Distinct neural networks subserve placebo analgesia and nocebo hyperalgesia

Forebrain networks driving brainstem pain modulatory circuits during nocebo hyperalgesia in healthy humans

ABSTRACT

Prior experiences, conditioning cues, and expectations of improvement are essential for nocebo hyperalgesia expression. The neural circuits that communicate with brainstem pain modulatory nuclei during nocebo hyperalgesia responsivity are underexplored. In this study, we employed a classical conditioning and expectation model in 25 healthy human participants and measured brain activity using ultra-high field functional magnetic resonance imaging. We assessed forebrain activity changes as well as noxious stimulus-independent and -dependent connectivity changes with the lateral midbrain periaqueductal gray matter (lPAG). We found hyperalgesia-related signal increases in the orbitofrontal cortex, insula, and amygdala. In addition, we found stimulus-dependent lPAG connectivity changes with the orbitofrontal, anterior cingulate, and dorsolateral prefrontal cortices and stimulus-independent lPAG connectivity with the anterior cingulate cortex, dorsolateral prefrontal cortex, and nucleus accumbens during hyperalgesia. Whilst these connectivity changes are all associated with hyperalgesia, dynamic causal modelling analysis revealed that the dorsolateral prefrontal cortex was principally responsible for driving the lPAG. Overall, our results show that there is a complex relationship between forebrain activation and connectivity with brainstem pain modulation circuitry that results in the behavioural expression of nocebo hyperalgesia.

A scoping review of placebo and nocebo responses and effects: insights for clinical trials and practice

Placebo and nocebo responses and effects influence treatment outcomes across a variety of conditions. The current scoping review aims to synthesise evidence from systematic reviews and meta-analyses in both clinical and healthy populations, elucidating key determinants of placebo and nocebo responses and effects, including individual, clinical, psychological and contextual factors. Among the 306 publications identified, 83% were meta-analyses and 17% systematic reviews, with a predominance of research in medical specialties (81.7%) such as psychiatry and neurology. Placebo responses were significantly more studied than nocebo responses. Individual determinants (e.g., age), clinical determinants (e.g., baseline symptom severity) and psychological determinants (e.g., expectations) were found to influence placebo and nocebo outcomes. Contextual determinants, including trial design and the method of treatment administration, also played critical roles. Several key underinvestigated areas in the current body of systematic reviews and meta-analyses were also identified. This scoping review highlights valuable insights into the determinants of placebo and nocebo responses and effects on a group level, potentially offering practical implications for optimising clinical trial designs and enhancing patient care strategies in clinical practice. However, to fully leverage these benefits, it is crucial to address the underexplored topics through more rigorous investigations using a person-centred perspective.

The neural dynamics of positive and negative expectations of pain

Pain is heavily modulated by expectations. Whereas the integration of expectations with sensory information has been examined in some detail, little is known about how positive and negative expectations are generated and their neural dynamics from generation over anticipation to the integration with sensory information. The present preregistered study employed a novel paradigm to induce positive and negative expectations on a trial-by-trial basis and examined the neural mechanisms using combined EEG-fMRI measurements (n=50). We observed substantially different neural representations between the anticipatory and the actual pain period. In the anticipation phase i.e., before the nociceptive input, the insular cortex, dorsolateral prefrontal cortex (DLPFC), and anterior cingulate cortex (ACC) showed increased activity for directed expectations regardless of their valence. Interestingly, a differentiation between positive and negative expectations within the majority of areas only occurred after the arrival of nociceptive information. FMRI-informed EEG analyses could reliably track the temporal sequence of processing showing an early effect in the DLPFC, followed by the anterior insula and late effects in the ACC. The observed effects indicate the involvement of different expectation-related subprocesses, including the transformation of visual information into a value signal that is maintained and differentiated according to its valence only during stimulus processing.

Neural correlates of working memory training: An fMRI meta-analysis

Working memory (WM) can be improved by cognitive training. Numerous studies examined neural mechanisms underlying WM training, although with differing conclusions. Therefore, we conducted a meta-analysis to examine the neural substrates underlying WM training in healthy adults. Findings from global analyses showed substantial neural changes in the frontoparietal and subcortical regions. Results from training dosage analyses of WM training showed that shorter WM training could produce neural changes in the frontoparietal regions, whereas longer WM training could produce changes in the subcortical regions (striatum, anterior cingulate cortex, and insula). WM training-induced neural changes were also moderated by the type of training task, with updating tasks inducing neural changes in more regions than maintenance tasks. Overall, these results indicate that the neural changes associated with WM training occur in the frontoparietal network and dopamine-related brain areas, extending previous meta-analyses on WM training and advancing our understanding of the neural underpinnings of WM training effects.

Neural mechanisms underlying placebo and nocebo effects in tonic muscle pain

Pain is a highly subjective and multidimensional experience, significantly influenced by various psychological factors. Placebo analgesia and nocebo hyperalgesia exemplify this influence, where inert treatments result in pain relief or exacerbation, respectively. While extensive research has elucidated the psychological and neural mechanisms behind these effects, most studies have focused on transient pain stimuli. To explore these mechanisms in the context of tonic pain, we conducted a study using a 15-minute tonic muscle pain induction procedure, where hypertonic saline was infused into the left masseter of healthy participants. We collected real-time Visual Analogue Scale (VAS) scores and functional magnetic resonance imaging (fMRI) data during the induction of placebo analgesia and nocebo hyperalgesia via conditioned learning. Our findings revealed that placebo analgesia was more pronounced and lasted longer than nocebo hyperalgesia. Real-time pain ratings correlated significantly with neural activity in several brain regions. Notably, the putamen was implicated in both effects, while the caudate and other regions were differentially involved in placebo and nocebo effects. These findings confirm that the tonic muscle pain paradigm can be used to investigate the mechanisms of placebo and nocebo effects and indicate that placebo analgesia and nocebo hyperalgesia may have more distinct than common neural bases.

The expectations humans have of a pleasurable sensation asymmetrically shape neuronal responses and subjective experiences to hot sauce

Expectations shape our perception, profoundly influencing how we interpret the world. Positive expectations about sensory stimuli can alleviate distress and reduce pain (e.g., placebo effect), while negative expectations may heighten anxiety and exacerbate pain (e.g., nocebo effect). To investigate the impact of the (an)hedonic aspect of expectations on subjective experiences, we measured neurobehavioral responses to the taste of hot sauce among participants with heterogeneous taste preferences. By identifying participants who "liked" versus those who strongly "disliked" spicy flavors and by providing contextual cues about the spiciness of the sauce to be tasted, we dissociated the effects of positive and negative expectations from sensory stimuli (i.e., visual and gustatory stimuli), which were the same across all participants. Our results indicate that positive expectations lead to modulations in the intensity of subjective experience. These modulations were accompanied by increased activity in brain regions previously linked to information integration and the placebo effect, including the anterior insula, dorsolateral prefrontal cortex, and dorsal anterior cingulate cortex, as well as a predefined "pleasure signature." In contrast, negative expectations decreased hedonic experience and increased neural activity in the previously validated "Neurological Pain Signature" network. These findings demonstrate that hedonic aspects of one's expectations asymmetrically shape how the brain processes sensory input and associated behavioral reports of one's subjective experiences of intensity, pleasure, and pain. Our results suggest a dissociable impact of hedonic information: positive expectations facilitate higher-level information integration and reward processing, while negative expectations prime lower-level nociceptive and affective processes. This study demonstrates the powerful role of hedonic expectations in shaping subjective reality and suggests potential avenues for consumer and therapeutic interventions targeting expectation-driven neural processes.

CBMAT: a MATLAB toolbox for data preparation and post hoc analyses in neuroimaging meta-analyses

Coordinate-based meta-analysis (CBMA) is a powerful technique in the field of human brain imaging research. Due to its intense usage, several procedures for data preparation and post hoc analyses have been proposed so far. However, these steps are often performed manually by the researcher, and are therefore potentially prone to error and time-consuming. We hence developed the Coordinate-Based Meta-Analyses Toolbox (CBMAT) to provide a suite of user-friendly and automated MATLAB® functions allowing one to perform all these procedures in a fast, reproducible and reliable way. Besides the description of the code, in the present paper we also provide an annotated example of using CBMAT on a dataset including 34 experiments. CBMAT can therefore substantially improve the way data are handled when performing CBMAs. The code can be downloaded from https://github.com/Jordi-Manuello/CBMAT.git .

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

Learning pain from others: a systematic review and meta-analysis of studies on placebo hypoalgesia and nocebo hyperalgesia induced by observational learning

ABSTRACT

Observing someone experience pain relief or exacerbation after an intervention may induce placebo hypoalgesia or nocebo hyperalgesia. Understanding the factors that contribute to these effects could help in the development of strategies for optimizing treatment of chronic pain conditions. We systematically reviewed and meta-analyzed the literature on placebo hypoalgesia and nocebo hyperalgesia induced by observational learning (OL). A systematic literature search was conducted in the databases PubMed, PsycINFO, Web of Science, ScienceDirect, PsycARTICLES, Scopus, and Academic Search Ultimate. Twenty-one studies were included in the systematic review, 17 of which were suitable for meta-analysis (18 experiments; n = 764 healthy individuals). The primary end point was the standardized mean difference (SMD) for pain following placebo cues associated during OL with low vs high pain. Observational learning had a small-to-medium effect on pain ratings (SMD 0.44; 95% confidence interval [CI] 0.21-0.68; P < 0.01) and a large effect on pain expectancy (SMD 1.11; 95% CI 0.49-2.04; P < 0.01). The type of observation (in-person vs videotaped) modulated the magnitude of placebo hypoalgesia/nocebo hyperalgesia ( P < 0.01), whereas placebo type did not ( P = 0.23). Finally, OL was more effective when observers' empathic concern (but no other empathy-related factors) was higher ( r = 0.14; 95% CI 0.01-0.27; P = 0.03). Overall, the meta-analysis demonstrates that OL can shape placebo hypoalgesia and nocebo hyperalgesia. More research is needed to identify predictors of these effects and to study them in clinical populations. In the future, OL could be an important tool to help maximize placebo hypoalgesia in clinical settings.

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.

The Temporal Modulation of Nocebo Hyperalgesia in a Model of Sustained Pain

BACKGROUND

The direction and the magnitude of verbal suggestions have been shown to be strong modulators of nocebo hyperalgesia, while little attention has been given to the role of their temporal content. Here, we investigate whether temporal suggestions modulate the timing of nocebo hyperalgesia in an experimental model of sustained pain.

METHODS

Fifty-one healthy participants were allocated to one of three groups. Participants received an inert cream and were instructed that the agent had either hyperalgesic properties setting in after 5 (Nocebo 5, N5) or 30 (Nocebo 30, N30) minutes from cream application, or hydrating properties (No Expectation Group, NE). Pain was induced by the Cold Pressure Test (CPT) which was repeated before cream application (baseline) and after 10 (Test10) and 35 (Test35) minutes. Changes in pain tolerance and in HR at each test point in respect to baseline were compared between the three groups.

RESULTS

Tolerance change at Test 10 (Δ10) was greater in N5 (MED = -36.8; IQR = 20.9) compared to NE (MED = -5.3; IQR = 22.4; p < 0.001) and N30 (MED = 0.0; IQR = 23.1; p < 0.001), showing that hyperalgesia was only present in the group that expected the effect of the cream to set in early. Tolerance change at Test 35 (Δ35) was greater in N5 (MED = -36.3; IQR = 35.3; p = 0.002) and in N30 (MED = -33.3; IQR = 34.8; p = 0.009) compared to NE, indicating delayed onset of hyperalgesia in N30, and sustained hyperalgesia in N5. No group differences were found for HR.

CONCLUSIONS

Our study demonstrated that temporal expectations shift nocebo response onset in a model of sustained pain.

Associations Between Interindividual Differences, Expectations and Placebo and Nocebo Effects in Itch

Introduction: Placebo and nocebo effects are positive and negative health outcomes that can be elicited by the psychosocial context. They can be mediated by expectations, and may emerge in somatic symptoms even when people are aware of these effects. Interindividual differences (e.g., in personality, affective states) could impact placebo and nocebo responding, but findings are inconsistent. Methods: The current work examined expectation as a mediator of the association between verbal placebo and nocebo suggestions (VSs) and histamine-induced itch across three experimental studies. Moreover, we examined whether interindividual differences (e.g., in optimism, neuroticism, behavioral activation system (BAS), body ignorance) modulated: (1) the direct association between VSs and itch (direct moderation), and (2) the indirect, expectation-mediated association between VSs and itch (moderated mediation). Positive VSs were compared to neutral instructions (Study 1; n = 92) or negative VSs (Studies 2+3; n = 203) in an open-label (i.e., explaining placebo and nocebo effects) or closed-label (concealed) context using PROCESS. First, mediation of VSs effects on itch by expectations was tested. Next, moderation by individual traits was explored using conditional process analyses. Results: The effects of VSs on itch were significantly mediated by expectation in Study 1 and in the open-label (but not closed-label) contexts of Studies 2 and 3. Ignorance of bodily signals marginally moderated the direct effects of VSs on itch when closed-label suggestions were given: at low levels of body ignorance, effects of positive and negative VSs were stronger. Moreover, moderated mediation was observed in the open-label groups of Studies 2 and 3: The expectation-mediated effects of VSs on itch were stronger when BAS drive was lower. Conclusion: Overall, the effects of VSs on itch were mediated by expectations in the open-label, but not the closed-label context. Moreover, the current work suggests that placebo and nocebo effects may be moderated by ignorance of bodily signals and the BAS. There was limited evidence that other interindividual differences modulated placebo and nocebo responding in itch.

Better living through understanding the insula: Why subregions can make all the difference

Insula function is considered critical for many motivated behaviors, with proposed functions ranging from attention, behavioral control, emotional regulation, goal-directed and aversion-resistant responding. Further, the insula is implicated in many neuropsychiatric conditions including substance abuse. More recently, multiple insula subregions have been distinguished based on anatomy, connectivity, and functional contributions. Generally, posterior insula is thought to encode more somatosensory inputs, which integrate with limbic/emotional information in middle insula, that in turn integrate with cognitive processes in anterior insula. Together, these regions provide rapid interoceptive information about the current or predicted situation, facilitating autonomic recruitment and quick, flexible action. Here, we seek to create a robust foundation from which to understand potential subregion differences, and provide direction for future studies. We address subregion differences across humans and rodents, so that the latter's mechanistic interventions can best mesh with clinical relevance of human conditions. We first consider the insula's suggested roles in humans, then compare subregional studies, and finally describe rodent work. One primary goal is to encourage precision in describing insula subregions, since imprecision (e.g. including both posterior and anterior studies when describing insula work) does a disservice to a larger understanding of insula contributions. Additionally, we note that specific task details can greatly impact recruitment of various subregions, requiring care and nuance in design and interpretation of studies. Nonetheless, the central ethological importance of the insula makes continued research to uncover mechanistic, mood, and behavioral contributions of paramount importance and interest. This article is part of the special Issue on 'Neurocircuitry Modulating Drug and Alcohol Abuse'.