Brain Network to Placebo and Nocebo Responses in Acute Experimental Lower Back Pain: A Multivariate Granger Causality Analysis of fMRI Data

"The Dark Side of Musculoskeletal Care": Why Do Ineffective Techniques Seem to Work? A Comprehensive Review of Complementary and Alternative Therapies

The increasing interest in complementary and alternative medicines (CAMs) for musculoskeletal care has sparked significant debate, particularly regarding their biological plausibility and clinical effectiveness. This comprehensive review critically examines the use of two of the most widely utilized CAMs-osteopathy and chiropractic care-over the past 25 years, focusing on their biological plausibility, clinical effectiveness, and potential mechanisms of action. Our analysis of current research and clinical studies reveals that osteopathy and chiropractic are based on concepts such as "somatic dysfunction" and "vertebral subluxation", which lack robust empirical validation. While these therapies are often presented as credible treatment options, studies evaluating their effectiveness frequently exhibit serious methodological flaws, providing insufficient empirical support for their recommendation as first-line treatments for musculoskeletal conditions. The effects and mechanisms underlying osteopathy and chiropractic remain poorly understood. However, placebo responses-mediated by the interaction of contextual, psychological, and non-specific factors-appear to play a significant role in observed outcomes. The integration of therapies with limited biological plausibility, whose effects may primarily rely on placebo effects, into healthcare systems raises important ethical dilemmas. This review highlights the need for rigorous adherence to scientific principles and calls for a more comprehensive investigation into biobehavioral, contextual, and psychosocial factors that interact with the specific effects of these interventions. Such efforts are essential to advancing our understanding of CAMs, enhancing clinical decision-making, promoting ethical practices, and guiding future research aimed at improving patient care in musculoskeletal disorders.

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.

NHSMM-MAR-sdNC: A novel data-driven computational framework for state-dependent effective connectivity analysis

The brain exhibits intrinsic dynamics characterized by spontaneous spatiotemporal reorganization of neural activity or metastability, which is associated closely with functional integration and segregation. Compared to dynamic functional connectivity, state-dependent effective connectivity (i.e., dynamic effective connectivity) is more suitable for exploring the metastability as its ability to infer causalities between brain regions. However, methods for state-dependent effective connectivity are scarce and urgently needed. In this study, a novel data-driven computational framework, named NHSMM-MAR-sdNC integrating nonparametric hidden semi-Markov model combined with multivariate autoregressive model and state-dependent new causality, is proposed to investigate the state-dependent effective connectivity. The framework is not constrained by any biological assumptions. Furthermore, state number can be inferred from the observed data directly and the state duration distributions will be estimated explicitly rather than restricted by geometric form, which overcomes limitations of hidden Markov model. Experimental results of synthetic data show that the framework can identify the state number adaptively and the state-dependent causality networks accurately. The dynamics of state-related causality networks are also revealed by the new method on real-world resting-state fMRI data. Our method provides a new data-driven computational framework for identifying state-dependent effective connectivity, which will facilitate the identification and assessment of metastability and itinerant dynamics of the brain.

A new experimental rat model of nocebo-related nausea involving double mechanisms of observational learning and conditioning

AIM

The nocebo effect, such as nausea and vomiting, is one of the major reasons patients discontinue therapy. The underlying mechanisms remain unknown due to a lack of reliable experimental models. The goal of this study was to develop a new animal model of nocebo-related nausea by combining observational learning and Pavlovian conditioning paradigms.

METHODS

Male Sprague-Dawley rats with nitroglycerin-induced migraine were given 0.9% saline (a placebo) or LiCl (a nausea inducer) following headache relief, according to different paradigms.

RESULTS

Both strategies provoked nocebo nausea responses, with the conditioning paradigm having a greater induction impact. The superposition of two mechanisms led to a further increase in nausea responses. A preliminary investigation of the underlying mechanism revealed clearly raised peripheral and central cholecystokinin (CCK) levels, as well as specific changes in the 5-hydroxytryptamine and cannabinoid systems. Brain networks related to emotion, cognition, and visceral sense expressed higher c-Fos-positive neurons, including the anterior cingulate cortex (ACC), insula, basolateral amygdala (BLA), thalamic paraventricular nucleus (PVT), hypothalamic paraventricular nucleus (PVN), nucleus tractus solitarius (NTS), periaqueductal gray (PAG), and dorsal raphe nucleus-dorsal part (DRD). We also found that nausea expectances in the model could last for at least 12 days.

CONCLUSION

The present study provides a useful experimental model of nocebo nausea that might be used to develop potential molecular pathways and therapeutic strategies for nocebo.

Multimodal non-invasive non-pharmacological therapies for chronic pain: mechanisms and progress

BACKGROUND

Chronic pain conditions impose significant burdens worldwide. Pharmacological treatments like opioids have limitations. Non-invasive non-pharmacological therapies (NINPT) encompass diverse interventions including physical, psychological, complementary and alternative approaches, and other innovative techniques that provide analgesic options for chronic pain without medications.

MAIN BODY

This review elucidates the mechanisms of major NINPT modalities and synthesizes evidence for their clinical potential across chronic pain populations. NINPT leverages peripheral, spinal, and supraspinal mechanisms to restore normal pain processing and limit central sensitization. However, heterogeneity in treatment protocols and individual responses warrants optimization through precision medicine approaches.

CONCLUSION

Future adoption of NINPT requires addressing limitations in standardization and accessibility as well as synergistic combination with emerging therapies. Overall, this review highlights the promise of NINPT as a valuable complementary option ready for integration into contemporary pain medicine paradigms to improve patient care and outcomes.

Amplified gut feelings under inflammation and depressed mood: A randomized fMRI trial on interoceptive pain in healthy volunteers

BACKGROUND

Inflammation and depressed mood constitute clinically relevant vulnerability factors for enhanced interoceptive sensitivity and chronic visceral pain, but their putative interaction remains untested in human mechanistic studies. We tested interaction effects of acute systemic inflammation and sad mood on the expectation and experience of visceral pain by combining experimental endotoxemia with a mood induction paradigm.

METHODS

The double-blind, placebo-controlled, balanced crossover fMRI-trial in N=39 healthy male and female volunteers involved 2 study days with either intravenous administration of low-dose lipopolysaccharide (LPS, 0.4ng/kg body weight; inflammation condition) or saline (placebo condition). On each study, day two scanning sessions were conducted in an experimentally induced negative (i.e., sad) and in a neutral mood state, accomplished in balanced order. As a model of visceral pain, rectal distensions were implemented, which were initially calibrated to be moderately painful. In all sessions, an identical series of visceral pain stimuli was accomplished, signaled by predictive visual conditioning cues to assess pain anticipation. We assessed neural activation during the expectation and experience of visceral pain, along with unpleasantness ratings in a condition combining an inflammatory state with sad mood and in control conditions. All statistical analyses were accomplished using sex as covariate.

RESULTS

LPS administration led to an acute systemic inflammatory response (inflammation X time interaction effects for TNF-α, IL-6, and sickness symptoms, all p<.001). The mood paradigm effectively induced distinct mood states (mood X time interaction, p<.001), with greater sadness in the negative mood conditions (both p<.001) but no difference between LPS and saline conditions. Significant main and interaction effects of inflammation and negative mood were observed for pain unpleasantness (all p<.05). During cued pain anticipation, a significant inflammation X mood interaction emerged for activation of the bilateral caudate nucleus and right hippocampus (all p_FWE<.05). Main effects of both inflammation and mood were observed in multiple regions, including insula, midcingulate cortex, prefrontal gyri, and hippocampus for inflammation, and midcingulate, caudate, and thalamus for mood (all p_FWE<0.05).

CONCLUSIONS

Results support an interplay of inflammation and sad mood on striatal and hippocampal circuitry engaged during visceral pain anticipation as well as on pain experience. This may reflect a nocebo mechanism, which may contribute to altered perception and interpretation of bodily signals. At the interface of affective neuroscience and the gut-brain axis, concurrent inflammation and negative mood may be vulnerability factors for chronic visceral pain.

Diffusion tensor imaging reveals sex differences in pain sensitivity of rats

Studies on differences in brain structure and function according to sex are reported to contribute to differences in behavior and cognition. However, few studies have investigated brain structures or used tractography to investigate gender differences in pain sensitivity. The identification of tracts involved in sex-based structural differences that show pain sensitivity has remained elusive to date. Here, we attempted to demonstrate the sex differences in pain sensitivity and to clarify its relationship with brain structural connectivity. In this study, pain behavior test and brain diffusion tensor imaging (DTI) were performed in male and female rats and tractography was performed on the whole brain using fiber tracking software. We selected eight brain regions related to pain and performed a tractography analysis of these regions. Fractional anisotropy (FA) measurements using automated tractography revealed sex differences in the anterior cingulate cortex (ACC)-, prefrontal cortex (PFC)-, and ventral posterior thalamus-related brain connections. In addition, the results of the correlation analysis of pain sensitivity and DTI tractography showed differences in mean, axial, and radial diffusivities, as well as FA. This study revealed the potential of DTI for exploring circuits involved in pain sensitivity. The behavioral and functional relevance's of measures derived from DTI tractography is demonstrated by their relationship with pain sensitivity.

The reward for placebos: mechanisms underpinning placebo-induced effects on motor performance

Different from the most popular thinking, the placebo effect is not a purely psychological phenomenon. A body of knowledge from multidisciplinary fields has shown that the expectation of a potential benefit when receiving a treatment induces a cascade of neurochemical-electrophysiological alterations in brain reward areas, including motor-related ones. Alterations in the dopamine, opioid, and glutamate metabolism are the neural representation converting reward-derived declarative forms into an attractive and wanted behavior, thereby changing the activation in reward subcortical and cortical structures involved in motor planning, motor execution, and emotional-cognitive attributes of decision-making. We propose that the expectation of receiving a treatment that is beneficial to motor performance triggers a cascade of activations in brain reward areas that travels from motor planning and motor command areas, passing through corticospinal pathways until driving the skeletal muscles, therefore facilitating the motor performance. Although alternative explanations cannot be totally ruled out, this mechanistic route is robust in explaining the results of placebo-induced effects on motor performance and could lead to novel insights and applications in the exercise sciences. Factors such as sex differences in reward-related mechanisms and aversion-induced nocebo effects should also be addressed.

Acupuncture modulates the frequency-specific functional connectivity density in primary dysmenorrhea

Background

The study aimed to investigate how acupuncture modulates brain activities across multiple frequency bands to achieve therapeutic effects in PDM.

Methods

A total of 47 patients with PDM were randomly assigned to the verum acupuncture group and sham acupuncture group with three menstrual cycles of the acupuncture course. The fMRI scans, visual analog scale (VAS) scores, and other clinical evaluations were assessed at baseline and after three menstrual-cycles treatments. The global functional connectivity density (gFCD) analyses were performed between the pre-and post-acupuncture course of two groups at full-low frequency band, Slow-3 band, Slow-4 band, and Slow-5 band.

Results

After the acupuncture treatments, the patients with PDM in the verum acupuncture group showed significantly decreased VAS scores (p &lt; 0.05). The frequency-dependent gFCD alternations were found in the verum acupuncture group, altered regions including DLPFC, somatosensory cortex, anterior cingulate cortex (ACC), middle cingulate cortex (MCC), precuneus, hippocampus, and insula. The sham acupuncture modulated regions including angular gyrus, inferior frontal gyrus, and hippocampus. The gFCD alternation in DLPFC at the Slow-5 band was negatively in the patients with PDM following verum acupuncture, and S2 at the Slow-4 band was positively correlated with VAS scores.

Conclusion

These findings supported that verum acupuncture could effectively modulate frequency-dependent gFCD in PDM by influencing abnormal DLPFC at Slow-5 band and hippocampus at the Slow-3 band. The outcome of this study may shed light on enhancing the potency of acupuncture in clinical practice.

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.