Effects of subtle cognitive manipulations on placebo analgesia - An implicit priming study

Background

Expectancy is widely accepted as a key contributor to placebo effects. However, it is not known whether non‐conscious expectancies achieved through semantic priming may contribute to placebo analgesia. In this study, we investigated if an implicit priming procedure, where participants were unaware of the intended priming influence, affected placebo analgesia.

Methods

In a double‐blind experiment, healthy participants (n = 36) were randomized to different implicit priming types; one aimed at increasing positive expectations and one neutral control condition. First, pain calibration (thermal) and a credibility demonstration of the placebo analgesic device were performed. In a second step, an independent experimenter administered the priming task; Scrambled Sentence Test. Then, pain sensitivity was assessed while telling participants that the analgesic device was either turned on (placebo) or turned off (baseline). Pain responses were recorded on a 0–100 Numeric Response Scale.

Results

Overall, there was a significant placebo effect (p < 0.001), however, the priming conditions (positive/neutral) did not lead to differences in placebo outcome. Prior experience of pain relief (during initial pain testing) correlated significantly with placebo analgesia (p < 0.001) and explained 34% of placebo variance. Trait neuroticism correlated positively with placebo analgesia (p < 0.05) and explained 21% of placebo variance.

Conclusions

Priming is one of many ways to influence behaviour, and non‐conscious activation of positive expectations could theoretically affect placebo analgesia. Yet, we found no SST priming effect on placebo analgesia. Instead, our data point to the significance of prior experience of pain relief, trait neuroticism and social interaction with the treating clinician.

Significance

Our findings challenge the role of semantic priming as a behavioural modifier that may shape expectations of pain relief, and affect placebo analgesia.

Visual Imagery, Various Muscle States and Desensitization Procedures

30 Ss were asked to imagine 8 different scenes in each of three conditions: muscle relaxation, muscle tension, and usual muscle state. Degree of muscle tension significantly affected the quality of the imagery. Tension resulted in images which were described as more active, more frightening, more out of proportion, less friendly, less attractive, and as containing louder sounds and poorer solutions. Ss also reported feeling more a part of the scene and less safe in the tension condition. No significant differences were found in the vividness or clarity of imagery among three conditions. Implications for desensitization and related therapies are discussed.

Imaginative Suggestibility and Hypnotizability

More than a half-century of research aimed at identifying the predictors of hypnotic responding has been described as investigations of “hypnotizability.” Most of that research, however, has disregarded the well-established findings that (a) people respond to suggestion without being hypnotized almost as much as they do following a hypnotic induction, and (b) nonhypnotic and hypnotic suggestibility are highly correlated. More recent studies have provided the first empirical data on predictors of individual differences in response to the induction of hypnosis. These studies indicate that individual differences in hypnotic suggestibility can be accounted for completely by nonhypnotic suggestibility, expectancy, motivation, and reaction time. Because the amount of variance accounted for is as great as the reliability of the hypnotic-suggestibility scale, and because nonhypnotic suggestibility has been controlled, no additional variables are necessary to account for hypnotic suggestibility.

Facilitated Communication as an Ideomotor Response

Forty college students were taught facilitated communication via a commercially available training videotape. They were then asked to facilitate the communication of a confederate, who was described as developmentally disabled and unable to speak. All 40 participants produced responses that they attributed at least partially to the confederate, and most attributed all of the communication entirely to her. Eighty-nine percent produced responses corresponding to information they had received, most of which was unknown to the confederate. Responding was significantly correlated with simple ideomotor responses with a pendulum and was not affected by information about the controversy surrounding facilitated communication. These data support the hypothesis that facilitated communication is an instance of automatic writing, akin to that observed in hypnosis and with Ouija boards, and that the ability to produce automatic writing is more common than previously thought.

Mechanisms of Placebo Pain Reduction: An Empirical Investigation

Identical experimental pain stimuli were applied to the right and left index fingers of 56 university students, following the application of a placebo in the guise of a topical anesthetic to one of the fingers The pain stimuli were administered simultaneously to treated and untreated fingers for half of the subjects and sequentially for the others Significant and equivalent reductions in pain were reported in both conditions as a function of placebo administration These data indicate that reductions of experimental pain produced by placebos presented in the guise of local anesthetics are not mediated by such global mechanisms as anxiety reduction or the release of endogenous opioids

Not seeing or feeling is still believing: conscious and non-conscious pain modulation after direct and observational learning

Our experience with the world is shaped not only directly through personal exposure but also indirectly through observing others and learning from their experiences. Using a conditioning paradigm, we investigated how directly and observationally learned information can affect pain perception, both consciously and non-consciously. Differences between direct and observed cues were manifest in higher pain ratings and larger skin conductance responses to directly experienced cues. However, the pain modulation effects produced by conditioning were of comparable magnitude for direct and observational learning. These results suggest that social observation can induce positive and negative pain modulation. Importantly, the fact that cues learned by observation and activated non-consciously still produced a robust conditioning effect that withstood extinction highlights the role of indirect exposure in placebo and nocebo effects.

Moderation of antidepressant and placebo outcomes by baseline severity in late-life depression: A systematic review and meta-analysis

BACKGROUND

Baseline severity is a crucial moderator of trial outcomes in adult depression, with the advantage of antidepressants over placebo increasing as severity increases. However, this relationship has not been examined in late-life depression.

METHODS

PubMed, Embase, Web of Science, PsycINFO, and Cochrane were searched for studies published through September 2014. Randomized, acute phase, and double-blind studies comparing an antidepressant group with a placebo group in depressed elderly patients were included.

RESULTS

Nineteen studies met all inclusion criteria. Within-group effect sizes revealed significant improvement in antidepressant groups (g=1.35, p<.000), as well as in placebo groups (g=.96, p<.000). Change in depressive symptoms assessed by Hamilton Depression Rating Scale (HDRS) was moderated by baseline severity in antidepressant groups (Z=2.67, p=.008) and placebo groups (Z=4.46, p<.000). However, this would be expected as a result of regression toward the mean, and mean differences between groups did not increase (r=.19, p=.469) as a function of baseline severity.

LIMITATIONS

Limited to published data and information was only analyzed at the level of treatment groups.

CONCLUSION

Baseline severity was not associated with an antidepressant-placebo difference and placebo responses are large in the treatment of depressed elderly people. We propose a stepwise approach, i.e., to initially offer elderly depressed patients psychosocial interventions and only consider antidepressants if patients do not respond.

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.

Empirically derived criteria cast doubt on the clinical significance of antidepressant-placebo differences

Meta-analyses indicate that antidepressants are superior to placebos in statistical terms, but the clinical relevance of the differences has not been established. Previous suggestions of clinically relevant effect sizes have not been supported by empirical evidence. In the current paper we apply an empirical method that consists of comparing scores obtained on the Hamilton rating scale for depression (HAM-D) and scores from the Clinical Global Impressions-Improvement (CGI-I) scale. This method reveals that a HAM-D difference of 3 points is undetectable by clinicians using the CGI-I scale. A difference of 7 points on the HAM-D, or an effect size of 0.875, is required to correspond to a rating of 'minimal improvement' on the CGI-I. By these criteria differences between antidepressants and placebo in randomised controlled trials, including trials conducted with people diagnosed with very severe depression, are not detectable by clinicians and fall far short of levels consistent with clinically observable minimal levels of improvement. Clinical significance should be considered alongside statistical significance when making decisions about the approval and use of medications like antidepressants.

Distinct neural representations of placebo and nocebo effects

Expectations shape the way we experience the world. In this study, we used fMRI to investigate how positive and negative expectation can change pain experiences in the same cohort of subjects. We first manipulated subjects' treatment expectation of the effectiveness of three inert creams, with one cream labeled "Lidocaine" (positive expectancy), one labeled "Capsaicin" (negative expectancy) and one labeled "Neutral" by surreptitiously decreasing, increasing, or not changing respectively, the intensity of the noxious stimuli administered following cream application. We then used fMRI to investigate the signal changes associated with administration of identical pain stimuli before and after the treatment and control creams. Twenty-four healthy adults completed the study. Results showed that expectancy significantly modulated subjective pain ratings. After controlling for changes in the neutral condition, the subjective pain rating changes evoked by positive and negative expectancies were significantly associated. fMRI results showed that the expectation of an increase in pain induced significant fMRI signal changes in the insula, orbitofrontal cortex, and periaqueductal gray, whereas the expectation of pain relief evoked significant fMRI signal changes in the striatum. No brain regions were identified as common to both "Capsaicin" and "Lidocaine" conditioning. There was also no significant association between the brain response to identical noxious stimuli in the pain matrix evoked by positive and negative expectancies. Our findings suggest that positive and negative expectancies engage different brain networks to modulate our pain experiences, but, overall, these distinct patterns of neural activation result in a correlated placebo and nocebo behavioral response.

Conscientiousness is modified by genetic variation in catechol-O-methyltransferase to reduce symptom complaints in IBS patients

BACKGROUND

Attention to and perception of physical sensations and somatic states can significantly influence reporting of complaints and symptoms in the context of clinical care and randomized trials. Although anxiety and high neuroticism are known to increase the frequency and severity of complaints, it is not known if other personality dimensions or genes associated with cognitive function or sympathetic tone can influence complaints. Genetic variation in catechol-O-methyltransferase (COMT) is associated with anxiety, personality, pain, and response to placebo treatment. We hypothesized that the association of complaint reporting with personality might be modified by variation in the COMT val158met genotype.

METHODS

We administered a standard 25-item complaint survey weekly over 3-weeks to a convenience sample of 187 irritable bowel syndrome patients enrolled in a placebo intervention trial and conducted a repeated measures analysis.

RESULTS

We found that complaint severity rating, our primary outcome, was negatively associated with the personality measures of conscientiousness (β = -0.31 SE 0.11, P = 0.003) and agreeableness (β = -0.38 SE 0.12, P = 0.002) and was positively associated with neuroticism (β = 0.24 SE 0.09, P = 0.005) and anxiety (β = 0.48 SE 0.09, P < 0.0001). We also found a significant interaction effect of COMT met alleles (β = -32.5 SE 14.1, P = 0.021). in patients genotyped for COMT val158met (N  = 87) specifically COMT × conscientiousness (β = 0.73 SE 0.26, P = 0.0042) and COMT × anxiety (β = -0.42 SE 0.16, P = 0.0078) interaction effects.

CONCLUSION

These findings potentially broaden our understanding of the factors underlying clinical complaints to include the personality dimension of conscientiousness and its modification by COMT.

Hypnosis, suggestion, and suggestibility: an integrative model

This article elucidates an integrative model of hypnosis that integrates social, cultural, cognitive, and neurophysiological variables at play both in and out of hypnosis and considers their dynamic interaction as determinants of the multifaceted experience of hypnosis. The roles of these variables are examined in the induction and suggestion stages of hypnosis, including how they are related to the experience of involuntariness, one of the hallmarks of hypnosis. It is suggested that studies of the modification of hypnotic suggestibility; cognitive flexibility; response sets and expectancies; the default-mode network; and the search for the neurophysiological correlates of hypnosis, more broadly, in conjunction with research on social psychological variables, hold much promise to further understanding of hypnosis.

A Neural Mechanism for Nonconscious Activation of Conditioned Placebo and Nocebo Responses

Fundamental aspects of human behavior operate outside of conscious awareness. Yet, theories of conditioned responses in humans, such as placebo and nocebo effects on pain, have a strong emphasis on conscious recognition of contextual cues that trigger the response. Here, we investigated the neural pathways involved in nonconscious activation of conditioned pain responses, using functional magnetic resonance imaging in healthy participants. Nonconscious compared with conscious activation of conditioned placebo analgesia was associated with increased activation of the orbitofrontal cortex, a structure with direct connections to affective brain regions and basic reward processing. During nonconscious nocebo, there was increased activation of the thalamus, amygdala, and hippocampus. In contrast to previous assumptions about conditioning in humans, our results show that conditioned pain responses can be elicited independently of conscious awareness and our results suggest a hierarchical activation of neural pathways for nonconscious and conscious conditioned responses. Demonstrating that the human brain has a nonconscious mechanism for responding to conditioned cues has major implications for the role of associative learning in behavioral medicine and psychiatry. Our results may also open up for novel approaches to translational animal-to-human research since human consciousness and animal cognition is an inherent paradox in all behavioral science.

Altered placebo and drug labeling changes the outcome of episodic migraine attacks

Information provided to patients is thought to influence placebo and drug effects. In a prospective, within-subjects, repeated-measures study of 66 subjects with episodic migraine, we investigated how variations in medication labeling modified placebo and drug effects. An initial attack with no treatment served as a control. In six subsequent migraine attacks, each participant received either placebo or Maxalt (10-mg rizatriptan) administered under three information conditions ranging from negative to neutral to positive (told placebo, told Maxalt or placebo, told Maxalt) (N = 459 documented attacks). Treatment order was randomized. Maxalt was superior to placebo for pain relief. When participants were given placebo labeled as (i) placebo, (ii) Maxalt or placebo, and (iii) Maxalt, the placebo effect increased progressively. Maxalt had a similar progressive boost when labeled with these three labels. The efficacies of Maxalt labeled as placebo and placebo labeled as Maxalt were similar. The efficacy of open-label placebo was superior to that of no treatment. Relative to no treatment, the placebo, under each information condition, accounted for more than 50% of the drug effect. Increasing "positive" information incrementally boosted the efficacy of both placebo and medication during migraine attacks. The benefits of placebo persisted even if placebo was honestly described. Whether treatment involves medication or placebo, the information provided to patients and the ritual of pill taking are important components of care.

Well-loved music robustly relieves pain: a randomized, controlled trial

Music has pain-relieving effects, but its mechanisms remain unclear. We sought to verify previously studied analgesic components and further elucidate the underpinnings of music analgesia. Using a well-characterized conditioning-enhanced placebo model, we examined whether boosting expectations would enhance or interfere with analgesia from strongly preferred music. A two-session experiment was performed with 48 healthy, pain experiment-naïve participants. In a first cohort, 36 were randomized into 3 treatment groups, including music enhanced with positive expectancy, non-musical sound enhanced with positive expectancy, and no expectancy enhancement. A separate replication cohort of 12 participants received only expectancy-enhanced music following the main experiment to verify the results of expectancy-manipulation on music. Primary outcome measures included the change in subjective pain ratings to calibrated experimental noxious heat stimuli, as well as changes in treatment expectations. Without conditioning, expectations were strongly in favor of music compared to non-musical sound. While measured expectations were enhanced by conditioning, this failed to affect either music or sound analgesia significantly. Strongly preferred music on its own was as pain relieving as conditioning-enhanced strongly preferred music, and more analgesic than enhanced sound. Our results demonstrate the pain-relieving power of personal music even over enhanced expectations.

TRIAL INFORMATION

Clinicaltrials.gov NCT01835275.

Polymorphisms in catechol-O-methyltransferase modify treatment effects of aspirin on risk of cardiovascular disease

OBJECTIVE

Catechol-O-methyltransferase (COMT), a key enzyme in catecholamine metabolism, is implicated in cardiovascular, sympathetic, and endocrine pathways. This study aimed to confirm preliminary association of COMT genetic variation with incident cardiovascular disease (CVD). It further aimed to evaluate whether aspirin, a commonly used CVD prevention agent, modified the potential association of COMT with incident CVD.

APPROACH AND RESULTS

We examined COMT polymorphism rs4680 (MAF [minor allele frequency], 0.47), encoding a nonsynonymous methionine-to-valine substitution, in the Women's Genome Health Study (WGHS), a large population-based cohort of women with randomized allocation to aspirin or vitamin E when compared with placebo and 10-year follow-up. Rs4680 effects were confirmed with COMT polymorphism rs4818 and also examined in Coronary ARtery DIsease Genome-wide Replication and Meta-analysis/The Coronary Artery Disease Genetics Consortium, consortia for genome-wide association studies of coronary artery disease. Among WGHS women allocated to placebo (135 events/n=5811), the rs4680 valine allele was protective against incident CVD relative to the methionine (hazard ratio [HR; 95% confidence interval {CI}], 0.66 [0.51-0.84]; P=0.0007); an association also observed in Coronary ARtery DIsease Genome-wide Replication and Meta-analysis and The Coronary Artery Disease Genetics Consortium (combined P=2.4×10(-5)). In the WGHS, the rs4680 association was abolished by randomized allocation to aspirin, such that valine/valine women experienced higher CVD rates with aspirin allocation when compared with placebo (HR [95% CI], 1.85 [1.05-3.25]; P=0.033), whereas methionine/methionine women experienced lower rates (HR [95% CI], 0.60 [0.39-0.93]; P=0.023). Allocation to vitamin E also conferred higher but nonsignificant CVD rates on valine/valine (HR [95% CI], 1.50 [0.83-2.70]; P=0.180) when compared with significantly lower rates on methionine/methionine (HR [95% CI], 0.53 [0.34-0.84]; P=0.006) women. Rs4818 results were similar.

CONCLUSIONS

Common COMT polymorphisms were associated with incident CVD, and this association was modified by randomized allocation to aspirin or vitamin E. Replication of these findings is required.

The efficacy of paroxetine and placebo in treating anxiety and depression: a meta-analysis of change on the Hamilton Rating Scales

BACKGROUND

Previous meta-analyses of published and unpublished trials indicate that antidepressants provide modest benefits compared to placebo in the treatment of depression; some have argued that these benefits are not clinically significant. However, these meta-analyses were based only on trials submitted for the initial FDA approval of the medication and were limited to those aimed at treating depression. Here, for the first time, we assess the efficacy of a selective serotonin reuptake inhibitor (SSRI) in the treatment of both anxiety and depression, using a complete data set of all published and unpublished trials sponsored by the manufacturer.

METHODS AND FINDINGS

GlaxoSmithKline has been required to post the results for all sponsored clinical trials online, providing an opportunity to assess the efficacy of an SSRI (paroxetine) with a complete data set of all trials conducted. We examined the data from all placebo-controlled, double-blind trials of paroxetine that included change scores on the Hamilton Rating Scale for Anxiety (HRSA) and/or the Hamilton Rating Scale for Depression (HRSD). For the treatment of anxiety (k = 12), the efficacy difference between paroxetine and placebo was modest (d = 0.27), and independent of baseline severity of anxiety. Overall change in placebo-treated individuals replicated 79% of the magnitude of paroxetine response. Efficacy was superior for the treatment of panic disorder (d = 0.36) than for generalized anxiety disorder (d = 0.20). Published trials showed significantly larger drug-placebo differences than unpublished trials (d's = 0.32 and 0.17, respectively). In depression trials (k = 27), the benefit of paroxetine over placebo was consistent with previous meta-analyses of antidepressant efficacy (d = 0.32).

CONCLUSIONS

The available empirical evidence indicates that paroxetine provides only a modest advantage over placebo in treatment of anxiety and depression. Treatment implications are discussed.

Sharing pain and relief: neural correlates of physicians during treatment of patients

Patient-physician interactions significantly contribute to placebo effects and clinical outcomes. While the neural correlates of placebo responses have been studied in patients, the neurobiology of the clinician during treatment is unknown. This study investigated physicians' brain activations during patient-physician interaction while the patient was experiencing pain, including a 'treatment', 'no-treatment' and 'control' condition. Here, we demonstrate that physicians activated brain regions previously implicated in expectancy for pain-relief and increased attention during treatment of patients, including the right ventrolateral and dorsolateral prefrontal cortices. The physician's ability to take the patients' perspective correlated with increased brain activations in the rostral anterior cingulate cortex, a region that has been associated with processing of reward and subjective value. We suggest that physician treatment involves neural representations of treatment expectation, reward processing and empathy, paired with increased activation in attention-related structures. Our findings further the understanding of the neural representations associated with reciprocal interactions between clinicians and patients; a hallmark for successful treatment outcomes.

Antidepressants and the Placebo Effect

Antidepressants are supposed to work by fixing a chemical imbalance, specifically, a lack of serotonin in the brain. Indeed, their supposed effectiveness is the primary evidence for the chemical imbalance theory. But analyses of the published data and the unpublished data that were hidden by drug companies reveals that most (if not all) of the benefits are due to the placebo effect. Some antidepressants increase serotonin levels, some decrease it, and some have no effect at all on serotonin. Nevertheless, they all show the same therapeutic benefit. Even the small statistical difference between antidepressants and placebos may be an enhanced placebo effect, due to the fact that most patients and doctors in clinical trials successfully break blind. The serotonin theory is as close as any theory in the history of science to having been proved wrong. Instead of curing depression, popular antidepressants may induce a biological vulnerability making people more likely to become depressed in the future.

Expectancy and Conditioning in Placebo Analgesia: Separate or Connected Processes?

Expectancy and conditioning are often tested as opposing explanations of placebo analgesia, most commonly by pitting the effects of a conditioning procedure against those of a verbally-induced expectation for pain reduction. However, conditioning procedures can also alter expectations, such that the effect of conditioning on pain might be mediated by expectancy. We assessed the effect of conditioning on expected pain and placebo-induced pain reduction. Participants were told that the treatment (real or sham acupuncture) would affect one side of the arm but not the other. Because a real acupuncture effect would not be specific to a randomly selected side of the arm, any difference in pain between the "treated" and the "untreated" side would be a placebo effect. There were no significant main effects or interactions associated with type of acupuncture (real versus sham). In both groups, conditioning decreased expected pain for "treated" location and also increased the placebo effect (i.e., the difference in pain report between "treated" and "untreated" locations). In addition, mediation analysis lent support to the hypothesis that the effects of conditioning on placebo analgesia may be mediated by expectancy, although the size of this indirect effect requires further study.