is a divisive issue. We argue that, in principle, placebo controls for surgery are necessary in the same way as for medicine. However, there are important differences between these types of trial, which both increase justification and limit application of surgical studies. We propose that surgical randomised placebo-controlled trials are ethical if certain conditions are fulfilled: (1) the presence of equipoise, defined as a lack of unbiased evidence for efficacy of an intervention; (2) clinically important research question; (3) the risk to patients is minimised and reasonable; (4) there is uncertainty about treatment allocation rather than deception; (5) there is preliminary evidence for efficacy, which justifies a placebo-controlled design; and (6) ideally, the placebo procedure should have some direct benefit to the patient, for example, as a diagnostic tool. Placebo-controlled trials in surgery will most often be justified when surgery is performed to improve function or relieve symptoms and when objective outcomes are not available, while the risk of mortality or significant morbidity is low. In line with medical placebo-controlled trials, the surgical trial (1) should be sufficiently powered and (2) standardised so that its results are valid, (3) consent should be valid, (4) the standard treatment or rescue medication should be provided if possible, and (5) after the trial, the patients should be told which treatment they received and there should be provision for post-trial care if the study may result in long-term negative effects. We comment and contrast our guidelines with those of the American Medical Association.

How to prove that your therapy is effective, even when it is not: a guideline

AIMS

Suppose you are the developer of a new therapy for a mental health problem or you have several years of experience working with such a therapy, and you would like to prove that it is effective. Randomised trials have become the gold standard to prove that interventions are effective, and they are used by treatment guidelines and policy makers to decide whether or not to adopt, implement or fund a therapy.

METHODS

You would want to do such a randomised trial to get your therapy disseminated, but in reality your clinical experience already showed you that the therapy works. How could you do a trial in order to optimise the chance of finding a positive effect?

RESULTS

Methods that can help include a strong allegiance towards the therapy, anything that increases expectations and hope in participants, making use of the weak spots of randomised trials (risk of bias), small sample sizes and waiting list control groups (but not comparisons with existing interventions). And if all that fails one can always not publish the outcomes and wait for positive trials.

CONCLUSIONS

Several methods are available to help you show that your therapy is effective, even when it is not.

Relieving pain using dose-extending placebos: a scoping review

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

Effect of acupuncture and instruction on physiological recovery from maximal exercise: a balanced-placebo controlled trial

Background

This study aimed to investigate the effect of acupuncture administered immediately following a graded exercise test (GXT) on physiological measures of recovery and determine if instruction (expectancy) affected the responses.

Methods

A balanced-placebo 2 × 2 factorial design was used with treatment (real vs placebo acupuncture) and instruction (told real vs told placebo acupuncture) as factors; a no-treatment control group was also included to compare the treatment responses to no treatment. Recreationally active, acupuncture naïve young adults (n = 60) performed a GXT to exhaustion on a cycle ergometer (15 W/min). Heart rate, blood pressure, oxygen consumption, respiratory rate and blood lactate were collected during the test and during 60 min of supine recovery on a plinth. An experienced acupuncturist delivered real or placebo acupuncture within 6 min of completing the GXT (total treatment time = 20 min). Real acupuncture points included Neiguan (PC6), Zusanli (ST36), Lieque (LU7), and Tanzhang (REN17), while placebo acupuncture was delivered using the Park sham needle placed 1–2 cm away from each real acupuncture point. The control group received no intervention.

Results

Linear and quadratic trend analyses over time indicated no significant differences between groups on any dependent variable. However, analysis of specific timepoints (every 10 min of the 60 min recovery) revealed that participants who received some form of treatment had a lower heart rate than participants in the no treatment control group (p = 0.042) at 20 min post-exercise. Further, a significant treatment by instruction interaction effect for heart rate was also found at 50 min (p = 0.042) and 60 min (p = 0.013) post-exercise, indicating that the differences between real and placebo acupuncture were affected by expectancy manipulation. No other significant effects were noted. However, it was interesting to note that participants who believed they were given real acupuncture reported quicker perceived recovery independent of actual treatment (p = 0.006) suggesting that instruction about treatment influenced perceived recovery.

Conclusion

In summary, due to limited evidence, the current study does not support the acute use of acupuncture for exercise recovery. However, importantly, the current study demonstrates that a balanced-placebo design is viable for testing acupuncture and expectancy effects, and this methodology could therefore be implemented in future studies.

Trial registration

ACTRN12612001015831 (Date registered: 20/09/2012).

Rethinking Explicit Expectations: Connecting Placebos, Social Cognition, and Contextual Perception

Expectancy effects are a widespread phenomenon, and they come with a lasting influence on cognitive operations, from basic stimulus processing to higher cognitive functions. Their impact is often profound and behaviorally significant, as evidenced by an enormous body of literature investigating the characteristics and possible processes underlying expectancy effects. The literature on this topic spans diverse fields, from clinical psychology to cognitive neuroscience, and from social psychology to behavioral biology. We present an emerging perspective on these diverse phenomena and show how this perspective stimulates new toeholds for investigation, provides insight in underlying mechanisms, improves awareness of methodological confounds, and can lead to a deeper understanding of the effects of expectations on a broad spectrum of cognitive processes.

Enhance placebo, avoid nocebo: How contextual factors affect physiotherapy outcomes

INTRODUCTION

Placebo and nocebo represent complex and distinct psychoneurobiological phenomena in which behavioural and neurophysiological modifications occur together with the application of a treatment. Despite a better understanding of this topic in the medical field, little is known about their role in physiotherapy.

PURPOSE

The aim of this review is: a) to elucidate the neurobiology behind placebo and nocebo effects, b) to describe the role of the contextual factors as modulators of the clinical outcomes in rehabilitation and c) to provide clinical and research guidelines on their uses.

IMPLICATIONS

The physiotherapist's features, the patient's features, the patient-physiotherapist relationship, the characteristics of the treatment and the overall healthcare setting are all contextual factors influencing clinical outcomes. Since every physiotherapy treatment determines a specific and a contextual effect, physiotherapists should manage the contextual factors as a boosting element of any manual therapy to improve placebo effects and avoid detrimental nocebo effects.

Influence of different positioning of a local pain catheter on postoperative pain after paramedian laparotomy-a blinded, randomized trial

BACKGROUND

Continuous application of local anaesthetics reduces postoperative pain after different approaches for laparotomy. In this randomized, blinded trial, we investigated the effect of continuous application of local anaesthetics after paramedian laparotomy either with subfascial or subcutaneous catheter in addition to a standardized systemic analgesia.

MATERIALS AND METHODS

Patients with stage III/IV melanoma and indication for radical iliac lymph node dissection (RILND) were randomized to a continuous application of a local anaesthetic through either a subfascial or subcutaneous catheter. Participants and those assessing the outcomes were blinded. The main outcome criterion was the pain level on the first postoperative morning while exercising measured with a visual analogue scale. Minor criteria were the pain measured by the area-under-curve until the third postoperative day, the patient's satisfaction with analgesic treatment, the analgesic requirement, the overall complications and the day of discharge.

RESULTS

Fifty-two patients were evaluated. Pain therapy was sufficient in both groups during the postoperative course while resting and during mobilization. There were no significant differences regarding the main and minor outcome criteria. Doses of additional analgesics did not differ between groups. No adverse events or side effects were observed.

CONCLUSION

For patients who undergo paramedian laparotomy, none of the investigated techniques is superior to the other at a median pain level under visual analogue scale (VAS) 30 mm on the first postoperative morning.

TRIAL REGISTRATION NUMBER

DRKS00003632 (German Register of Clinical Trials).

Patient attitudes about the clinical use of placebo: qualitative perspectives from a telephone survey

OBJECTIVES

To examine qualitative responses regarding the use of placebo treatments in medical care in a sample of US patients.Survey studies suggest a deliberate clinical use of placebos by physicians, and prior research has found that although most US patients find placebo use acceptable, the rationale for these beliefs is largely unknown.

SETTING

Members of the Outpatient Clinic at the Kaiser Permanente Northern California interviewed research participants who had been seen for a chronic health problem at least once in the prior 6 months.

PARTICIPANTS

853 women (61%) and men, white (58%) and non-white participants aged 18-75 years.

PRIMARY AND SECONDARY OUTCOMES

Qualitative responses on perceptions of placebo use from one-time telephone surveys were analysed for common themes and associations with demographic variables.

RESULTS

Prior results indicated that a majority of respondents felt it acceptable for doctors to recommend placebo treatments. Our study found that a lack of harm (n=291, 46.1%) and potential benefit (n=250, 39.6%) were the most common themes to justify acceptability of placebo use. Responses citing potential benefit were associated with higher education (r=0.787; p<0.024). Of the minority of respondents who judged it never acceptable for doctors to recommend placebo treatments, the most often referenced rationale was obligation of the doctor to do more (n=102, 48.3%). Additional themes emerged around the issue of whether a doctor was transparent about placebo use, including honesty, patient's right to know and power of the mind. Older age was associated with likelihood to cite overall physician, as opposed to treatment, related themes (r=0.753; p<0.002).

CONCLUSIONS

Participants seem to appreciate and understand the lack of harm and potential benefit associated with placebo treatments, while valuing the role of the physician and the patient in its implementation.

Sources of Placebo-Induced Relief From Nausea: The Role of Instruction and Conditioning

OBJECTIVES

It is well documented that expectancies alter the nauseous response. However, the lack of integration in research examining sources of expectancy has limited our understanding of how expectancies are formed and, consequently, our ability to intervene. The present study explored the role of both instructions and conditioning in placebo-induced relief from nausea.

METHODS

The study used a 2 × 2 between-subjects design with instruction and conditioning as factors with 56 healthy volunteers. The instruction manipulation involved randomizing participants to receive information that a sham treatment (a peppermint essence vapor) would reduce nausea or no such instructions. The conditioning manipulation involved further randomizing participants to have the first administration of this sham treatment paired with a surreptitious reduction in galvanic vestibular stimulation (GVS) intensity or no prior pairing. Nausea was induced through GVS. On test, all groups received the same level of GVS with the sham treatment present.

RESULTS

On test, participants who received instruction had significantly lower nauseous response scores than those who did not (F(1,46) = 6.71, p = .013), and those who received conditioning also reported less nausea than those who did not (F(1,46) = 5.20, p = .027), with the interaction between the two not reaching statistical significance (F(1,46) = 2.33, p = .13).

CONCLUSIONS

These findings indicate that placebo responding in nausea can be induced both through positive instructions and as little as one pairing of a treatment with a reduction in nausea, as well as their combination. This suggests that using placebo effects to complement antiemetic therapy may offer an important method of further reducing nausea in the clinic.

Power calculations and placebo effect for future clinical trials in progressive supranuclear palsy

BACKGROUND

Two recent randomized, placebo-controlled trials of putative disease-modifying agents (davunetide, tideglusib) in progressive supranuclear palsy (PSP) failed to show efficacy, but generated data relevant for future trials.

METHODS

We provide sample size calculations based on data collected in 187 PSP patients assigned to placebo in these trials. A placebo effect was calculated.

RESULTS

The total PSP-Rating Scale required the least number of patients per group (N = 51) to detect a 50% change in the 1-year progression and 39 when including patients with ≤ 5 years disease duration. The Schwab and England Activities of Daily Living required 70 patients per group and was highly correlated with the PSP-Rating Scale. A placebo effect was not detected in these scales.

CONCLUSIONS

We propose the 1-year PSP-Rating Scale score change as the single primary readout in clinical neuroprotective or disease-modifying trials. The Schwab and England Activities of Daily Living could be used as a secondary outcome. © 2016 International Parkinson and Movement Disorder Society.

A Review of 21st Century Utility of a Biopsychosocial Model in United States Medical School Education

BACKGROUND

Current medical practice is grounded in a biomedical model that fails to effectively address multifaceted lifestyle and morbidogenic environmental components that are the root causes of contemporary chronic diseases. Utilizing the biopsychosocial (BPS) model in medical school training may produce competent healthcare providers to meet the challenge of rising chronic illnesses that are a result of these factors. This study explored the current trend of research on the utility of the BPS model in medical education and examined medical school curricula that have explicitly adopted the BPS model.

METHODS

A systematic review of peer-reviewed literature was conducted on the BPS model and medical education since the 1970s using multiple databases. Descriptive analysis was used to illustrate findings regarding the trends of the BPS model in medical education and its utility in specific medical schools in the United States.

RESULTS

Major findings illustrated a growing trend in research on the BPS model in medical education since the 1970s with literature in this area most visible since 2000. The same trend was established for the incorporation of psychosocial or behavioral and social science components in medical education. From our peer-reviewed literature search, only 5 medical schools featured utility of the BPS model in their curricula utilizing variable educational processes.

CONCLUSION

Although literature regarding the BPS model in medical education is growing, the explicit utility of the BPS model in medical school is limited. Our findings can stimulate educational processes and research endeavors to advance medical education and medical practice to ensure that future doctors can meet the challenge of rising lifestyle and environmental associated illnesses.