Placebo effects mediated by endogenous opioid activity on mu-opioid receptors

The role of endogenous opioids in mindfulness and sham mindfulness-meditation for the direct alleviation of evoked chronic low back pain: a randomized clinical trial

Chronic low back pain (cLBP) is the most prevalent chronic pain condition. There are no treatments that haven been found to directly assuage evoked cLBP. To this extent, mindfulness-meditation is a promising pain therapy. Yet, it is unclear if meditation can be utilized to directly attenuate evoked chronic pain through endogenous opioids. A double-blind, randomized, and placebo-controlled clinical trial with a drug crossover design examined if mindfulness-meditation, as compared to sham mindfulness-meditation, attenuated straight leg-raise test evoked chronic pain during intravenous (0.15 mg/kg bolus + 0.15 mg/kg/hour maintenance) naloxone (opioid antagonist) and placebo-saline infusion. Fifty-nine individuals with cLBP (mean age = 46 years; 30 females) completed all study procedures. After the pre-intervention pain testing session, patients were randomized to a four-session (20-min/session) mindfulness (n = 30) or sham mindfulness-meditation (n = 29) intervention. After the interventions, mindfulness and sham mindfulness-meditation were associated with significant reductions in back pain during saline and naloxone infusion when compared to rest (non-meditation) in response to the cLBP-evoking straight leg-raise test. These results indicate that meditation directly reduces evoked chronic pain through non-opioidergic processes. Importantly, after the interventions, the mindfulness group reported significantly lower straight leg-raise induced pain than the sham mindfulness-meditation group during rest (non-meditation) and meditation. Mindfulness and sham mindfulness-meditation training was also associated with significantly lower Brief Pain Inventory severity and interference scores. The pain-relieving effects of mindfulness meditation were more pronounced than a robust sham-mindfulness meditation intervention, suggesting that non-reactive appraisal processes may be uniquely associated with improvements in chronic low-back pain.Trial Registration: ClinicalTrials.gov identifier: NCT04034004.

Neuropsychological mechanisms of observational learning in human placebo effects

Scientific evidence indicates that placebo effects are psychoneurobiological events involving the contribution of distinct central nervous systems and peripheral physiological mechanisms that influence pain perception and other symptoms. Placebo effects can occur without formal conditioning and direct prior experience because crucial information can be acquired through observational learning. Observation of benefits in another person results in placebo effects of a magnitude like those induced by directly experiencing an analgesic benefit. Understanding the psychological mechanisms of observationally induced placebo effects is a complex and multifaceted endeavor. While previous reviews have highlighted various frameworks and models to understand these phenomena, the underlying biological mechanisms have been overlooked. We summarize critically current understanding of its behavioral and neural mechanisms. Understanding the neural mechanisms of hypoalgesia driven by observation can serve as a foundation for future development of novel theoretical and methodological approaches and ultimately, applications.

Expectancy Effects in Psychedelic Trials

Clinical trials of psychedelic compounds like psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltrptamine (DMT) have forced a reconsideration of how nondrug factors, such as participant expectations, are measured and controlled in mental health research. As doses of these profoundly psychoactive substances increase, so does the difficulty in concealing the treatment condition in the classic double-blind, placebo-controlled trial design. As widespread public enthusiasm for the promise of psychedelic therapy grows, so do questions regarding whether and how much trial results are biased by positive expectancy. First, we review the key concepts related to expectancy and its measurement. Then, we review expectancy effects that have been reported in both micro- and macrodose psychedelic trials from the modern era. Finally, we consider expectancy as a discrete physiological process that can be independent of, or even interact with, the drug effect. Expectancy effects can be harnessed to improve treatment outcomes and can also be actively managed in controlled studies to enhance the rigor and generalizability of future psychedelic trials.

Clinical Phenotypes Supporting the Relationship Between Sleep Disturbance and Impairment of Placebo Effects

Lack of good sleep or insomnia can lead to many health issues, including an elevated risk of cardiovascular disease, obesity, fatigue, low mood, and pain. While chronic pain negatively impacts sleep quality, the relationship between descending pain modulatory systems like placebo effects and sleep quality is not thoroughly known. We addressed this aspect in a cross-sectional study in participants with chronic pain. Placebo effects were elicited in a laboratory setting using thermal heat stimulations delivered with visual cues using classical conditioning and verbal suggestions. We estimated the levels of insomnia severity with the Insomnia Severity Index and the sleep quality with the Pittsburg Sleep Quality Index. The previous night's sleep continuity was assessed as total sleep time, sleep efficiency, and sleep midpoint the night before the experiment. 277 people with chronic pain and 189 pain-free control individuals participated. Participants with chronic pain and insomnia showed smaller placebo effects than those with chronic pain without insomnia. Similarly, poor sleep quality was associated with reduced placebo effects among participants with chronic pain. Clinical anxiety measured by Depression Anxiety Stress Scales partially mediated these effects. In contrast, placebo effects were not influenced by the presence of insomnia or poor sleep quality in pain-free participants. Sleep continuity the night before the experiment did not influence the placebo effects. Our results indicate that participants who experience insomnia and/or poor sleep quality and chronic pain have smaller placebo effects, and that the previous night sleep continuity does not influence the magnitude of placebo effects. PERSPECTIVE: This study examined the relationship between sleep disturbances and experimentally induced placebo effects. We found that individuals with chronic pain who experience insomnia and poor sleep quality demonstrated reduced placebo effects compared to their counterparts with good sleep quality and no insomnia.

Does Active Inference Provide a Comprehensive Theory of Placebo Analgesia?

Placebo interventions generate mismatches between expected pain and sensory signals from which pain states are inferred. Because we lack direct access to bodily states, we can only infer whether nociceptive activity indicates tissue damage or results from noise in sensory channels. Predictive processing models propose to make optimal inferences using prior knowledge given noisy sensory data. However, these models do not provide a satisfactory explanation of how pain relief expectations are translated into physiological manifestations of placebo responses. Furthermore, they do not account for individual differences in the ability to endogenously regulate nociceptive activity in predicting placebo analgesia. The brain not only passively integrates prior pain expectations with nociceptive activity to infer pain states (perceptual inference) but also initiates various types of actions to ensure that sensory data are consistent with prior pain expectations (active inference). We argue that depending on whether the brain interprets conflicting sensory data (prediction errors) as a signal to learn from or noise to be attenuated, the brain initiates opposing types of action to facilitate learning from sensory data or, conversely, to enhance the biasing influence of prior pain expectations on pain perception. Furthermore, we discuss the role of stress, anxiety, and unpredictability of pain in influencing the weighting of prior pain expectations and sensory data and how they relate to the individual ability to regulate nociceptive activity (endogenous pain modulation). Finally, we provide suggestions for future studies to test the implications of the active inference model of placebo analgesia.

Resolving the Delusion Paradox

BACKGROUND AND HYPOTHESIS

The neurocomputational framework of predictive processing (PP) provides a promising approach to explaining delusions, a key symptom of psychotic disorders. According to PP, the brain makes inferences about the world by weighing prior beliefs against the available sensory data. Mismatches between prior beliefs and sensory data result in prediction errors that may update the brain's model of the world. Psychosis has been associated with reduced weighting of priors relative to the sensory data. However, delusional beliefs are highly resistant to change, suggesting increased rather than decreased weighting of priors. We propose that this "delusion paradox" can be resolved within a hierarchical PP model: Reduced weighting of prior beliefs at low hierarchical levels may be compensated by an increased influence of higher-order beliefs represented at high hierarchical levels, including delusional beliefs. This may sculpt perceptual processing into conformity with delusions and foster their resistance to contradictory evidence.

STUDY DESIGN

We review several lines of experimental evidence on low- and high-level processes, and their neurocognitive underpinnings in delusion-related phenotypes and link them to predicted processing.

STUDY RESULTS

The reviewed evidence supports the notion of decreased weighting of low-level priors and increased weighting of high-level priors, in both delusional and delusion-prone individuals. Moreover, we highlight the role of prefrontal cortex as a neural basis for the increased weighting of high-level prior beliefs and discuss possible clinical implications of the proposed hierarchical predictive-processing model.

CONCLUSIONS

Our review suggests the delusion paradox can be resolved within a hierarchical PP model.

How Do Expectations Modulate Pain? A Motivational Perspective

Expectations can profoundly modulate pain experience, during which the periaqueductal gray (PAG) plays a pivotal role. In this article, we focus on motivationally evoked neural activations in cortical and brainstem regions both before and during stimulus administration, as has been demonstrated by experimental studies on pain-modulatory effects of expectations, in the hope of unraveling how the PAG is involved in descending and ascending nociceptive processes. This motivational perspective on expectancy effects on the perception of noxious stimuli sheds new light on psychological and neuronal substrates of pain and its modulation, thus having important research and clinical implications.

The Placebo Effect in Psychosis: Why It Matters and How to Measure It

Psychosis is characterized by unusual percepts and beliefs in the form of hallucinations and delusions. Antipsychotic medication, the primary treatment for psychosis, is often ineffective and accompanied by severe side effects, but research has not identified an effective alternative in several decades. One reason that clinical trials fail is that patients with psychosis tend to show a significant therapeutic response to inert control treatments, known as the placebo effect, which makes it difficult to distinguish drug effects from placebo effects. Conversely, in clinical practice, a strong placebo effect may be useful because it could enhance the overall treatment response. Identifying factors that predict large placebo effects could improve the future outlook of psychosis treatment. Biomarkers of the placebo effect have already been suggested in pain and depression, but not in psychosis. Quantifying markers of the placebo effect would have the potential to predict placebo effects in psychosis clinical trials. Furthermore, the placebo effect and psychosis may represent a shared neurocognitive mechanism in which prior beliefs are weighted against new sensory information to make inferences about reality. Examining this overlap could reveal new insights into the mechanisms underlying psychosis and indicate novel treatment targets. We provide a narrative review of the importance of the placebo effect in psychosis and propose a novel method to assess it.

Placebo treatment affects brain systems related to affective and cognitive processes, but not nociceptive pain

Placebo analgesia is a replicable and well-studied phenomenon, yet it remains unclear to what degree it includes modulation of nociceptive processes. Some studies find effects consistent with nociceptive effects, but meta-analyses show that these effects are often small. We analyzed placebo analgesia in a large fMRI study (N = 392), including placebo effects on brain responses to noxious stimuli. Placebo treatment caused robust analgesia in both conditioned thermal and unconditioned mechanical pain. Placebo did not decrease fMRI activity in nociceptive pain regions, including the Neurologic Pain Signature (NPS) and pre-registered spinothalamic pathway regions, with strong support from Bayes Factor analyses. However, placebo treatment affected activity in pre-registered analyses of a second neuromarker, the Stimulus Intensity Independent Pain Signature (SIIPS), and several associated a priori brain regions related to motivation and value, in both thermal and mechanical pain. Individual differences in behavioral analgesia were correlated with neural changes in both thermal and mechanical pain. Our results indicate that processes related to affective and cognitive aspects of pain primarily drive placebo analgesia.

A novel lotion formulation of 20% oxybutynin hydrochloride for the treatment of primary palmar hyperhidrosis: A randomized, placebo-controlled, double-blind, phase III study

BACKGROUND

No previous controlled studies have been specifically designed or adequately powered to show the efficacy of topical oxybutynin for palmar hyperhidrosis by using quantitative measures.

OBJECTIVE

To evaluate efficacy of 20% oxybutynin hydrochloride lotion (20% OL) in reducing palmar sweat volume in patients with primary palmar hyperhidrosis (PPHH).

METHODS

In a randomized controlled trial, Japanese patients with PPHH aged 12 years and older received either 20% OL (n = 144) or placebo (n = 140) on both palms once daily for 4 weeks. Palmar sweat volume was measured by the ventilated capsule method. For the primary outcome, response was defined as a reduction of sweat volume of at least 50% from baseline.

RESULTS

At week 4, the responder rate for sweat volume was significantly higher in the 20% OL arm than in the placebo arm (52.8% vs 24.3%, respectively; treatment difference, 28.5% [95% CI, 17.7% to 39.3%]; P < .001). No serious adverse events occurred, and no adverse events led to treatment discontinuation.

LIMITATIONS

The treatment period was only 4 weeks.

CONCLUSIONS

In patients with PPHH, 20% OL is superior to placebo in reducing palmar sweat volume.

The Effect of Positive Therapeutic Communication on Pain (POPAIN) and Anxiety During Arterial Blood Gas Standardized Procedures in the Emergency Department Compared to Traditional Communication: Protocol for a Monocentric Randomized Controlled Trial

BACKGROUND

In the emergency department (ED), medical procedures, such as arterial blood gas (ABG) testing, can cause pain and high stress levels. However, ABG testing is a routine procedure assessing the severity of the patient's condition. To reduce the pain of ABG, several methods have been investigated without significant difference in pain perception. Communication, a key element of care, has shown a significant effect on pain perception. A positive communication strategy, including positive, kind, or reassuring words, can reduce pain perception, while negative words can raise this perception, causing discomfort, known as the "nocebo effect." Although some studies have compared the impact of verbal attitudes, particularly in anesthesia and mainly with staff already trained in hypnosis, to the best of our knowledge, none have investigated the effect of communication in the emergency setting, where patients may be more suggestible to the words used.

OBJECTIVE

In this study, we will investigate the effect of positive therapeutic communication on pain, anxiety, discomfort, and global satisfaction in patients requiring ABG compared to nocebo and neutral communication.

METHODS

A single-center, double-blind randomized controlled trial (RCT) with 3 parallel arms will be conducted with 249 patients requiring ABG during their ED visit. Patients will be randomly assigned to 1 of 3 groups before receiving ABG: positive communication group, negative communication (nocebo) group, or neutral communication (neutral) group. The communication and the words used by the physicians during hygiene preparation, artery location, and puncture will be imposed in each group. The study will be proposed to each patient corresponding to the inclusion criteria. The physicians will not be trained in hypnosis or in positive therapeutic communication. The procedure will be recorded with audio recorders to test its quality. Intention-to-treat analysis will be performed. The primary endpoint is the onset of pain. The secondary outcomes are patient comfort, patient anxiety, and global satisfaction of the patient with the communication strategy used.

RESULTS

On average, 2000 ABG procedures are performed each year in the EDs of hospitals. In this study, 249 patients are expected to be included. With a projected positive response rate of 80%, we intend to include 25 (10%) patients per month. The inclusion period began in April 2023 and will run until July 2024. We hope to publish the results of the study during the fall of 2024.

CONCLUSIONS

To the best of our knowledge, this study is the first RCT assessing the use of positive communication on pain and anxiety in patients undergoing the ABG procedure in the ED. A reduction in pain, discomfort, and anxiety is expected when using positive communication. If the results are positive, this could be useful to the medical community and encourage clinicians to monitor their communication during care.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05434169; https://clinicaltrials.gov/ct2/show/NCT05434169.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/42043.

Altered resting-state brain activity in functional dyspepsia patients: a coordinate-based meta-analysis

Background

Neuroimaging studies have identified aberrant activity patterns in multiple brain regions in functional dyspepsia (FD) patients. However, due to the differences in study design, these previous findings are inconsistent, and the underlying neuropathological characteristics of FD remain unclear.

Methods

Eight databases were systematically searched for literature from inception to October 2022 with the keywords "Functional dyspepsia" and "Neuroimaging." Thereafter, the anisotropic effect size signed the differential mapping (AES-SDM) approach that was applied to meta-analyze the aberrant brain activity pattern of FD patients.

Results

A total of 11 articles with 260 FD patients and 202 healthy controls (HCs) were included. The AES-SDM meta-analysis demonstrated that FD patients manifested increased activity in the bilateral insula, left anterior cingulate gyrus, bilateral thalamus, right precentral gyrus, left supplementary motor area, right putamen, and left rectus gyrus and decreased functional activity in the right cerebellum compared to the HCs. Sensitivity analysis showed that all these above regions were highly reproducible, and no significant publication bias was detected.

Conclusion

The current study demonstrated that FD patients had significantly abnormal activity patterns in several brain regions involved in visceral sensation perception, pain modulation, and emotion regulation, which provided an integrated insight into the neuropathological characteristics of FD.

Study on brain function of the frontal lobe in patients with functional gastroduodenal disease by near-infrared functional imaging

OBJECTIVE

functional gastroduodenal disease is the main type of functional gastrointestinal disease in the clinical department of Gastroenterology and psychosomatic medicine at present, which accounts for a large proportion of outpatients in gastroenterology. The main manifestations are epigastric pain, dyspepsia, belching, chronic nausea, and vomiting. The purpose of this study is to explore the changes in brain function in patients with functional gastroduodenal diseases through experiments to reveal the possible central etiology and development process.

METHODS

the functional changes of the prefrontal lobe in patients with functional gastroduodenal diseases and normal controls were detected and analyzed by near-infrared brain imaging. At the same time, SCL-90 was used to evaluate the mental health status of patients with functional gastroduodenal diseases and normal controls. The changes in the autonomic nerve system in patients and normal controls were detected and compared by heart rate variability trend chart.

RESULTS

the activity of left prefrontal lobe areas s8-d8, s10-d4, s10-d10 and s10-d15 in patients with functional gastroduodenal disease was significantly lower than normal controls (p < 0.05). The SCL-90 scale showed that there were significant differences between patients with functional gastroduodenal disease and normal controls, especially in depression, compulsion, anxiety, somatization, interpersonal sensitivity and hostility (p < 0.05). There was no significant difference in lf/hf values detected by the HRV trend chart (p > 0.05).

CONCLUSION

the function of the left frontal lobe is decreased in patients with functional gastroduodenal disease. The autonomic nervous system may be related to the connection system between the brain center and internal organs.

Management of Episodic Migraine with Neuromodulation: A Case Report

Migraine is a highly prevalent neurovascular disorder that affects approximately 15% of the global population. Migraine attacks are a complex cascade of neurologic events that lead to debilitating symptoms and are often associated with inhibitory behavior. The constellation of severe signs and symptoms during the ictal phase (headache attack) makes migraine the third most common cause of disability globally in both sexes under the age of 50. Misuse of pharmaceuticals, such as opiates, can lead to devastating outcomes and exacerbation of pain and headache attacks. A safe and well-tolerated non-pharmacological research approach is high-definition transcranial direct current stimulation over the M1.

Placebo and nocebo effects: from observation to harnessing and clinical application

Placebo and nocebo effects are salubrious benefits and negative outcomes attributable to non-specific symbolic components. Leveraging advanced experimental and analytical approaches, recent studies have elucidated complicated neural mechanisms that may serve as a solid basis for harnessing the powerful self-healing and self-harming capacities and applying these findings to improve medical practice and minimize the unintended exacerbation of symptoms in medical practice. We review advances in employing psychosocial, pharmacological, and neuromodulation approaches to modulate/harness placebo and nocebo effects. While these approaches show promising potential, translating these research findings into clinical settings still requires careful methodological, technical, and ethical considerations.

Is Electrical Stimulation Effective in Preventing or Treating Delayed-onset Muscle Soreness (DOMS) in Athletes and Untrained Adults? A Systematic Review With Meta-Analysis

The effectiveness of electrical stimulation (ES) in preventing or treating delayed-onset muscle soreness (DOMS) and its effects on muscle recovery is unclear. The systematic review investigated the benefits or harms of ES on DOMS and muscle recovery. Databases (PubMed, Medline, CENTRAL, EMBASE, CINAHL, PsycINFO, PEDro, LILACS, SPORTDiscus) were searched up to March, 31st 2021 for randomized controlled trials (RCTs) of athletes or untrained adults with DOMS treated with ES and compared to placebo/sham (simulation or without ES), or control (no intervention). Data were pooled in a meta-analysis. Risk of bias (Cochrane Collaboration tool) and quality of evidence (GRADE) were analyzed. Fourteen trials (n=435) were included in this review and 12 trials (n=389) were pooled in a meta-analysis. Evidence of very low to low quality indicates that ES does not prevent or treat DOMS as well as ES does not help to promote muscle recovery immediately, 24, 48, 72, 96 hours after the intervention. Only one study monitored adverse events. There are no recommendations that support the use of ES in DOMS and muscle recovery. PERSPECTIVES: No recommendations support the use of electrical stimulation in delayed-onset muscle soreness and muscle recovery in athletes and untrained adults. This means that electrical stimulation is not fruitful for this population according those protocols used. Therefore, unlikely that further randomized controlled trials with the same approach will yield promising results.

Instructions and experiential learning have similar impacts on pain and pain-related brain responses but produce dissociations in value-based reversal learning

Recent data suggest that interactions between systems involved in higher order knowledge and associative learning drive responses during value-based learning. However, it is unknown how these systems impact subjective responses, such as pain. We tested how instructions and reversal learning influence pain and pain-evoked brain activation. Healthy volunteers (n=40) were either instructed about contingencies between cues and aversive outcomes or learned through experience in a paradigm where contingencies reversed three times. We measured predictive cue effects on pain and heat-evoked brain responses using functional magnetic resonance imaging. Predictive cues dynamically modulated pain perception as contingencies changed, regardless of whether participants received contingency instructions. Heat-evoked responses in the insula, anterior cingulate, and other regions updated as contingencies changed, and responses in the prefrontal cortex mediated dynamic cue effects on pain, whereas responses in the brainstem’s rostroventral medulla (RVM) were shaped by initial contingencies throughout the task. Quantitative modeling revealed that expected value was shaped purely by instructions in the Instructed Group, whereas expected value updated dynamically in the Uninstructed Group as a function of error-based learning. These differences were accompanied by dissociations in the neural correlates of value-based learning in the rostral anterior cingulate, thalamus, and posterior insula, among other regions. These results show how predictions dynamically impact subjective pain. Moreover, imaging data delineate three types of networks involved in pain generation and value-based learning: those that respond to initial contingencies, those that update dynamically during feedback-driven learning as contingencies change, and those that are sensitive to instruction. Together, these findings provide multiple points of entry for therapies designs to impact pain.

Placebo Analgesia Reduces Costly Prosocial Helping to Lower Another Person's Pain

Painkiller administration lowers pain empathy, but whether this also reduces prosocial behavior is unknown. In this preregistered study, we investigated whether inducing analgesia through a placebo painkiller reduced effortful helping. When given the opportunity to reduce the pain of another person, individuals experiencing placebo analgesia (n = 45 adults from Austria; 21 male, 24 female) made fewer prosocial choices at the lowest helping level and exerted less physical effort when helping, compared with controls whose pain sensitivity was unaltered (n = 45; 21 male, 24 female). Self-reported empathic unpleasantness positively correlated with prosocial choices across the whole sample. While not replicating group differences in empathy, a mediation analysis revealed that the level of unpleasantness to other people's pain fully mediated the effect of placebo analgesia on prosocial choices. Given the importance of prosociality for social cohesion, these findings have broad potential implications both for individuals under the influence of painkillers and for society at large.

Unique and joint associations of polygenic risk for major depression and opioid use disorder with endogenous opioid system function

Major depressive disorder (MDD) and opioid use disorder (OUD) are common, potentially fatal, polygenic disorders that are moderately heritable and often co-occur. We examined the unique and shared associations of polygenic risk scores (PRS) for these disorders with µ-opioid receptor (MOR) concentration and endogenous opioid response during a stressful stimulus. Participants were 144 healthy European-ancestry (EA) subjects (88 females) who underwent MOR quantification scans with [11C]carfentanil and PET and provided DNA for genotyping. MOR non-displaceable binding potential (BPND) was measured in 5 regions of interest (ROIs) related to mood and addiction. We examined associations of PRS both at baseline and following opioid release calculated as the ratio of baseline and stress-challenge scans, first in the entire sample and then separately by sex. MOR availability at baseline was positively associated with MDD PRS in the amygdala and ventral pallidum. MDD and OUD PRS were significantly associated with stress-induced opioid system activation in multiple ROIs, accounting for up to 14.5% and 5.4%, respectively, of the variance in regional activation. The associations were most robust among females, where combined they accounted for up to 25.0% of the variance among the ROIs. We conclude that there is a pathophysiologic link between polygenic risk for MDD and OUD and opioid system activity, as evidenced by PRS with unique and overlapping regional associations with this neurotransmitter system. This link could help to explain the high rate of comorbidity of MDD and OUD and suggests that opioid-modulating interventions could be useful in treating MDD and OUD, both individually and jointly.

Functional brain mapping in patients with chronic back pain shows age-related differences

ABSTRACT

Low back pain is the most common pain condition and cause for disability in older adults. Older adults suffering from low back pain are more disabled than their healthy peers, are more predisposed to frailty, and tend to be undertreated. The cause of increased prevalence and severity of this chronic pain condition in older adults is unknown. Here, we draw on accumulating data demonstrating a critical role for brain limbic and sensory circuitries in the emergence and experience of chronic low back pain (CLBP) and the availability of resting-state brain activity data collected at different sites to study how brain activity patterns predictive of CLBP differ between age groups. We apply a data-driven multivariate searchlight analysis to amplitude of low-frequency fluctuation brain maps to classify patients with CLBP with >70% accuracy. We observe that the brain activity pattern including the paracingulate gyrus, insula/secondary somatosensory area, inferior frontal, temporal, and fusiform gyrus predicted CLBP. When separated by age groups, brain patterns predictive of older patients with CLBP showed extensive involvement of limbic brain areas including the ventromedial prefrontal cortex, the nucleus accumbens, and hippocampus, whereas only anterior insula paracingulate and fusiform gyrus predicted CLBP in the younger patients. In addition, we validated the relationships between back pain intensity ratings and CLBP brain activity patterns in an independent data set not included in our initial patterns' identification. Our results are the first to directly address how aging affects the neural signature of CLBP and point to an increased role of limbic brain areas in older patients with CLBP.

The Opioid System in Depression

Opioid receptors are widely distributed throughout the brain and play an essential role in modulating aspects of human mood, reward, and well-being. Accumulating evidence indicates the endogenous opioid system is dysregulated in depression and that pharmacological modulators of mu, delta, and kappa opioid receptors hold potential for the treatment of depression. Here we review animal and clinical data, highlighting evidence to support: dysregulation of the opioid system in depression, evidence for opioidergic modulation of behavioural processes and brain regions associated with depression, and evidence for opioidergic modulation in antidepressant responses. We evaluate clinical trials that have examined the safety and efficacy of opioidergic agents in depression and consider how the opioid system may be involved in the effects of other treatments, including ketamine, that are currently understood to exert antidepressant effects through non-opioidergic actions. Finally, we explore key neurochemical and molecular mechanisms underlying the potential therapeutic effects of opioid system engagement, that together provides a rationale for further investigation into this relevant target in the treatment of depression.

Oxytocin and the social facilitation of placebo effects

Significant clinical improvement is often observed in patients who receive placebo treatment in randomized double-blind placebo-controlled trials. While a proportion of this "improvement" reflects experimental design limitations (e.g., reliance on subjective outcomes, unbalanced groups, reporting biases), some of it reflects genuine improvement corroborated by physiological change. Converging evidence across diverse medical conditions suggests that clinically-relevant benefits from placebo treatment are associated with the activation of brain reward circuits. In parallel, evidence has accumulated showing that such benefits are facilitated by clinicians that demonstrate warmth and proficiency during interactions with patients. Here, we integrate research on these neural and social aspects of placebo effects with evidence linking oxytocin and social reward to advance a neurobiological account for the social facilitation of placebo effects. This account frames oxytocin as a key mediator of treatment success across a wide-spectrum of interventions that increase social connectedness, thereby providing a biological basis for assessing this fundamental non-specific element of medical care.

[Neurobiological and neurochemical mechanisms of placebo analgesia]

BACKGROUND

The efficacy of pain therapies can be substantially modulated by treatment expectations, which is reflected by the substantial placebo effects observed in pain (so called placebo analgesia).

QUESTION

What is currently known about the neurobiological and neurochemical mechanisms underlying placebo analgesia?

MATERIALS AND METHODS

A focused presentation of key publications in the field embedded in a structured overview of the mechanistic concepts and current theories according to recent evidence.

RESULTS

Experimental studies with functional neuroimaging showed that the effect of placebo analgesia is reflected by changes in brain activity related to pain processing and cognitive control. The important neurotransmitters involved include opioids and dopamine.

CONCLUSION

Placebo analgesia is associated with complex neurobiological and -physiological mechanisms. An advanced comprehension of these processes should be applied to optimize existing and future therapeutic approaches in pain therapy.

Hippocampus mediates nocebo impairment of opioid analgesia through changes in functional connectivity

The neural mechanisms underlying placebo analgesia have attracted considerable attention over the recent years. In contrast, little is known about the neural underpinnings of a nocebo-induced increase in pain. We previously showed that nocebo-induced hyperalgesia is accompanied by increased activity in the hippocampus that scaled with the perceived level of anxiety. As a key node of the neural circuitry of perceived threat and fear, the hippocampus has recently been proposed to coordinate defensive behaviour in a context-dependent manner. Such a role requires close interactions with other regions involved in the detection of and responses to threat. Here, we investigated the functional connectivity of the hippocampus during nocebo-induced hyperalgesia. Our results show an increase in functional connectivity between hippocampus and brain regions implicated in the processing of sensory-discriminative aspects of pain (posterior insula and primary somatosensory/motor cortex) as well as the periaqueductal gray (PAG). This nocebo-induced increase in connectivity scaled with an individual's increase in anxiety. Moreover, hippocampus connectivity with the amygdala was negatively correlated with the pain intensity reported during nocebo hyperalgesia relative to the placebo condition. Our findings suggest that the hippocampus links nocebo-induced anxiety to a heightened responsiveness to nociceptive input through changes in its crosstalk with pain-modulatory brain areas.

Understanding Pain and Trauma Symptoms in Veterans From Resting-State Connectivity: Unsupervised Modeling

Trauma and posttraumatic stress are highly comorbid with chronic pain and are often antecedents to developing chronic pain conditions. Pain and trauma are associated with greater utilization of medical services, greater use of psychiatric medication, and increased total cost of treatment. Despite the high overlap in the clinic, the neural mechanisms of pain and trauma are often studied separately. In this study, resting-state functional magnetic resonance imaging (rs-fMRI) scans were completed among a diagnostically heterogeneous sample of veterans with a range of back pain and trauma symptoms. Using Group Iterative Multiple Model Estimation (GIMME), an effective functional connectivity analysis, we explored an unsupervised model deriving subgroups based on path similarity in a priori defined regions of interest (ROIs) from brain regions implicated in the experience of pain and trauma. Three subgroups were identified by patterns in functional connection and differed significantly on several psychological measures despite similar demographic and diagnostic characteristics. The first subgroup was highly connected overall, was characterized by functional connectivity from the nucleus accumbens (NAc), the anterior cingulate cortex (ACC), and the posterior cingulate cortex (PCC) to the insula and scored low on pain and trauma symptoms. The second subgroup did not significantly differ from the first subgroup on pain and trauma measures but was characterized by functional connectivity from the ACC and NAc to the thalamus and from ACC to PCC. The third subgroup was characterized by functional connectivity from the thalamus and PCC to NAc and scored high on pain and trauma symptoms. Our results suggest that, despite demographic and diagnostic similarities, there may be neurobiologically dissociable biotypes with different mechanisms for managing pain and trauma. These findings may have implications for the determination of appropriate biotype-specific interventions that target these neurological systems.

Psycho-Neuro-Endocrine-Immunological Basis of the Placebo Effect: Potential Applications beyond Pain Therapy

The placebo effect can be defined as the improvement of symptoms in a patient after the administration of an innocuous substance in a context that induces expectations regarding its effects. During recent years, it has been discovered that the placebo response not only has neurobiological functions on analgesia, but that it is also capable of generating effects on the immune and endocrine systems. The possible integration of changes in different systems of the organism could favor the well-being of the individuals and go hand in hand with conventional treatment for multiple diseases. In this sense, classic conditioning and setting expectations stand out as psychological mechanisms implicated in the placebo effect. Recent advances in neuroimaging studies suggest a relationship between the placebo response and the opioid, cannabinoid, and monoaminergic systems. Likewise, a possible immune response conditioned by the placebo effect has been reported. There is evidence of immune suppression conditioned through the insular cortex and the amygdala, with noradrenalin as the responsible neurotransmitter. Finally, a conditioned response in the secretion of different hormones has been determined in different studies; however, the molecular mechanisms involved are not entirely known. Beyond studies about its mechanism of action, the placebo effect has proved to be useful in the clinical setting with promising results in the management of neurological, psychiatric, and immunologic disorders. However, more research is needed to better characterize its potential use. This review integrates current knowledge about the psycho-neuro-endocrine-immune basis of the placebo effect and its possible clinical applications.

Clinical Effects of Repetitive Transcranial Magnetic Stimulation of the Motor Cortex Are Associated With Changes in Resting-State Functional Connectivity in Patients With Fibromyalgia Syndrome

In this double-blinded, sham-controlled, counterbalanced, and crossover study, we investigated the potential neuroplasticity underlying pain relief and daily function improvements following repetitive transcranial magnetic stimulation of the motor cortex (M1-rTMS) in fibromyalgia syndrome (FMS) patients. Specifically, we used magnetic resonance imaging (MRI) to examine changes in brain structural and resting-state functional connectivity (rsFC) that correlated with improvements in FMS symptomology following M1-rTMS. Twenty-seven women with FMS underwent real and sham treatment series, each consisting of 10 daily treatments of 10Hz M1-rTMS over 2 weeks, with a washout period in between. Before and after each series, participants underwent anatomical and resting-state functional MRI scans and questionnaire assessments of FMS-related clinical pain and functional and psychological burdens. The expected reductions in FMS-related symptomology following M1-rTMS occurred with the real treatment only and correlated with rsFC changes in brain areas associated with pain processing and modulation. Specifically, between the ventromedial prefrontal cortex and the M1 (t = -5.54, corrected P = .002), the amygdala and the posterior insula (t = 5.81, corrected P = .044), and the anterior and posterior insula (t = 6.01, corrected P = .029). Neither treatment significantly changed brain structure. Therefore, we provide the first evidence of an association between the acute clinical effects of M1-rTMS in FMS and functional alterations of brain areas that have a significant role in the experience of chronic pain. Structural changes could potentially occur over a more extended treatment period. PERSPECTIVE: We show that the neurophysiological mechanism of the improvement in fibromyalgia symptoms following active, but not sham, rTMS applied to M1 involves changes in resting-state functional connectivity in sensory, affective and cognitive pain processing brain areas, thus substantiating the essence of fibromyalgia syndrome as a treatable brain-based disorder.

Placebo response vary between different types of sham acupuncture: A randomized double-blind trial in neck pain patients

Background

In prospective experimental studies of neck pain patients, it is difficult to determine whether responses to sham acupuncture differ from responses to real acupuncture due to the heterogeneous methodologies in control/sham interventions. Here we aim to compare the specific and nonspecific effects of electroacupuncture with four types of sham acupuncture.

Methods

In this double‐blind, sham‐controlled study, we randomly assigned 175 patients with neck pain to receive 10 sessions of electroacupuncture, shallow puncture, nonacupoint deep puncture, nonacupoint shallow puncture, or nonpenetration acupuncture. We used the Northwick Park Neck Pain Questionnaire (NPQ) as our primary outcome, and Short‐form McGill Pain Questionnaire, visual analog scale (VAS), and Pain Threshold as secondary outcomes to measure the changes from baseline to a 3‐month follow up.

Results

All groups, except nonacupoint shallow puncture, had significant improvement in all outcome measurements. Electroacupuncture only showed superior improvements than the shallow puncture, nonacupoint shallow puncture, and nonpenetration groups when compared using the NPQ and VAS scale (*p < 0.001). Interestingly, the nonacupoint shallow puncture produced even less placebo response than nonpenetration acupuncture.

Conclusion

Our study demonstrates the high variability of placebo response among different types of sham controls depending on the depth of needle insertion and the puncture location. An important implication of our results is nonacupoint deep puncture produced similar analgesic effects as electroacupuncture. Our study may shed a new light on the predominant underlying mechanisms among different types of sham acupuncture controls, which can help with interpreting the effect of acupuncture in other studies.

Trial registration

Chinese clinical trial registry (ChiCTR‐IOR‐15006886).

Significance

This study compared the observed specific and nonspecific analgesia effect in four different types of sham acupuncture stimulation with neck pain patients, assessed by four outcomes. Although all of the sham controls produced significant reduction in neck pain, electroacupuncture had superior significant improvement. Importantly, placebo responses differed significantly between the sham controls and responses were inconsistent according to different outcome assessments. This study emphasizes the importance of taking into consideration which sham control and method of outcome measurement were used in a pain research study when evaluating its results.

Intra-articular placebo effect in the treatment of knee osteoarthritis: a survey of the current clinical evidence

Knee osteoarthritis (KOA) is a debilitating disease characterized by chronic pain, stiffness, and decreased mobility. Intra-articular injectable therapies show good clinical efficacy in improving symptoms; however, these therapies and their comparators (intra-articular saline) have been associated with a large underlying placebo effect. We aimed to describe the existing evidence on the challenges, hypotheses, and potential solutions to mitigate the intra-articular placebo effect in clinical trials in KOA. A targeted literature review was conducted by searching Embase, MEDLINE®, and CENTRAL using predefined study selection criteria. All eligible studies identified were extracted for relevant data, and results were narratively summarized. Forty-three studies were included following screening. Challenges associated with the intra-articular placebo effect included its ability to mask the comparative efficacy of active treatments in trials (n = 7 studies), long-lasting effects (up to 6 months; n = 3), and substantial variation of placebo effect sizes across populations (n = 3). Hypotheses for the mechanism of the placebo effect included aspiration of synovial fluid during administration (n = 6) and dilution of inflammatory mediators (n = 2). Factors affecting the placebo effect size were more invasive routes of administration (e.g., injection versus oral; n = 4) and patient expectations (n = 2). Proposed solutions included the suggestion for readers to weigh the relevance of clinical trial evidence against the presence of large underlying placebo effects (n = 9), discontinuation of intra-articular saline as an appropriate placebo (n = 5), and inclusion of 'no treatment' or sham injection as a control (n = 4). The intra-articular placebo effect is a well-documented occurrence in KOA clinical trials, and it is suggested that it be accounted for when designing randomized controlled trials. Awareness and understanding of the intra-articular placebo effect in KOA are required for fair interpretation of clinical trial evidence.

Pain, negative affective states and opioid-based analgesics: Safer pain therapies to dampen addiction

Across centuries and civilizations opioids have been used to relieve pain. In our modern societies, opioid-based analgesics remain one of the most efficient treatments for acute pain. However, the long-term use of opioids can lead to the development of analgesic tolerance, opioid-induced hyperalgesia, opioid use disorders, and overdose, which can ultimately produce respiratory depressant effects with fatal consequences. In addition to the nociceptive sensory component of pain, negative affective states arising from persistent pain represent a risk factor for developing an opioid use disorder. Several studies have indicated that the increase in prescribed opioid analgesics since the 1990s represents the root of our current opioid epidemic. In this review, we will present our current knowledge on the endogenous opioid system within the pain neuroaxis and the plastic changes occurring in this system that may underlie the occurrence of pain-induced negative affect leading to misuse and abuse of opioid medications. Dissecting the allostatic neuronal changes occurring during pain is the most promising avenue to uncover novel targets for the development of safer pain medications. We will discuss this along with current and potential approaches to treat pain-induced negative affective states that lead to drug misuse. Moreover, this chapter will provide a discussion on potential avenues to reduce the abuse potential of new analgesic drugs and highlight a basis for future research and drug development based on recent advances in this field.

Effects of placebo administration on immune mechanisms and relationships with central endogenous opioid neurotransmission

Behavioral conditioning and expectation can have profound impact on animal and human physiology. Placebo, administered under positive expectation in clinical trials, can have potent effects on disease pathology, obscuring active medications. Emerging evidence suggests placebo-responsive neurotransmitter systems (e.g., endogenous opioid) regulate immune function by manipulating inflammatory proteins including IL-18, a potent pro-inflammatory, nociceptive cytokine implicated in pathophysiology of various diseases. Validation that neuroimmune interactions involving brain μ-opioid receptor (MOR) activity and plasma IL-18 underlie placebo analgesic expectation could have widespread clinical applications. Unfortunately, current lack of mechanistic clarity obfuscates clinical translation. To elucidate neuroimmune interactions underlying placebo analgesia, we exposed 37 healthy human volunteers to a standardized pain challenge on each of 2 days within a Positron Emission Tomography (PET) neuroimaging paradigm using the MOR selective radiotracer, ¹¹C-Carfentanil (CFN). Each day volunteers received an intervention (placebo under analgesic expectation or no treatment), completed PET scanning, and rated their pain experience. MOR BP_ND parametric maps were generated from PET scans using standard methods. Results showed placebo reduced plasma IL-18 during pain (W₇₄ = -3.7, p < 0.001), the extent correlating with reduction in pain scores. Placebo reduction in IL-18 covaried with placebo-induced endogenous opioid release in the left nucleus accumbens (T₁₄₈ = 3.33; p_uncorr < 0.001) and left amygdala (T₁₄₈ = 3.30; p_uncorr < 0.001). These findings are consistent with a modulating effect of placebo (under analgesic expectation in humans) on a potent nociceptive, pro-inflammatory cytokine (IL-18) and underlying relationships with endogenous opioid activity, a neurotransmitter system critically involved in pain, stress, and mood regulation.

The role of endogenous opioid neuropeptides in neurostimulation-driven analgesia

Due to the prevalence of chronic pain worldwide, there is an urgent need to improve pain management strategies. While opioid drugs have long been used to treat chronic pain, their use is severely limited by adverse effects and abuse liability. Neurostimulation techniques have emerged as a promising option for chronic pain that is refractory to other treatments. While different neurostimulation strategies have been applied to many neural structures implicated in pain processing, there is variability in efficacy between patients, underscoring the need to optimize neurostimulation techniques for use in pain management. This optimization requires a deeper understanding of the mechanisms underlying neurostimulation-induced pain relief. Here, we discuss the most commonly used neurostimulation techniques for treating chronic pain. We present evidence that neurostimulation-induced analgesia is in part driven by the release of endogenous opioids and that this endogenous opioid release is a common endpoint between different methods of neurostimulation. Finally, we introduce technological and clinical innovations that are being explored to optimize neurostimulation techniques for the treatment of pain, including multidisciplinary efforts between neuroscience research and clinical treatment that may refine the efficacy of neurostimulation based on its underlying mechanisms.

Engaging endogenous opioid circuits in pain affective processes

The pervasive use of opioid compounds for pain relief is rooted in their utility as one of the most effective therapeutic strategies for providing analgesia. While the detrimental side effects of these compounds have significantly contributed to the current opioid epidemic, opioids still provide millions of patients with reprieve from the relentless and agonizing experience of pain. The human experience of pain has long recognized the perceived unpleasantness entangled with a unique sensation that is immediate and identifiable from the first-person subjective vantage point as "painful." From this phenomenological perspective, how is it that opioids interfere with pain perception? Evidence from human lesion, neuroimaging, and preclinical functional neuroanatomy approaches is sculpting the view that opioids predominately alleviate the affective or inferential appraisal of nociceptive neural information. Thus, opioids weaken pain-associated unpleasantness rather than modulate perceived sensory qualities. Here, we discuss the historical theories of pain to demonstrate how modern neuroscience is revisiting these ideas to deconstruct the brain mechanisms driving the emergence of aversive pain perceptions. We further detail how targeting opioidergic signaling within affective or emotional brain circuits remains a strong avenue for developing targeted pharmacological and gene-therapy analgesic treatments that might reduce the dependence on current clinical opioid options.

What is the role of placebo in neurotherapeutics?

INTRODUCTION

The widespread use of the word 'placebo' in the medical literature emphasizes the importance of this phenomenon in modern biomedical sciences. Neuroscientific research over the past thirty years shows that placebo effects are genuine psychobiological events attributable to the overall therapeutic context, and can be robust in both laboratory and clinical settings.

AREAS COVERED

Here the authors describe the biological mechanisms and the clinical implications of placebo effects with particular emphasis on neurology and psychiatry, for example in pain, movement disorders, depression. In these conditions, a number of endogenous systems have been identified, such as endogenous opioids, endocannabinoids, and dopamine, which contribute to the placebo-induced benefit.

EXPERT OPINION

Every effort should be made to maximize the placebo effect and reduce its evil twin, the nocebo effect, in medical practice. This does not require the administration of a placebo, but rather the enhancement of the effects of pharmacological and nonpharmacological treatments through a good doctor-patient interaction.

Brainstem Mechanisms of Pain Modulation: A within-Subjects 7T fMRI Study of Placebo Analgesic and Nocebo Hyperalgesic Responses

Pain perception can be powerfully influenced by an individual's expectations and beliefs. Although the cortical circuitry responsible for pain modulation has been thoroughly investigated, the brainstem pathways involved in the modulatory phenomena of placebo analgesia and nocebo hyperalgesia remain to be directly addressed. This study used ultra-high-field 7 tesla functional MRI (fMRI) to accurately resolve differences in brainstem circuitry present during the generation of placebo analgesia and nocebo hyperalgesia in healthy human participants (N = 25, 12 male). Over 2 successive days, through blinded application of altered thermal stimuli, participants were deceptively conditioned to believe that two inert creams labeled lidocaine (placebo) and capsaicin (nocebo) were acting to modulate their pain relative to a third Vaseline (control) cream. In a subsequent test phase, fMRI image sets were collected while participants were given identical noxious stimuli to all three cream sites. Pain intensity ratings were collected and placebo and nocebo responses determined. Brainstem-specific fMRI analysis revealed altered activity in key pain modulatory nuclei, including a disparate recruitment of the periaqueductal gray (PAG)-rostral ventromedial medulla (RVM) pathway when both greater placebo and nocebo effects were observed. Additionally, we found that placebo and nocebo responses differentially activated the parabrachial nucleus but overlapped in engagement of the substantia nigra and locus coeruleus. These data reveal that placebo and nocebo effects are generated through differential engagement of the PAG-RVM pathway, which in concert with other brainstem sites likely influences the experience of pain by modulating activity at the level of the dorsal horn.SIGNIFICANCE STATEMENT Understanding endogenous pain modulatory mechanisms would support development of effective clinical treatment strategies for both acute and chronic pain. Specific brainstem nuclei have long been known to play a central role in nociceptive modulation; however, because of the small size and complex organization of the nuclei, previous neuroimaging efforts have been limited in directly identifying how these subcortical networks interact during the development of antinociceptive and pro-nociceptive effects. We used ultra-high-field fMRI to resolve brainstem structures and measure signal change during placebo analgesia and nocebo hyperalgesia. We define overlapping and disparate brainstem circuitry responsible for altering pain perception. These findings extend our understanding of the detailed organization and function of discrete brainstem nuclei involved in pain processing and modulation.

The Cholecystokinin Type 2 Receptor, a Pharmacological Target for Pain Management

Over the past decades, accumulating evidence has demonstrated a pivotal role of cholecystokinin type 2 receptor (CCK2R) in pain modulation. The established role of CCK2R activation in directly facilitating nociception has led to the development of several CCK2R antagonists, which have been shown to successfully alleviate pain in several rodent models of pain. However, the outcomes of clinical trials are more modest since they have not demonstrated the expected biological effect obtained in animals. Such discordances of results between preclinical and clinical studies suggest reconsidering our knowledge about the molecular basis of the pharmacology and functioning of CCK2R. This review focuses on the cellular localization of CCK2R specifically in the sensory nervous system and discusses in further detail the molecular mechanisms and signal transduction pathways involved in controlling pain perception. We then provide a comprehensive overview of the most successful compounds targeting CCK2R and report recent advances in pharmacological strategies used to achieve CCK2R modulation. We purposely distinguish between CCK2R benefits obtained in preclinical models and outcomes in clinical trials with different pain etiologies. Lastly, we emphasize the biological and clinical relevance of CCK2R as a promising target for the development of new treatments for pain management.

A social affective neuroscience lens on placebo analgesia

Pain is a fundamental experience that promotes survival. In humans, pain stands at the intersection of multiple health crises: chronic pain, the opioid epidemic, and health disparities. The study of placebo analgesia highlights how social, cognitive, and affective processes can directly shape pain, and identifies potential paths for mitigating these crises. This review examines recent progress in the study of placebo analgesia through affective science. It focuses on how placebo effects are shaped by expectations, affect, and the social context surrounding treatment, and discusses neurobiological mechanisms of placebo, highlighting unanswered questions and implications for health. Collaborations between clinicians and social and affective scientists can address outstanding questions and leverage placebo to reduce pain and improve human health.

Exploring scraping therapy: Contemporary views on an ancient healing - A review

Gua sha is a traditional healing technique that aims to create petechiae on the skin for a believed therapeutic benefit. Natural healings are mostly based on repeated observations and anecdotal information. Hypothetical model for healing does not always fit the modern understanding. Yet, the mechanisms underlying Gua Sha have not been empirically established. Contemporary scientific research can now explain some events of traditional therapies that were once a mystery. It is assumed that Gua Sha therapy can serve as a mechanical signal to enhance the immune surveillance function of the skin during the natural resolving of the petechiae, through which scraping may result in therapeutic benefits. The current review, without judging the past hypothetical model, attempts to interpret the experience of the ancient healings in terms of contemporary views and concepts.

μ Opioid Antagonist Naltrexone Partially Abolishes the Antidepressant Placebo Effect and Reduces Orbitofrontal Cortex Encoding of Reinforcement

BACKGROUND

Like placebo analgesia, the antidepressant placebo effect appears to involve cortical and subcortical endogenous opioid signaling, yet the mechanism through which opioid release affects mood remains unclear. The orbitofrontal cortex (OFC)-which integrates various attributes of a stimulus to predict associated outcomes-has been implicated in placebo effects and is rich in μ opioid receptors. We hypothesized that naltrexone blockade of μ opioid receptors would blunt OFC-dependent antidepressant placebo effects.

METHODS

Twenty psychotropic-free patients with major depressive disorder completed a randomized, double-blind, placebo-controlled crossover study of 1 oral dose of 50 mg of naltrexone or matching placebo immediately before completing 2 sessions of the antidepressant placebo functional magnetic resonance imaging task. This task manipulates placebo-associated expectancies and their reinforcement while assessing expected and actual mood improvement.

RESULTS

Behaviorally, manipulations of antidepressant placebo expectancies and their reinforcement had positive, interactive effects on participants' expectancy and mood ratings. The high-expectancy condition recruited the dorsolateral and ventrolateral prefrontal cortex, as well as dorsal attention stream regions. Interestingly, increased dorsolateral and ventrolateral prefrontal cortex brain responses appeared to attenuate the antidepressant placebo effect. The administration of 1 oral dose of naltrexone, compared with placebo, partially abolished the interaction of the expectancy and reinforcement manipulation on mood and blocked reinforcement-induced responses in the right central OFC.

CONCLUSIONS

Our results show preliminary evidence for the role of μ opioid central OFC modulation in antidepressant placebo effects by positively biasing the value of placebo based on reinforcement and enhancing subsequent hedonic experiences.

Thirty Years of Neuroscientific Investigation of Placebo and Nocebo: The Interesting, the Good, and the Bad

Over the past 30 years there has been a surge of research on the placebo effect using a neuroscientific approach. The interesting aspects of this effort are related to the identification of several biological mechanisms of both the placebo and nocebo effects, the latter of which is defined as a negative placebo effect. Some important translational implications have emerged both in the setting of clinical trials and in routine medical practice. One of the principal contributions of neuroscience has been to draw the attention of the scientific and medical communities to the important role of psychobiological factors in therapeutic outcomes, be they drug related or not. Indeed, many biological mechanisms triggered by placebos and nocebos resemble those modulated by drugs, suggesting a possible interaction between psychological factors and drug action. Unfortunately, this new knowledge regarding placebos has the potential of being dangerously exploited by pseudoscience. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Tapentadol and oxycodone reduce cingulate glutamate in healthy volunteers

Tapentadol and oxycodone are commonly used analgesics. Preclinical studies have shown that oxycodone modulates brain metabolites related to opioid pathways, whereas tapentadol also affects noradrenergic activity. However, knowledge about the function of the medications in the human brain is limited. The aim was to investigate effects of tapentadol and oxycodone on brain glutamate, the most important neurotransmitter in pain processing. Magnetic resonance spectroscopy was obtained in 21 healthy subjects from the anterior cingulate cortex, prefrontal cortex, and insula at baseline and after 14 days of treatment with either 50 mg tapentadol, 10 mg oxycodone (equipotent dose, both extended release) or placebo twice daily in a randomized double-blind cross-over study. Compared to baseline, decreased glutamate/creatine levels were identified in anterior cingulate cortex after tapentadol (1.26 ± 0.14 vs. 1.35 ± 0.18, P = .04) and oxycodone (1.26 ± 0.10 vs. 1.35 ± 0.12, P = .05) treatments, both with 7% reduction. This indicates that both analgesics modulate the glutamatergic system at the supraspinal level in humans.

Patient expectations about a clinical diagnostic test may influence the clinician's test interpretation

BACKGROUND

With medical information widely available, patients often have preconceived ideas regarding diagnostic procedures and management strategies.

OBJECTIVES

To investigate whether expectations, such as beliefs about the source of symptoms and knowledge about diagnostic tests, influence pain perception during a clinical diagnostic test.

DESIGN

Cross-sectional study.

METHODS

Pain was induced by intramuscular hypertonic saline infusion in the thenar muscles. In line with sample size calculations, fifteen participants were included. All participants received identical background information regarding basic median nerve biomechanics and basic concepts of differential diagnosis via mechanical loading of painful structures. Based on different explanations about the origin of their induced pain, half of the participants believed (correctly) they had 'muscle pain' and half believed (incorrectly) they had 'nerve pain'. Pain intensity and size of the painful area were evaluated in five different positions of the median nerve neurodynamic test (ULNT1 _MEDIAN). Data were analysed with two-way analyses of variance.

RESULTS

/findings: Changes in pain in the ULNT1 _MEDIAN positions were different between the 'muscle pain' and 'nerve pain' group (p < 0.001). In line with their expectations, the 'muscle pain' group demonstrated no changes in pain throughout the test (p > 0.38). In contrast, pain intensity (p ≤ 0.003) and size of the painful area (p ≤ 0.03) increased and decreased in the 'nerve pain' group consistent with their expectations and the level of mechanical nerve loading.

CONCLUSION

Pain perception during a clinical diagnostic test may be substantially influenced by pain anticipation. Moreover, pain was more aligned with beliefs and expectations than with the actual pathobiological process.

Arbiters of endogenous opioid analgesia: role of CNS estrogenic and glutamatergic systems

Nociception and opioid antinociception in females are pliable processes, varying qualitatively and quantitatively over the reproductive cycle. Spinal estrogenic signaling via membrane estrogen receptors (mERs), in combination with multiple other signaling molecules [spinal dynorphin, kappa-opioid receptors (KOR), glutamate and metabotropic glutamate receptor 1 (mGluR₁)], appears to function as a master coordinator, parsing functionality between pronociception and antinociception. This provides a window into pharmacologically accessing intrinsic opioid analgesic/anti-allodynic systems. In diestrus, membrane estrogen receptor alpha (mERα) signals via mGluR₁ to suppress spinal endomorphin 2 (EM2) analgesia. Strikingly, in the absence of exogenous opioids, interfering with this suppression in a chronic pain model elicits opioid anti-allodynia, revealing contributions of endogenous opioid(s). In proestrus, robust spinal EM2 analgesia is manifest but this requires spinal dynorphin/KOR and glutamate-activated mGluR₁. Furthermore, spinal mGluR₁ blockade in a proestrus chronic pain animal (eliminating spinal EM2 analgesia) exacerbates mechanical allodynia, revealing tempering by endogenous opioid(s). A complex containing mu-opioid receptor, KOR, aromatase, mGluRs, and mERα are foundational to eliciting endogenous opioid anti-allodynia. Aromatase-mERα oligomers are also plentiful, in a central nervous system region-specific fashion. These can be independently regulated and allow estrogens to act intracellularly within the same signaling complex in which they are synthesized, explaining asynchronous relationships between circulating estrogens and central nervous system estrogen functionalities. Observations with EM2 highlight the translational relevance of extensively characterizing exogenous responsiveness to endogenous opioids and the neuronal circuits that mediate them along with the multiplicity of estrogenic systems that concomitantly function in phase and out-of-phase with the reproductive cycle.

Opioid Specific Effects on Central Processing of Sensation and Pain: A Randomized, Cross-Over, Placebo-Controlled Study

Moderate to severe pain is often treated with opioids, but central mechanisms underlying opioid analgesia are poorly understood. Findings thus far have been contradictory and none could infer opioid specific effects. This placebo-controlled, randomized, 2-way cross-over, double-blinded study aimed to explore opioid specific effects on central processing of external stimuli. Twenty healthy male volunteers were included and 3 sets of assessments were done at each of the 2 visits: 1) baseline, 2) during continuous morphine or placebo intravenous infusion and 3) during simultaneous morphine + naloxone or placebo infusion. Opioid antagonist naloxone was introduced in order to investigate opioid specific effects by observing which morphine effects are reversed by this intervention. Quantitative sensory testing, spinal nociceptive withdrawal reflexes (NWR), spinal electroencephalography (EEG), cortical EEG responses to external stimuli and resting EEG were measured and analyzed. Longer lasting pain (cold-pressor test - hand in 2° water for 2 minutes, tetanic electrical), deeper structure pain (bone pressure) and strong nociceptive (NWR) stimulations were the most sensitive quantitative sensory testing measures of opioid analgesia. In line with this, the principal opioid specific central changes were seen in NWRs, EEG responses to NWRs and cold-pressor EEG. The magnitude of NWRs together with amplitudes and insular source strengths of the corresponding EEG responses were attenuated. The decreases in EEG activity were correlated to subjective unpleasantness scores. Brain activity underlying slow cold-pressor EEG (1-4Hz) was decreased, whereas the brain activity underlying faster EEG (8-12Hz) was increased. These changes were strongly correlated to subjective pain relief. This study points to evidence of opioid specific effects on perception of external stimuli and the underlying central responses. The analgesic response to opioids is likely a synergy of opioids acting at both spinal and supra-spinal levels of the central nervous system. Due to the strong correlations with pain relief, the changes in EEG signals during cold-pressor test have the potential to serve as biomarkers of opioid analgesia. PERSPECTIVE: This exploratory study presents evidence of opioid specific effects on the pain system at peripheral and central levels. The findings give insights into which measures are the most sensitive for assessing opioid-specific effects.

The Role of Expectations and Endogenous Opioids in Mindfulness-Based Relief of Experimentally Induced Acute Pain

OBJECTIVE

Expectations contribute to cognitive pain modulation through opioidergically mediated descending inhibition. Mindfulness meditation reduces pain independent of endogenous opioids, engaging unique corticothalamocortical mechanisms. However, it remains unknown whether expectations for pain relief predict mindfulness-induced analgesia and if these expectations are modified by endogenous opioids.

METHODS

In this secondary analysis of previously published work, 78 pain-free participants (mean age, 27 ± 7 years; 50% women) were randomized to a four-session mindfulness meditation or book listening regimen. Expectations for intervention-induced pain relief were assessed before and after each intervention. Pain ratings were examined after meditation or rest (control group) during noxious heat (49°C) and intravenous administration of saline placebo or the opioid antagonist naloxone (0.15 mg/kg bolus + 0.1 mg kg-1 h-1 infusion.

RESULTS

Mindfulness significantly lowered pain during saline and naloxone infusion. Higher expected pain relief from mindfulness predicted lower pain intensity (r(40) = -0.41, p = .009). The relationship between meditation-related expectations and pain intensity reductions was exhibited during naloxone (r(20) = -0.76, p < .001) but not saline (r(20) = -0.22, p = .36). Expectations for book listening-based analgesia did not significantly predict pain changes during saline (r(20) = -0.37, p = .11) or naloxone (r(18) = 0.26, p = .30) in the control group.

CONCLUSIONS

These novel findings demonstrate a significant role for expectations in mindfulness-based pain relief. However, this role was minimal during saline and stronger during opioid blockade, despite similar pain reductions. This supports growing evidence that mindfulness engages multiple mechanisms to reduce pain, suggesting that mindfulness might be an effective pain-reducing technique even for individuals with low expectations for pain relief.

Naltrexone during pain conditioning: A double-blind placebo-controlled experimental trial

Naltrexone reversibly blocks the effects of opioids and has been shown to decrease placebo analgesia. However, it is not clear (1) to what extent naltrexone affects pain modulation in a nontreatment context, for example, in response to pain cues or (2) how naltrexone given prior to pain-cue learning shapes pain responses. In a double-blind procedure prior to pain-cue conditioning, 30 healthy participants were randomized to receive an oral dose of naltrexone (50 mg) or inert pill. During functional magnetic resonance imaging, high and low pain pressures were paired with two different visual cues: a high pain cue and a low pain cue (learning sequence). During a test sequence, medium levels of pressure were used for both cues and the difference in subjective pain ratings following high and low pain cues was calculated. Results showed significant conditioned pain responses across groups (P < .001); however, no significant difference between participants receiving naltrexone or inert pill (P = .193). There was a significant correlation between the difference in high and low pain ratings during the learning sequence and the effect of high and low pain cues during the test sequence (r = .575, P = .002). Functional magnetic resonance imaging analyses revealed no significant difference in brain activation between groups. Here, we demonstrate comparable learning of pain responses in participants treated with naltrexone or inert pill. The results point to the possibility that associative learning, and conditional responding to pain cues, is not dependent on endogenous opioids. Our results, using pain-cue conditioning to create reduced pain responses, contrast previous studies where opioid antagonists significantly reduced the placebo effect in treatment of pain.

Manipulating placebo analgesia and nocebo hyperalgesia by changing brain excitability

Harnessing placebo and nocebo effects has significant implications for research and medical practice. Placebo analgesia and nocebo hyperalgesia, the most well-studied placebo and nocebo effects, are thought to initiate from the dorsal lateral prefrontal cortex (DLPFC) and then trigger the brain's descending pain modulatory system and other pain regulation pathways. Combining repeated transcranial direct current stimulation (tDCS), an expectancy manipulation model, and functional MRI, we investigated the modulatory effects of anodal and cathodal tDCS at the right DLPFC on placebo analgesia and nocebo hyperalgesia using a randomized, double-blind and sham-controlled design. We found that compared with sham tDCS, active tDCS could 1) boost placebo and blunt nocebo effects and 2) modulate brain activity and connectivity associated with placebo analgesia and nocebo hyperalgesia. These results provide a basis for mechanistic manipulation of placebo and nocebo effects and may lead to improved clinical outcomes in medical practice.

The Effect of Tai Chi Chuan on Emotional Health: Potential Mechanisms and Prefrontal Cortex Hypothesis

Deep involvement in the negative mood over long periods of time likely results in emotional disturbances/disorders and poor mental health. Tai Chi Chuan (TCC) is regarded as a typical mind-body practice combining aerobic exercise and meditation to prevent and treat negative mood. Although there are an increasing number of TCC studies examining anxiety, depression, and mental stress, the mechanisms underlying these negative emotions are not fully understood. This review study examined TCC studies related to emotional health from both clinical patients and healthy individuals. Next, several potential mechanisms from physiological, psychological, and neurological perspectives were evaluated based on direct and indirect research evidence. We reviewed recent functional magnetic resonance imaging studies, which demonstrated changes in brain anatomy and function, mainly in the prefrontal cortex, following TCC practice. Finally, the effects of TCC on emotion/mental health is depicted with a prefrontal cortex hypothesis that proposed “an immune system of the mind” indicating the role of the prefrontal cortex as a flexible hub in regulating an individual's mental health. The prefrontal cortex is likely a key biomarker among the multiple complex neural correlates to help an individual manage negative emotions/mental health. Future research is needed to examine TCC effects on mental health by examining the relationship between the executive control system (mainly prefrontal cortex) and limbic network (including amygdala, insula, and hippocampal gyrus).

Ethnic disparities in pain processing among healthy adults: μ-opioid receptor binding potential as a putative mechanism

Although ethnic differences in pain perception are well documented, the underlying mechanism for these outcomes has not been established. µ-opioid receptor (MOR) function might contribute to this disparity, given that MORs play a key role in pain sensitivity and modulation. However, no study has characterized ethnic differences in MOR physiology. This study sought to address this knowledge gap by examining differences in µ-selective agonist binding potential (BPND; [C]-Carfentanil) between 27 non-Hispanic black (NHB) and 27 demographically similar, non-Hispanic white participants. Participants completed questionnaires and two 90-minute high-resolution research tomograph positron emission tomography (PET) imaging sessions. During PET imaging, a capsaicin or control cream was applied to individuals' arms, and pain ratings were collected. Bonferroni-corrected PET volumes of interest analyses revealed significantly greater [C]-Carfentanil BPND among NHB participants in bilateral ventral striatum ([left]: F1,52 = 16.38, P < 0.001; [right]: F1,52 = 21.76, P < 0.001), bilateral dorsolateral prefrontal cortex ([left] F1,52 = 17.3, P < 0.001; [right]: F1,52 = 14.17, P < 0.001), bilateral subgenual anterior cingulate cortex ([left]: F1,52 = 10.4, P = 0.002; [right]: F1,52 = 12.91, P = 0.001), and right insula (F1,52 = 11.0, P = 0.002). However, there were no significant main effects of condition or ethnicity × condition interaction effects across models, likely attributable to individual variability in the direction of change within groups. BPND values were significantly correlated with pain ratings collected during the capsaicin condition (r range = 0.34-0.46, P range = 0.01-0.001). Results suggest that NHB individuals might have generally greater unoccupied MOR density than non-Hispanic white peers. Findings have implications for physiological differences underlying ethnicity-related pain disparities. If replicated, these results further emphasize the need for tailored treatments in historically underserved populations.