Pain affect encoded in human anterior cingulate but not somatosensory cortex

The impact of membrane receptors on modulating empathic pain

Humans can estimate each other's pain and provide adapted care to reduce it. Empathetic skills are crucial for caregivers involved in pain management; consequently, educational programs and theories have emphasized the positive role of empathy in reducing pain intensity. It is also widely assumed that if caregivers lack empathy, they will underestimate pain intensity in their patients, and this unempathetic attitude can negatively influence pain intensity perception. Empathy for pain is thought to activate the affective‒motivational components of the pain matrix, which includes the anterior insula, middle and anterior cingulate cortices and amygdala, as indicated by functional magnetic resonance imaging and other methodologies. Activity in this core neural network reflects the affective experience that activates our responses to pain and lays the neural foundation for our understanding of our own emotions and those of others. Additionally, a variety of factors can regulate the intensity of empathy for pain, such as oxytocin and vasopressin receptors. Therefore, we selectively review the molecular mechanisms by which membrane receptors modulate this pain modality.

Activation of NMDA Receptors in the Anterior Cingulate Cortex Enhances Anxiety-Induced Behaviour and Antinociception, and Contributes to the Modulation of Pain-Facilitatory Descending Pathways

BACKGROUND

The anterior cingulate cortex (ACC) is known to modulate glutamate-mediated fear-related defensive behaviours and nociceptive responses. However, its role in acute anxiety-related behaviours and associated antinociception remains unclear. This study aimed to investigate the involvement of the ACC in anxiety-induced responses and its potential descending pathways influencing spinal nociceptive processing.

METHODS

Male and female Wistar rats received microinjections of either vehicle or the NMDA receptor agonist N-methyl-D-aspartic acid (NMDA; 1 nmol) into area 24b (Cg1) of the ACC. Rats were then tested in the elevated plus maze (EPM) or open field (OF) tests, followed by the tail-flick test. In a separate experiment, anaesthetised rats were exposed to a thermal tail stimulus while undergoing electrophysiological recordings in the rostral ventromedial medulla (RVM) after ACC activation with NMDA. In some cases, NMDA administration was preceded by microinjections of vehicle or the NMDA receptor antagonist AP-5 (1 nmol) into the dorsal periaqueductal grey (dPAG), a midbrain site involved in descending pain modulation.

RESULTS

NMDA-induced activation of ACC area 24b increased anxiety-related behaviours and antinociception in males during both EPM and OF testing. In females, this effect was observed only in the EPM test. In anaesthetised rats, ACC activation facilitated spinal nociception, an effect abolished by dPAG NMDA receptor blockade, suggesting a relay through this midbrain region.

CONCLUSIONS

ACC activation enhances anxiety-related behaviour. While it promotes pronociception under anaesthesia, it induces antinociceptive effects in awake animals exposed to anxiogenic contexts.

Can EEG-Neurofeedback Training Enhance Effective Connectivity in People With Chronic Secondary Musculoskeletal Pain? A Secondary Analysis of a Feasibility Randomized Controlled Clinical Trial

INTRODUCTION

Persistent musculoskeletal pain is associated with altered functional and effective connectivity (EC) between cortical regions involved in pain processing. Especially, disruptions in the infraslow fluctuation (ISF) frequency band can contribute to pain persistence. ISF electroencephalography-neurofeedback (EEG-NF) has emerged as a potential non-invasive neuromodulatory intervention targeting cortical brain regions to restore balance and modulate pain-related pathways. However, limited research explores its effect on EC, a measure of directional information flow critical to pain experience and modulation.

METHODS

A secondary analysis was performed using data from a randomized, double-blind, sham-controlled feasibility clinical trial. Participants with chronic painful knee osteoarthritis (OA) were randomized to receive either ISF-NF or sham-NF. Nine neurofeedback sessions targeted the pregenual anterior cingulate cortex (pgACC), dorsal anterior cingulate cortex (dACC), and bilateral primary somatosensory cortex (SSC: S1Lt & S1Rt). EEG data was collected at baseline and post-intervention. Granger causality was used to measure EC changes, and between-group statistical analyses were conducted with adjustments for multiple comparisons.

RESULTS

Twenty-one participants (mean age: 61.7 ± 7.6 years; 62% female) completed the study. ISF-NF training significantly improved EC between pgACC and dACC, pgACC and SSC, and other targeted regions, while reducing EC from S1Rt to dACC. Changes were observed predominantly in the ISF frequency band, indicating enhanced cortical communication and modulation of pain pathways.

CONCLUSION

ISF-NF training enhanced EC in cortical regions implicated in pain processing, supporting its potential as a neuromodulatory intervention for chronic musculoskeletal pain. Further trials are needed to confirm clinical efficacy and optimize protocol designs.

Neural mechanisms, influencing factors and interventions in empathic pain

Empathic pain, defined as the emotional resonance with the suffering of others, is akin to the observer's own experience of pain and is vital for building and sustaining positive interpersonal relationships. Despite its importance, the neural mechanism of empathic pain remains poorly understood. In this review, we integrated and summarized the currently knowledge on the neural networks associated with empathic pain, focusing on key brain regions such as the insula, anterior cingulate cortex (ACC), ventral tegmental area (VTA), nucleus accumbens (NAc), and locus coeruleus (LC)/norepinephrine (NE)-sympatho-adrenomedullar (LC/NE-SAM) system. We also reviewed the factors that affect empathic pain, including gender, personal beliefs, the intimacy of relationships, and the nature of interpersonal relationships, and highlighted the central role of the insula and ACC in the neural circuitry of empathy, the importance of the IC-BLA and ACC-NAc/VTA connections in modulating empathic pain, and the involvement of the LC/NE-SAM system in mediating pain empathy. We further discussed how gender significantly influences empathic pain, with women showing more intense emotional reactions to social distress than men. It also summarized the roles of personal pain history and empathy levels in modulating empathic responses. Furthermore, the review emphasized the impact of social factors such as the nature of interpersonal relationships and experiences of social exclusion on empathic pain. By providing a detailed exploration of the neural mechanisms and influencing factors of empathic pain, this review aims to establish a robust foundation for developing targeted therapeutic strategies and improving pain management in clinical settings.

A plank across the explanatory gap: The case of pain

According to a widely shared belief, an explanation of phenomenal experience in terms of neural mechanisms is impossible in principle. The reason for this "Explanatory Gap" is supposed to be a basic incompatibility between phenomenal and neuroscientific knowledge: while the latter is framed in terms of functional relationships, it is impossible to capture phenomenal experience in functional terms. Here, we will take three steps to avert this conclusion and show what an explanation of the qualitative character of phenomenal experience might look like. In Step I, we show that two pivotal assumptions underlying the "Explanatory Gap" argument are unfounded. This means that the problem of phenomenal experience can be solved with the familiar methods of hypothesis development and testing. In Step II, we hypothesize that paradigmatic sorts of phenomenal experience like affective pain can be captured in functional terms, provided the function is framed in cognitive rather than behavioral terms: feeling affective pain is feeling an urge to avoid. In Step III, we will present empirical evidence corroborating this claim. We will also indicate how this functional description can help to identify the neural mechanisms underlying affective pain experience. We take this as a proof of principle showing that the qualitative character of phenomenal experience can be explained in objective neuroscientific terms. We will conclude with some remarks on how our approach might contribute to future progress in our understanding of consciousness in general.

Transcranial direct current stimulation in the management of pain in oncology patients. A systematic review and meta-analysis with meta-regression of randomized controlled trials

PURPOSE

To evaluate the efficacy of transcranial direct current stimulation (tDCS) in pain management in subjects with oncologic process.

MATERIAL AND METHODS

Several databases were searched in December 2023. Randomized Controlled Trials that evaluated the application of tDCS on pain in adults with oncologic process were selected. Random-effects meta-analysis with 95%CI were used to quantify the change scores in pain between tDCS and control groups.

RESULTS

Six trials with 482 participants were included. There were significant differences in favor of tDCS in pain intensity in surgical oncology patients compared to sham stimulation (p < 0.001). Non-surgical patients showed no significant effect. Meta-regression analysis in this group of patients showed that the timing of the evaluation moderated the effect of tDCS on pain (p= .042), with longer time after tDCS being associated with greater pain reduction.

CONCLUSIONS

The application of a-tDCS for at least 20 min, with a current density higher than 0.057 mA/cm2, applied over M1, left DLPFC, or the insula area, between 2-5 sessions appears to be an effective and safe treatment of pain in surgical oncology patients compared to sham. The tDCS appears to be more effective for high-intensity pain, and in the long term.

Targeting PI3K-mTOR signaling in the anterior cingulate cortex improves emotional behavior, and locomotor activity in rats with bone cancer pain

Objective

To investigate the effects of targeting the PI3K-mTOR signaling pathway in the anterior cingulate cortex (ACC) on pain responses, locomotor activity, and emotional behavior in rats with bone cancer pain.

Methods

Bone cancer pain was induced by implanting Walker 256 cells into the rat. Pain responses were assessed using paw withdrawal threshold and latency measurements, while locomotor activity and negative mood were evaluated through open field and conditioned place aversion tests, respectively.

Results

The results showed that the bone cancer pain model led to allodynia, hyperalgesia, decreased ambulation, and ACC microglial activation. Morphine treatment improved pain responses but did not affect locomotor activity or mTOR protein expression. In contrast, rapamycin treatment reduced pain, improved locomotor activity, and decreased negative mood. It also downregulated PI3K-mTOR protein expression. Furthermore, inhibiting the PI3K-mTOR pathway with a PI3K inhibitor or rapamycin not only improved pain responses and locomotor activity but also reduced depression and anxiety-like behaviors. These effects were accompanied by changes in paw withdrawal threshold, latency, static time, and PI3K-mTOR protein expression.

Conclusions

Targeting the PI3K-mTOR signaling pathway in the ACC effectively alleviates pain-related symptoms and emotional disturbances in rats with bone cancer pain. This approach holds promise for alleviating pain and allaying negative emotion after further study.

Opioidergic pain relief in humans is mediated by beta and high-gamma modulation in limbic regions

The nature of the neurophysiological effects of opioids, especially those responsible for their analgesic properties, are unknown, hindering efforts to develop non-addictive alternatives. Fentanyl and hydromorphone were administered to patients experiencing semi-chronic, clinically-relevant pain after surgical implantation of electrodes for the localization of seizure onset. Opioids suppressed beta oscillations in lateral amygdala, ventral and dorsolateral prefrontal cortices, and increased beta in medial amygdala and hippocampus. Opioids also suppressed high gamma oscillations in insula and lateral amygdala, and increased high gamma in cingulate cortex and hippocampus. The amplitude of these beta effects in the ventral prefrontal cortex, medial amygdala and hippocampus, and of gamma effects in the insula, were positively correlated with the magnitude of pain relief in response to a constant dose. These findings identify electrophysiological events in a network of limbic structures that may participate in opioidergic pain relief through nociceptive gating and a decreased concerned fixation on pain, providing insights into the neural basis of pain relief and suggesting possible biomarkers for developing non-addictive opioid alternatives.

Zingerone alleviates inflammatory pain by reducing the intrinsic excitability of anterior cingulate cortex neurons in a mice model

Background

Zingiber officinale Roscoe has been shown to possess analgesic properties. Zingerone (ZO), a bioactive compound derived from Zingiber officinale Roscoe, exhibits a range of pharmacological effects, including anti-inflammatory, anti-cancer, antioxidant, antibacterial, and anti-apoptotic activities. However, the analgesic properties of zingerone remain unclear.

Methods

Complete Freund's adjuvant (CFA) was administered to the left hind paw of C57BL/6 mice to induce a model of inflammatory pain. The analgesic effects of zingerone were assessed using the Von Frey and Hargreaves tests. In vivo fiber photometry and whole-cell patch clamp techniques were employed to investigate the potential mechanisms.

Results

Both acute and long-term treatment with zingerone resulted in a significant increase in mechanical and thermal pain thresholds in mice experiencing CFA-induced inflammatory pain. Mechanical stimulation led to a pronounced increase in calcium levels within the anterior cingulate cortex (ACC) neurons of the inflammatory pain model, which was alleviated by zingerone administration. Furthermore, zingerone was found to modify synaptic transmission to ACC neurons and decrease their intrinsic excitability by prolonging the refractory period of these neurons.

Conclusion

Zingerone demonstrates potential for alleviating CFA-induced inflammatory pain by reducing the intrinsic excitability of ACC neurons in a mouse model.

Identifying neural circuitry abnormalities in neuropathic pain with transcranial magnetic stimulation and electroencephalogram co-registration

Non-invasive brain stimulation (NIBS) technology such as transcranial magnetic stimulation (TMS) represents a promising treatment for neuropathic pain. However, neural circuitries underlying analgesia remain to be established, which is largely limiting treatment responses. Using TMS and electroencephalogram co-registration (TMS-EEG), this study quantified the circuitry abnormalities in neuropathic pain and their associations with pain symptoms. A group of 21 neuropathic pain individuals and 21 healthy controls were assessed with TMS-EEG delivering to the primary motor cortex (M1). With source modelling, local current density and current propagation were analysed with significant current density (SCD) and scattering (SCS) respectively. The SCS and SCD data converged on higher activities in neuropathic pain individuals than healthy controls, within the emotional affective (perigenual anterior cingulate cortex, pgACC), sensory nociceptive (primary somatosensory cortex, S1), and the attentional cognitive (anterior insula, aINS; supracallosal anterior cingulate cortex, scACC) structures of pain. Moreover, current propagation to the pgACC was associated with lower pain-related negative emotions, while current propagation to the aINS with higher pain-related negative emotions. Using concurrent TMS-EEG, our data identified abnormal pain circuitries that could be utilised to improve treatment efficacy with brain stimulation technologies.

Closed-Loop Infraslow Brain-Computer Interface can Modulate Cortical Activity and Connectivity in Individuals With Chronic Painful Knee Osteoarthritis: A Secondary Analysis of a Randomized Placebo-Controlled Clinical Trial

Introduction. Chronic pain is a percept due to an imbalance in the activity between sensory-discriminative, motivational-affective, and descending pain-inhibitory brain regions. Evidence suggests that electroencephalography (EEG) infraslow fluctuation neurofeedback (ISF-NF) training can improve clinical outcomes. It is unknown whether such training can induce EEG activity and functional connectivity (FC) changes. A secondary data analysis of a feasibility clinical trial was conducted to determine whether EEG ISF-NF training can significantly alter EEG activity and FC between the targeted cortical regions in people with chronic painful knee osteoarthritis (OA). Methods. A parallel, two-arm, double-blind, randomized, sham-controlled clinical trial was conducted. People with chronic knee pain associated with OA were randomized to receive sham NF training or source-localized ratio ISF-NF training protocol to down-train ISF bands at the somatosensory (SSC), dorsal anterior cingulate (dACC), and uptrain pregenual anterior cingulate cortices (pgACC). Resting state EEG was recorded at baseline and immediate post-training. Results. The source localization mapping demonstrated a reduction (P = .04) in the ISF band activity at the left dorsolateral prefrontal cortex (LdlPFC) in the active NF group. Region of interest analysis yielded significant differences for ISF (P = .008), slow (P = .007), beta (P = .043), and gamma (P = .012) band activities at LdlPFC, dACC, and bilateral SSC. The FC between pgACC and left SSC in the delta band was negatively correlated with pain bothersomeness in the ISF-NF group. Conclusion. The EEG ISF-NF training can modulate EEG activity and connectivity in individuals with chronic painful knee osteoarthritis, and the observed EEG changes correlate with clinical pain measures.

Consciousness Research Through Pain

Background/Objectives: Consciousness is a complex and elusive phenomenon encompassing self-awareness, sensory perception, emotions, and cognition. Despite significant advances in neuroscience, understanding the neural mechanisms underlying consciousness remains challenging. Pain, as a subjective and multifaceted experience, offers a unique lens for exploring consciousness by integrating sensory inputs with emotional and cognitive dimensions. This study examines the relationship between consciousness and pain, highlighting the potential of pain as a model for understanding the interplay between subjective experience and neural activity. Methods: Literature review. Results: Key theories of consciousness, such as the Global Workspace Theory and the Integrated Information Theory, provide diverse frameworks for interpreting the emergence of consciousness. Similarly, pain research emphasizes the role of subjective interpretation and emotional context in shaping sensory experiences, reflecting broader challenges in consciousness studies. The limitations of current methodologies, particularly the difficulty of objectively measuring subjective phenomena, like pain and consciousness, are also addressed. This highlights the importance of neural correlates, with a particular focus on brain regions, such as the anterior cingulate cortex and the insula, which bridge sensory and emotional experiences. By analyzing the shared attributes of pain and consciousness, this study underscores the potential for pain to serve as a measurable proxy in consciousness research. Conclusions: Ultimately, it contributes to unraveling the neural and philosophical underpinnings of consciousness, offering implications for mental health treatment and advancements in artificial intelligence. This study fills a critical gap by leveraging pain as a measurable and reproducible model for exploring the neural and subjective mechanisms of consciousness. By combining theoretical frameworks with empirical evidence, it offers novel insights into how consciousness emerges from neural processes.

The neural correlates of guilt highlight preclinical manifestations between bipolar and major depressive disorders

BACKGROUND

Over 25 % of bipolar disorder (BD) patients are misdiagnosed with major depressive disorder (MDD). An urgent need exists for a biomarker to differentiate BD from MDD. Various manifestations and intensities of maladaptive guilt processing might uniquely contribute to the pathogenesis of BD compared to MDD.

METHOD

This study adopted a first-person perspective guilt-provoking functional magnetic resonance imaging (fMRI) task, respectively induced by painful and ambiguous scenarios in 111 individuals: 35 with remitted MDD, 38 with remitted bipolar I disorder (BD-I), and 38 matched controls.

RESULTS

A significant interaction between group and sense of agency in predicting guilt ratings for ambiguous, rather than painful, scenarios. The association between sense of agency and guilt was significant in MDD but not in BD-I patients or controls. Activation in the dorsomedial prefrontal cortex (dmPFC), pregenual anterior cingulate cortex (pgACC), and right inferior parietal lobule (IPL) was higher in BD-I than MDD subjects in response to ambiguous scenarios, whereas these were comparable to painful ones. The correlation between guilt ratings and activation in the dorsal anterior cingulate cortex (dACC) to ambiguous scenarios was significant in MDD, but not in BD-I or controls. The results of the multivariate pattern classification analysis showed that in the ambiguous scenarios, the accuracy of using brain activation patterns in the dmPFC, pgACC, and IPL to distinguish between participants with MDD and BD-I was 70.0 %, 71.5 %, and 68.7 %, respectively. An additional test of the classification model, employing a combined mask of the three ROIs to distinguish between the two mood disorders in ambiguous scenarios, achieved an accuracy of 78.6 % and an AUC value of 0.84.

CONCLUSIONS

Subjective reports and neural correlates of guilt in ambiguous social situations, as well as a sense of agency, could provide to be a potential biomarker to help distinguish between BD-I and MDD even in the remitted stage.

When group grievances become personal: The neural correlates of group and personal rejection

Witnessing rejection against one's group can have similar impacts on psychological distress and aggression as experiencing rejection personally. In this study, we investigated the neural activity patterns of group rejection and whether they resemble those of personal-level rejection. We first identified the neural correlates of social rejection (exclusion based on negative attention) compared with ostracism (exclusion based on lack of social connection) and then compared group-level to personal-level rejection. We employed a novel social exclusion task, "RateME," to induce group and personal rejection and Cyberball to evoke ostracism during fMRI scans. Our results showed that personal rejection increased activity in regions associated with autobiographical memory and self-identity, such as the dorsomedial prefrontal cortex and the lingual gyrus, whereas ostracism engaged areas related to social pain and salience, including the anterior cingulate cortex and the insula. Additionally, group and personal-level rejection elicited similar neural activity patterns, regardless of participants' fusion with the rejected groups. Therefore, group membership seems sufficient for group rejection to trigger self-referential processing pathways similar to those activated by personal rejection. Our findings highlight the overlapping neural mechanisms underlying personal and group-level grievances, which may explain the detrimental effects of group rejection on aggression, extremism, and intergroup conflict.

Mild hypohydration in healthy older adults increases pain-related brain activity without affecting pain perception: a single-blind study

Understanding how hydration status influences pain perception is particularly important in older adults, as both dehydration and pain are prevalent in this population. Ten individuals (70 ± 4 yr) completed two randomized and counterbalanced trials. They were exposed to passive heat until they lost 1% body mass through sweat and urine (∼100 min), with the loss either unreplaced (sham infusion, HYPO) or fully replaced via 0.45% saline infusion (EUH). Nociceptive electrical stimulation was applied to the sural nerve 1) before heat exposure (baseline), 2) 60 min following hydration manipulation (R60, ∼160 min after baseline), 3) after mouth rinsing with water (MR, ∼170 min after baseline), and 4) following water ingestion (ING, ∼185 min after baseline). Pain-related event-related potentials were assessed using electroencephalography (EEG) at R60, MR, and ING. After hydration manipulation, body mass loss and plasma osmolality were greater, and plasma volumes were lower in HYPO than in EUH, although thirst did not differ between the conditions. There were no differences between the two conditions regarding pain intensity and unpleasantness. Still, EEG analyses revealed that the peak-to-peak amplitude of the pain-related N200-P300 potential (∼136-310 ms) was significantly greater in HYPO than in EUH (P = 0.036) and significantly greater in R60 compared with both MR (P = 0.01) and ING (P = 0.03), either with HYPO and EUH. These results suggest that mild hypohydration in healthy older adults may influence some neurophysiological processes related to nociception without significantly affecting pain perception.NEW & NOTEWORTHY This study reveals, for the first time, that mild hypohydration equivalent to ∼1% of body mass does not alter pain perception in healthy older adults when they are blinded to their hydration status, despite electroencephalography signals showing modulation of pain-related brain responses.

The endocannabinoid system in the brain undergoes long-lasting changes following neuropathic pain

The endocannabinoid system (ECS), which is composed of endocannabinoids (eCBs), cannabinoid receptors (CBRs), and associated signaling molecules, has been identified within the brain. In neuropathic pain animal models and patients, long-lasting alterations in the ECS have been observed. These changes of neurons and glial cells in the ECS contribute to the modulation of neuropathic pain. Intervention strategies such as the activation of CBRs, the enhancement of hydrolytic enzyme function, and the inhibition of synthetizing enzymes typically alleviate neuropathic pain through CBR-dependent mechanisms. Additionally, emotions such as fear, anxiety, and depression are frequently experienced with neuropathic pain. Exogenous cannabinoids can mitigate these mood disorders via CBR signaling pathways. Therefore, the targeting of long-lasting ECS alterations represents a potential therapeutic approach for both neuropathic pain and emotional disorders. In this review, the long-lasting variations in neurons and glial cells in the ECS related to neuropathic pain and the accompanying emotional comorbidities are elucidated. Furthermore, the cellular and molecular mechanisms underlying synaptic plasticity and neural circuit activities in the brain are reviewed.

Pain Management in Surgical Treatment of Facial Fractures: Alternative Approaches to Opioid Use

Study Design

Literature review.

Objective

This review aims to explore current opioid use trends for surgical management of facial fractures, as well as methods and alternative treatments to decrease opioid use.

Methods

Review of selected literature from Medline and Google Scholar.

Results

Despite the devastating effects of the opioid epidemic and recent policy changes aimed at reducing unnecessary opioid prescription, opioids remain commonly used for pain management after facial fracture repair. Recently, use of multimodal analgesic therapy has been suggested to decrease opioid dosage utilized for post-operative pain control. Alternatives to medication therapies have been proposed for pain management; however, standardized recommendations for pain management in facial fracture patients remain unclear.

Conclusions

Further research is required to establish evidence-based recommendations for pain management in craniofacial fracture repair.

Neuroscience of the human thalamus related to acute pain and chronic "thalamic" pain

The association of posterior thalamic strokes with the presence of chronic "thalamic" pain was described in the early 1900s and revisited in a recent review of these patients. Acute pain in corporal structures is associated with the spinothalamic tract (STT), which originates in the dorsal horn of the spinal cord, whereas that associated with cranial structures is associated with the spinal division of the trigeminal nucleus. These pathways terminate in the ventral posterior nucleus (VP), including its posterior and inferior subnuclei and its core, which is classically associated with tactile and haptic functions. In medial nuclei (medial dorsal and intralaminar) receptive fields are large and stimulation evokes diffuse unpleasant sensations and pain while neurons in these nuclei subserve cognitive processes of attention, alerting, and conditioning. In the lateral nuclei neurons have small receptive and projected fields and high resolution of responses to somatic stimuli. Neurons in the lateral nuclei respond to stimuli producing pain, temperature, and visceral sensations while stimulation evokes similar sensations. Small strokes in VP core versus structures located inferior and posterior are associated with thalamic pain and decreased tactile, painful, and cold sensations and with decreased evoked potentials for painful (laser) heat and median nerve stimulation (electrical). Lesions of VP, but not ventral medial posterior nucleus (VMpo), are associated with thalamic pain, contrary to the recent "disinhibition" model. We review the evidence that the lateral nuclei are associated with multiple processes including tactile, nociceptive, visceral, and thermal content of stimuli, whereas the medial nuclei are related to cognitions about those stimuli.

Sensory and affective dimensions in loudness perception: Insights from young adults

Traditional psychoacoustic measures often lack accuracy in diagnosing hyperacusis and other sound tolerance disorders, possibly due to their reliance on artificial stimuli and unidimensional scales. The aim of this study was to assess loudness across sensory and affective dimensions using natural sounds, drawing on pain research wherein intensity and unpleasantness are assessed separately. We hypothesized that similar distinctions apply to loudness perception. A total of 102 young adults with normal to mild hearing loss rated 32 sound stimuli (pleasant, unpleasant, neutral, and artificial) at 10 intensities (40 to 100 dBA) on sensory and affective scales. They also completed the Hyperacusis Questionnaire, the Noise Sensitivity Scale, and the Hospital Anxiety and Depression Scale. Mixed linear models indicated both correlations and dissociations between scales that varied according to intensity and valence. Louder stimuli were rated as more unpleasant, but only at high intensities. On the sensory scale, sounds were perceived as louder with increasing intensity; however, at low to moderate intensities, pleasant and neutral sounds were rated as louder, whereas at higher intensities, artificial and unpleasant stimuli were rated as louder. On the affective scale, the perception of unpleasantness also increased with intensity, but less steeply. At high intensities, artificial stimuli were rated similarly to unpleasant stimuli. Noise sensitivity scores predicted louder and more unpleasant ratings, whereas depression scores were associated with softer and less pleasant perceptions. This study highlights the need for multidimensional approaches in audiology and suggests that the integration of sensory and affective scales with natural stimuli may improve the diagnosis and treatment of sound tolerance disorders.

Neuroanatomy of the nociceptive system: From nociceptors to brain networks

This chapter reviews the neuroanatomy of the nociceptive system and its functional organization. We describe three main compartments of the nervous system that underlie normal nociception and the resulting pain percept: Peripheral, Spinal Cord, and Brain. We focus on how ascending nociceptive processing streams traverse these anatomical compartments, culminating in the multidimensional experience of pain. We also describe neuropathic pain conditions, in which nociceptive processing is abnormal, not only because of the primary effects of a lesion or disease affecting peripheral nerves or the central nervous system (CNS), but also due to secondary effects on ascending pathways and brain networks. We discuss how the anatomical components (circuits/networks) reorganize under various etiologies of neuropathic pain and how these changes can give rise to pathological pain states.

It all began in Issaquah 50 years ago

ABSTRACT

"Somehow scientists still pursue the same questions, if now on higher levels of theoretical abstraction rooted in deeper layers of empirical evidence… To paraphrase an old philosophy joke, science is more like it is today than it has ever been. In other words, science remains as challenging as ever to human inquiry. And the need to communicate its progress… remains as essential now as then." - Tom Siegfried, Science News 2021In fact, essential questions about pain have not changed since IASP's creation in Issaquah: what causes it and how can we treat it? Are we any closer to answering these questions, or have we just widened the gap between bench and bedside? The technology used to answer questions about pain mechanisms has certainly changed, whether the focus is on sensory neurons, spinal cord circuitry, descending controls or cortical pain processing. In this paper, we will describe how transgenics, transcriptomics, optogenetics, calcium imaging, fMRI, neuroimmunology and in silico drug development have transformed the way we examine the complexity of pain processing. But does it all, as our founders hoped, help people with pain? Are voltage-gated Na channels the new holy grail for analgesic development, is there a pain biomarker, can we completely replace opioids, will proteomic analyses identify novel targets, is there a "pain matrix," and can it be targeted? Do the answers lie in our tangible discoveries, or in the seemingly intangible? Our founders could barely imagine what we know now, yet their questions remain.

Multimodal benefits of hypnosis on pain, mental health, sleep, and quality of life in patients with chronic pain related to fibromyalgia: A randomized, controlled, blindly-evaluated trial

BACKGROUND AND PURPOSE

Fibromyalgia is a chronic syndrome marked by intense musculoskeletal pain often refractory to pharmacological treatment. Although studies have shown that hypnosis improves fibromyalgia pain, gaps in experimental design limit their reliability. This work aimed to evaluate the effects of hypnosis on pain, mental health, sleep, and quality of life in participants with fibromyalgia chronic pain.

METHODS

In this prospective, parallel, randomized, controlled, blindly-evaluated trial, participants of both sexes (n = 49) diagnosed with fibromyalgia and with moderate to severe chronic pain attended 8 weekly 1-h sessions with a hypnotherapist. For the hypnosis group (n = 24), sessions consisted in induction of hypnotic trance followed by suggestions to promote analgesia. For the control group (n = 25), sessions consisted in casual unscripted conversation. Participants were assessed at baseline (7 days before), post-intervention (7 days after), and follow-up (3 months after). The primary outcome was pain intensity. The secondary outcomes were the sensory and affective dimensions of pain; pain unpleasantness; pain catastrophizing; anxiety and depression; sleep quality; fibromyalgia impact; and quality of life.

RESULTS

Hypnosis significantly reduced pain scores both at post-intervention and follow-up in comparison with baseline. The analgesic effect of hypnosis combined with pharmacological treatment lasted for at least 3 months and was superior to analgesia promoted by first- and second-line pharmacological treatment alone. Hypnosis significantly improved all parameters evaluated as secondary outcomes both at post-intervention and follow-up without inducing adverse events.

CONCLUSION

Our results corroborate that clinical hypnosis is an effective and feasible tool for managing chronic pain and other symptoms of fibromyalgia.

Advances and challenges in neuroimaging-based pain biomarkers

Identifying neural biomarkers of pain has long been a central theme in pain neuroscience. Here, we review the state-of-the-art candidates for neural biomarkers of acute and chronic pain. We classify these potential neural biomarkers into five categories based on the nature of their target variables, including neural biomarkers of (1) within-individual perception, (2) between-individual sensitivity, and (3) discriminability for acute pain, as well as (4) assessment and (5) prospective neural biomarkers for chronic pain. For each category, we provide a synthesized review of candidate biomarkers developed using neuroimaging techniques including functional magnetic resonance imaging (fMRI), structural magnetic resonance imaging (sMRI), and electroencephalography (EEG). We also discuss the conceptual and practical challenges in developing neural biomarkers of pain. Addressing these challenges, optimal biomarkers of pain can be developed to deepen our understanding of how the brain represents pain and ultimately help alleviate patients' suffering and improve their well-being.

The different impacts of pain-related negative emotion and trait negative emotion on brain function in patients with inflammatory bowel disease

Inflammatory bowel diseases (IBD) are a group of chronic, non-specific intestinal diseases that could comorbid with varieties of negative emotional constructs, including pain-related negative emotions and trait negative emotions; however, the link between brain functions and different dimensions of negative emotions remains largely unknown. Ninety-eight patients with IBD and forty-six healthy subjects were scanned using a 3.0-T functional magnetic resonance imaging scanner. The amplitudes of low-frequency fluctuation (ALFF), regional homogeneity (ReHo), and degree centrality (DC) were used to assess resting-state brain activity. Partial least squares (PLS) correlation was employed to assess the relationship among abnormal brain activities, pain-related and trait negative emotions. Compared to controls, patients with IBD exhibited higher values of ALFF in the right anterior cingulate cortex (ACC), lower values of ALFF in the left postcentral gyrus, and higher values of DC in the bilateral ACC. Multivariate PLS correlation analysis revealed the brain scores of the ACC were correlated with pain-related negative emotions, the brain salience in the left postcentral gyrus was associated with the higher-order trait depression. These findings can enhance our comprehension of how pain-related negative emotion and trait negative emotion affect the brains of patients with IBD in distinct ways.

Neuromodulation for Neuropathic Pain Syndromes

OBJECTIVE

This article reviews the principles, applications, and emerging trends of neuromodulation as a therapeutic approach for managing painful neuropathic diseases. By parsing evidence for possible mechanisms of action and clinical trial outcomes for various diseases, this article focuses on five common therapy modalities: cutaneous, peripheral nerve, spinal cord, and brain stimulation, and intrathecal drug delivery.

LATEST DEVELOPMENTS

Recent advances in both invasive and noninvasive neuromodulation for pain have introduced personalized and closed-loop techniques, integrating real-time feedback mechanisms and combining therapies to improve physical and psychosocial function. Novel stimulation waveforms may influence distinct neural tissues to rectify pathologic pain signaling.

ESSENTIAL POINTS

With appropriate patient selection, peripheral nerve stimulation or epidural stimulation of the spinal cord can provide enduring relief for a variety of chronic pain syndromes. Newer technology using high frequencies, unique waveforms, or closed-loop stimulation may have selective advantages, but our current understanding of therapy mechanisms is very poor. For certain diagnoses and patients who meet clinical criteria, neuromodulation can provide profound, long-lasting relief that significantly improves quality of life. While many therapies are supported by data from large clinical trials, there is a risk of bias as most clinical studies were funded by device manufacturers or insurance companies, which increases the importance of real-world data analysis. Emerging methods like invasive or noninvasive brain stimulation may help us dissect basic mechanisms of pain processing and hold promise for personalized therapies for refractory pain syndromes. Finally, intrathecal delivery of drugs directly to segments of the spinal cord can also modify pain signaling to provide therapy for severe pain syndromes.

Anterior cingulate cortex-related functional hyperconnectivity underlies sensory hypersensitivity in Grin2b-mutant mice

Sensory abnormalities are observed in ~90% of individuals with autism spectrum disorders (ASD), but the underlying mechanisms are poorly understood. GluN2B, an NMDA receptor subunit that regulates long-term depression and circuit refinement during brain development, has been strongly implicated in ASD, but whether GRIN2B mutations lead to sensory abnormalities remains unclear. Here, we report that Grin2b-mutant mice show behavioral sensory hypersensitivity and brain hyperconnectivity associated with the anterior cingulate cortex (ACC). Grin2b-mutant mice with a patient-derived C456Y mutation (Grin2bC456Y/+) show sensory hypersensitivity to mechanical, thermal, and electrical stimuli through supraspinal mechanisms. c-fos and functional magnetic resonance imaging indicate that the ACC is hyperactive and hyperconnected with other brain regions under baseline and stimulation conditions. ACC pyramidal neurons show increased excitatory synaptic transmission. Chemogenetic inhibition of ACC pyramidal neurons normalizes ACC hyperconnectivity and sensory hypersensitivity. These results suggest that GluN2B critically regulates ASD-related cortical connectivity and sensory brain functions.

Understanding inter-individual variability of experimental pain habituation and conditioned pain modulation in healthy individuals

Although reduced experimental pain habituation is proposed as a proxy of diminished endogenous pain modulatory capacity in chronic pain, prior studies show contradictory findings. Even across healthy participants, pain habituation varies substantially, which may relate to another measure of endogenous pain modulation, i.e., conditioned pain modulation (CPM). Hence, this study investigated the relationship between pain habituation and CPM. Pain habituation was assessed in 45 healthy participants between two blocks of 15-20 contact-heat stimuli applied to the hand. Habituation of subjective pain ratings and objective neurophysiological readouts (contact-heat evoked potential (CHEP) and palmar sympathetic skin response (SSR)) was investigated. CPM was assessed by comparing heat pain thresholds before and after hand immersion in a noxious cold (9 °C) and lukewarm water bath (32 °C, to control for repeated measures effects). Pain habituation showed a large variability, with subjective but not objective pain habituation correlating with cold-induced CPM effects (r = 0.50; p = 0.025). This correlation was not observed for 'true' CPM effects (corrected for repeated measures effects) nor for CPM effects induced by a lukewarm water bath. These findings suggest that the observed variability in subjective pain habituation may be influenced by both descending endogenous pain modulation and peripheral adaptation processes associated with repeated measures. Objective pain habituation readouts, i.e., CHEPs and SSRs, capture different, complementary aspects of endogenous pain modulation.

Pain anticipation is a new behavioural sign of minimally conscious state

Probing cognition and consciousness in the absence of functional communication remains an extremely challenging task. In this perspective, we imagined a basic clinical procedure to explore pain anticipation at bedside. In a series of 61 patients with a disorder of consciousness, we tested the existence of a nociceptive anticipation response by pairing a somaesthetic stimulation with a noxious stimulation. We then explored how nociceptive anticipation response correlated with (i) clinical status inferred from Coma Recovery Scale-Revised scoring, (ii) with an EEG signature of stimulus anticipation-the contingent negative variation-and (iii) how nociceptive anticipation response could predict consciousness outcome at 6 months. Proportion of nociceptive anticipation response differed significantly according to the state of consciousness: nociceptive anticipation response was present in 5 of 5 emerging from minimally conscious state patients (100%), in 10 of 11 minimally conscious state plus patients (91%), but only in 8 of 17 minimally conscious state minus patients (47%), and only in 1 of 24 vegetative state/unresponsive wakefulness syndrome patients (4%) (χ 2  P < 0.0001). Nociceptive anticipation response correlated with the presence of a contingent negative variation, suggesting that patients with nociceptive anticipation response were more prone to actively expect and anticipate auditory stimuli (Fisher's exact test P = 0.05). However, nociceptive anticipation response presence did not predict consciousness recovery. Nociceptive anticipation response appears as a new additional behavioural sign that can be used to differentiate minimally conscious state from vegetative state/unresponsive wakefulness syndrome patients. As most behavioural signs of minimally conscious state, the nociceptive anticipation response seems to reveal the existence of a cortically mediated state that does not necessarily reflect residual conscious processing.

A computational mechanism of cue-stimulus integration for pain in the brain

The brain integrates information from pain-predictive cues and noxious inputs to construct the pain experience. Although previous studies have identified neural encodings of individual pain components, how they are integrated remains elusive. Here, using a cue-induced pain task, we examined temporal functional magnetic resonance imaging activities within the state space, where axes represent individual voxel activities. By analyzing the features of these activities at the large-scale network level, we demonstrated that overall brain networks preserve both cue and stimulus information in their respective subspaces within the state space. However, only higher-order brain networks, including limbic and default mode networks, could reconstruct the pattern of participants' reported pain by linear summation of subspace activities, providing evidence for the integration of cue and stimulus information. These results suggest a hierarchical organization of the brain for processing pain components and elucidate the mechanism for their integration underlying our pain perception.

Exercise-induced pain within endurance exercise settings: Definitions, measurement, mechanisms and potential interventions

Pain can be defined as an unpleasant sensory and emotional experience associated with or resembling that associated with actual or potential tissue damage. Though consistent with this definition, different types of pain result in different behavioural and psychophysiological responses. For example, the transient, non-threatening, acute muscle pain element of exercise-induced pain (EIP) is entirely different from other pain types like delayed onset muscle soreness, muscular injury or chronic pain. However, studies often conflate the definitions or assume parity between distinct pain types. Consequently, the mechanisms through which pain might impact exercise behaviour across different pain subcategories may be incorrectly assumed, which could lead to interventions or recommendations that are inappropriate. Therefore, this review aims to distinguish EIP from other subcategories of pain according to their aetiologies and characteristics, thereby providing an updated conceptual and operational definition of EIP. Secondly, the review will discuss the experimental pain models currently used across several research domains and their relevance to EIP with a focus on the neuro-psychophysiological mechanisms of EIP and its effect on exercise behaviour and performance. Finally, the review will examine potential interventions to cope with the impact of EIP and support wider exercise benefits. HIGHLIGHTS: What is the topic of this review? Considerations for future research focusing on exercise-induced pain within endurance exercise settings. What advances does it highlight? An updated appraisal and guide of research concerning exercise-induced pain and its impact on endurance task behaviour, particularly with reference to the aetiology, measurement, and manipulation of exercise-induced pain.

Expectation of pain and relief: A dynamical model of the neural basis for pain-trauma co-morbidity

Posttraumatic Stress Disorder (PTSD) is highly co-morbid with chronic pain conditions. When present, PTSD significantly worsens chronic pain outcomes. Likewise, pain contributes to a more severe PTSD as evidenced by greater disability, more frequent use of harmful opioid analgesics and increased pain severity. The biomechanism behind this comorbidity is incompletely understood, however recent work strongly supports the widely-accepted role of expectation, in the entanglement of chronic pain and trauma symptoms. This work has shown that those with trauma have a maladaptive brain response while expecting stress and pain, whereas those with chronic pain may have a notable impairment in brain response while expecting pain relief. This dynamical expectation model of the interaction between neural systems underlying expectation of pain onset (traumatic stress) and pain offset (chronic pain) is biologically viable and may provide a biomechanistic insight into pain-trauma comorbidity. These predictive mechanisms work through interoceptive pathways in the brain critically the insula cortex. Here we highlight how the neural expectation-related mechanisms augment the existing models of pain and trauma to better understand the dynamics of pain and trauma comorbidity. These ideas will point to targeted complementary clinical approaches, based on mechanistically separable neural biophenotypes for the entanglement of chronic pain and trauma symptoms.

Age-related differences in functional connectivity associated with pain modulation

Growing evidence suggests that aging is associated with impaired endogenous pain modulation, and that this likely underlies the increased transition from acute to chronic pain in older individuals. Resting-state functional connectivity (rsFC) offers a valuable tool to examine the neural mechanisms behind these age-related changes in pain modulation. RsFC studies generally observe decreased within-network connectivity due to aging, but its relevance for pain modulation remains unknown. We compared rsFC within a set of brain regions involved in pain modulation between young and older adults and explored the relationship with the efficacy of distraction from pain. This revealed several age-related increases and decreases in connectivity strength. Importantly, we found a significant association between lower pain relief and decreased strength of three connections in older adults, namely between the periaqueductal gray and right insula, between the anterior cingulate cortex (ACC) and right insula, and between the ACC and left amygdala. These findings suggest that the functional integrity of the pain control system is critical for effective pain modulation, and that its function is compromised by aging.

Acute and Long-Term Effects of App-Delivered Heartfulness Meditation on Psychological Outcomes and the Endocannabinoid Signaling System in Cyclic Vomiting Syndrome

INTRODUCTION

Cyclic vomiting syndrome (CVS) is a disorder of gut-brain interaction often triggered by stress. Interventions such as meditation may improve psychological outcomes and health-related quality of life (HRQoL), but their efficacy and the underlying mechanism are unknown.

METHODS

We conducted a 6-week single-arm pilot study to assess the effects of heartfulness meditation (HFM) in CVS using a custom-designed meditation app. Primary outcomes included state and trait anxiety and mood state changes pre vs post-meditation, and secondary outcomes were psychological distress, coping, sleep quality, and HRQoL at baseline and at weeks 3 and 6. Serum concentrations of endocannabinoids N -arachidonylethanolamine and 2-arachidonoylglycerol and related lipids were measured pre- and post-HFM at baseline and week 6.

RESULTS

In 30 treatment completers, there was a significant improvement in state anxiety ( P < 0.001), total mood disturbance ( P < 0.001), and other mood states (all P values < 0.05) across the 3 time points. Trait anxiety was also improved at week 6. There was a significant improvement in psychological distress (Global Severity Index), sleep quality (daytime dysfunction), coping (using religion/spirituality), and HRQoL (mental and physical) across the 3 time points (all P < 0.05). Significant increases in N -arachidonylethanolamine and related lipids N -oleoylethanolamine and palmitoylethanolamide post vs pre-HFM were observed at week 6 ( P < 0.001, 0.002, 0.003, respectively). No adverse effects were noted.

DISCUSSION

App-delivered HFM is feasible, safe, and effective and improves psychological outcomes and augments endocannabinoids. This provides insight into the mechanism underlying HFM and has potential for widespread use as a digital therapeutic in CVS and other disorder of gut-brain interaction.

Causal interactions in brain networks predict pain levels in trigeminal neuralgia

Trigeminal neuralgia (TN) is a highly debilitating facial pain condition. Magnetic resonance imaging (MRI) is the main method for generating insights into the central mechanisms of TN pain in humans. Studies have found both structural and functional abnormalities in various brain structures in TN patients as compared with healthy controls. Whereas studies have also examined aberrations in brain networks in TN, no studies have to date investigated causal interactions in these brain networks and related these causal interactions to the levels of TN pain. We recorded fMRI data from 39 TN patients who either rested comfortably in the scanner during the resting state session or tracked their pain levels during the pain tracking session. Applying Granger causality to analyze the data and requiring consistent findings across the two scanning sessions, we found 5 causal interactions, including: (1) Thalamus → dACC, (2) Caudate → Inferior temporal gyrus, (3) Precentral gyrus → Inferior temporal gyrus, (4) Supramarginal gyrus → Inferior temporal gyrus, and (5) Bankssts → Inferior temporal gyrus, that were consistently associated with the levels of pain experienced by the patients. Utilizing these 5 causal interactions as predictor variables and the pain score as the predicted variable in a linear multiple regression model, we found that in both pain tracking and resting state sessions, the model was able to explain ∼36 % of the variance in pain levels, and importantly, the model trained on the 5 causal interaction values from one session was able to predict pain levels using the 5 causal interaction values from the other session, thereby cross-validating the models. These results, obtained by applying novel analytical methods to neuroimaging data, provide important insights into the pathophysiology of TN and could inform future studies aimed at developing innovative therapies for treating TN.

Claustrum projections to the anterior cingulate modulate nociceptive and pain-associated behavior

The anterior cingulate cortex (ACC) is critical for the perception and unpleasantness of pain.1,2,3,4,5,6 It receives nociceptive information from regions such as the thalamus and amygdala and projects to several cortical and subcortical regions of the pain neuromatrix.7,8 ACC hyperexcitability is one of many functional changes associated with chronic pain, and experimental activation of ACC pyramidal cells produces hypersensitivity to innocuous stimuli (i.e., allodynia).9,10,11,12,13,14 A less-well-studied projection to the ACC arises from a small forebrain region, the claustrum.15,16,17,18,19,20 Stimulation of excitatory claustrum projection neurons preferentially activates GABAergic interneurons, generating feed-forward inhibition onto excitatory cortical networks.21,22,23,24 Previous work has shown that claustrocingulate projections display altered activity in prolonged pain25,26,27; however, it remains unclear whether and how the claustrum participates in nociceptive processing and high-order pain behaviors. Inhibition of ACC activity reverses mechanical allodynia in animal models of persistent and neuropathic pain,1,9,28 suggesting claustrum inputs may function to attenuate pain processing. In this study, we sought to define claustrum function in acute and chronic pain. We found enhanced claustrum activity after a painful stimulus that was attenuated in chronic inflammatory pain. Selective inhibition of claustrocingulate projection neurons enhanced acute nociception but blocked pain learning. Inversely, chemogenetic activation of claustrocingulate neurons had no effect on basal nociception but rescued inflammation-induced mechanical allodynia. Together, these results suggest that claustrocingulate neurons are a critical component of the pain neuromatrix, and dysregulation of this connection may contribute to chronic pain.

Effects of functional polymorphisms of opioid receptor mu 1 and catechol-O-methyltransferase on the neural processing of pain

AIM

Pain is reconstructed by brain activities and its subjectivity comes from an interplay of multiple factors. The current study aims to understand the contribution of genetic factors to the neural processing of pain. Focusing on the single-nucleotide polymorphism (SNP) of opioid receptor mu 1 (OPRM1) A118G (rs1799971) and catechol-O-methyltransferase (COMT) val158met (rs4680), we investigated how the two pain genes affect pain processing.

METHOD

We integrated a genetic approach with functional neuroimaging. We extracted genomic DNA information from saliva samples to genotype the SNP of OPRM1 and COMT. We used a percept-related model, in which two different levels of perceived pain intensities ("low pain: mildly painful" vs "high pain: severely painful") were employed as experimental stimuli.

RESULTS

Low pain involves a broader network relative to high pain. The distinct effects of pain genes were observed depending on the perceived pain intensity. The effects of low pain were found in supramarginal gyrus, angular gyrus, and anterior cingulate cortex (ACC) for OPRM1 and in middle temporal gyrus for COMT. For high pain, OPRM1 affected the insula and cerebellum, while COMT affected the middle occipital gyrus and ACC.

CONCLUSION

OPRM1 primarily affects sensory and cognitive components of pain processing, while COMT mainly influences emotional aspects of pain processing. The interaction of the two pain genes was associated with neural patterns coding for high pain and neural activation in the ACC in response to pain. The proteins encoded by the OPRM1 and COMT may contribute to the firing of pain-related neurons in the human ACC, a critical center for subjective pain experience.

Myeloid Cell Association with Spinal Cord Injury-Induced Neuropathic Pain and Depressive-like Behaviors in LysM-eGFP Mice

Spinal cord injury (SCI) affects ∼500,000 people worldwide annually, with the majority developing chronic neuropathic pain. Following SCI, approximately 60% of these individuals are diagnosed with comorbid mood disorders, while only ∼21% of the general population will experience a mood disorder in their lifetime. We hypothesize that nociceptive and depressive-like dysregulation occurs after SCI and is associated with aberrant macrophage infiltration in segmental pain centers. We completed moderate unilateral C5 spinal cord contusion on LysM-eGFP reporter mice to visualize infiltrating macrophages. At 6-weeks post-SCI, mice exhibit nociceptive and depressive-like dysfunction compared to naïve and sham groups. There were no differences between the sexes, indicating that sex is not a contributing factor driving nociceptive or depressive-like behaviors after SCI. Utilizing hierarchical cluster analysis, we classified mice based on endpoint nociceptive and depressive-like behavior scores. Approximately 59.3% of the SCI mice clustered based on increased paw withdrawal threshold to mechanical stimuli and immobility time in the forced swim test. SCI mice displayed increased myeloid cell presence in the lesion epicenter, ipsilateral C7-8 dorsal horn, and C7-8 DRGs as evidenced by eGFP, CD68, and Iba1 immunostaining when compared to naïve and sham mice. This was further confirmed by SCI-induced alterations in the expression of genes indicative of myeloid cell activation states and their associated secretome in the dorsal horn and dorsal root ganglia. In conclusion, moderate unilateral cervical SCI caused the development of pain-related and depressive-like behaviors in a subset of mice and these behavioral changes are consistent with immune system activation in the segmental pain pathway. PERSPECTIVE: These experiments characterized pain-related and depressive-like behaviors and correlated these changes with the immune response post-SCI. While humanizing the rodent is impossible, the results from this study inform clinical literature to closely examine sex differences reported in humans to better understand the underlying shared etiologies of pain and depressive-like behaviors following central nervous system trauma.

Mimicking opioid analgesia in cortical pain circuits

The anterior cingulate cortex plays a pivotal role in the cognitive and affective aspects of pain perception. Both endogenous and exogenous opioid signaling within the cingulate mitigate cortical nociception, reducing pain unpleasantness. However, the specific functional and molecular identities of cells mediating opioid analgesia in the cingulate remain elusive. Given the complexity of pain as a sensory and emotional experience, and the richness of ethological pain-related behaviors, we developed a standardized, deep-learning platform for deconstructing the behavior dynamics associated with the affective component of pain in mice-LUPE (Light aUtomated Pain Evaluator). LUPE removes human bias in behavior quantification and accelerated analysis from weeks to hours, which we leveraged to discover that morphine altered attentional and motivational pain behaviors akin to affective analgesia in humans. Through activity-dependent genetics and single-nuclei RNA sequencing, we identified specific ensembles of nociceptive cingulate neuron-types expressing mu-opioid receptors. Tuning receptor expression in these cells bidirectionally modulated morphine analgesia. Moreover, we employed a synthetic opioid receptor promoter-driven approach for cell-type specific optical and chemical genetic viral therapies to mimic morphine's pain-relieving effects in the cingulate, without reinforcement. This approach offers a novel strategy for precision pain management by targeting a key nociceptive cortical circuit with on-demand, non-addictive, and effective analgesia.

Chronic pain as an emergent property of a complex system and the potential roles of psychedelic therapies

Despite research advances and urgent calls by national and global health organizations, clinical outcomes for millions of people suffering with chronic pain remain poor. We suggest bringing the lens of complexity science to this problem, conceptualizing chronic pain as an emergent property of a complex biopsychosocial system. We frame pain-related physiology, neuroscience, developmental psychology, learning, and epigenetics as components and mini-systems that interact together and with changing socioenvironmental conditions, as an overarching complex system that gives rise to the emergent phenomenon of chronic pain. We postulate that the behavior of complex systems may help to explain persistence of chronic pain despite current treatments. From this perspective, chronic pain may benefit from therapies that can be both disruptive and adaptive at higher orders within the complex system. We explore psychedelic-assisted therapies and how these may overlap with and complement mindfulness-based approaches to this end. Both mindfulness and psychedelic therapies have been shown to have transdiagnostic value, due in part to disruptive effects on rigid cognitive, emotional, and behavioral patterns as well their ability to promote neuroplasticity. Psychedelic therapies may hold unique promise for the management of chronic pain.

Neuroscientific results of experimental studies on the control of acute pain with hypnosis and suggested analgesia

This narrative review summarizes a representative collection of electrophysiological and imaging studies on the neural processes and brain sources underlying hypnotic trance and the effects of hypnotic suggestions on the processing of experimentally induced painful events. It complements several reviews on the effect of hypnosis on brain processes and structures of chronic pain processing. Based on a summary of previous findings on the neuronal processing of experimentally applied pain stimuli and their effects on neuronal brain structures in healthy subjects, three neurophysiological methods are then presented that examine which of these neuronal processes and structures get demonstrably altered by hypnosis and can thus be interpreted as neuronal signatures of the effect of analgesic suggestions: (A) On a more global neuronal level, these are electrical processes of the brain that can be recorded from the cranial surface of the brain with magnetoencephalography (MEG) and electroencephalography (EEG). (B) On a second level, so-called evoked (EPs) or event-related potentials (ERPs) are discussed, which represent a subset of the brain electrical parameters of the EEG. (C) Thirdly, imaging procedures are summarized that focus on brain structures involved in the processing of pain states and belong to the main imaging procedures of magnetic resonance imaging (MRI/fMRI) and positron emission tomography (PET). Finally, these different approaches are summarized in a discussion, and some research and methodological suggestions are made as to how this research could be improved in the future.

Neuroinflammation drives sex-dependent effects on pain and negative affect in a murine model of repeated mild traumatic brain injury

ABSTRACT

The Center for Disease Control and Prevention estimates that 75% of reported cases of traumatic brain injury (TBI) are mild, where chronic pain and depression are 2 of the most common symptoms. In this study, we used a murine model of repeated mild TBI to characterize the associated pain hypersensitivity and affective-like behavior and to what extent microglial reactivity contributes to these behavioral phenotypes. Male and female C57BL/6J mice underwent sham or repeated mild traumatic brain injury (rmTBI) and were tested for up to 9 weeks postinjury, where an anti-inflammatory/neuroprotective drug (minocycline) was introduced at 5 weeks postinjury in the drinking water. Repeated mild traumatic brain injury mice developed cold nociceptive hypersensitivity and negative affective states, as well as increased locomotor activity and risk-taking behavior. Minocycline reversed negative affect and pain hypersensitivities in male but not female mice. Repeated mild traumatic brain injury also produced an increase in microglial and brain-derived neurotropic factor mRNA transcripts in limbic structures known to be involved in nociception and affect, but many of these changes were sex dependent. Finally, we show that the antiepileptic drug, gabapentin, produced negative reinforcement in male rmTBI mice that was prevented by minocycline treatment, whereas rmTBI female mice showed a place aversion to gabapentin. Collectively, pain hypersensitivity, increased tonic-aversive pain components, and negative affective states were evident in both male and female rmTBI mice, but suppression of microglial reactivity was only sufficient to reverse behavioral changes in male mice. Neuroinflammation in limbic structures seems to be a contributing factor in behavioral changes resulting from rmTBI.

Night time heart rate predicts next-day pain in fibromyalgia and primary back pain

Introduction

Primary chronic pain is pain that persists for over 3 months without associated measurable tissue damage. One of the most consistent findings in primary chronic pain is its association with autonomic hyperactivation. Yet whether the autonomic hyperactivation causes the pain or results from it is still unclear. It is also unclear to what extent autonomic hyperactivation is related to experienced pain intensity in different subtypes or primary chronic pain.

Objectives

Our first aim was to test lagged relationships between the markers of autonomic activation (heart rate) and pain intensity to determine its directionality. The main question here was whether autonomic biomarkers predict pain intensity or whether pain intensity predicts autonomic biomarkers. The second aim was to test whether this relationship is different between people with primary back pain and people with fibromyalgia.

Methods

Sixty-six patients with chronic pain were observed over an average of 81 days. Sleep heart rate and heart rate variability were measured with a wearable sensor, and pain intensity was assessed from daily subjective reports.

Results

The results showed a predictive relationship between sleep heart rate and next-day pain intensity (P < 0.05), but not between daily pain intensity and next night heart rate. There was no interaction with the type of chronic pain.

Conclusions

These findings suggest that autonomic hyperactivation, whether stress-driven or arising from other causes, precedes increases in primary chronic pain. Moreover, the present results suggest that autonomic hyperactivation is a common mechanism underlying the pain experience in fibromyalgia and chronic back pain.

Cingulate cortical thickness in cocaine use disorder: mediation effect between early life stress and cocaine consumption

OBJECTIVE

The cingulate gyrus is implicated in the neurobiology of addiction, such as chronic cocaine consumption. Early life stress (ELS) is an important moderator of cocaine use disorder (CUD). Therefore, we investigated the effect of CUD on cingulate cortical thickness and tested whether a history of ELS could influence the effects of CUD.

METHODS

Participants aged 18-50 years (78 with CUD due to crack cocaine consumption and 53 healthy controls) underwent magnetic resonance imaging and the cingulate thickness (rostral anterior, caudal anterior, posterior, and isthmus regions) was analysed. The clinical assessment comprised the Childhood Trauma Questionnaire (CTQ) and the Addiction Severity Index. Group comparisons adjusting by sex, age, and education were performed. Mediation models were generated where lifetime cocaine use, CTQ score, and cortical thickness corresponded to the independent variable, intermediary variable, and outcome, respectively.

RESULTS

Group comparisons revealed significant differences in six out of eight cingulate cortices, showing lower thickness in the CUD group. Furthermore, years of regular cocaine use was the variable most associated with cingulate thickness. Negative correlations were found between CTQ scores and the isthmus cingulate (right hemisphere), as well as with the rostral anterior cingulate (left hemisphere). In the mediation analysis, we observed a significant negative direct effect of lifetime cocaine use on the isthmus cingulate and an indirect effect of cocaine use mediated by CTQ score.

CONCLUSION

Our findings suggest that a history of ELS could aggravate the negative effects of chronic cocaine use on the cingulate gyrus, particularly in the right isthmus cingulate cortex.

Hypnosis in psychotherapy, psychosomatics and medicine. A brief overview

Aspects of hypnosis and its application in psychotherapy, psychosomatics and medicine are examined and contextualized in the 250-year history of hypnosis. Imagination as an essential element of hypnotic treatments appeared as early as 1784 as an argument rejecting the theory of animal magnetism of Franz Anton Mesmer. In somnambulism of German romanticism, another proto-form of hypnosis after 1800, concepts of the mind-body problem were dealt with, which still characterize the understanding of unconscious mental processes today. Hypnosis was at the beginning of psychoanalysis, but was not pursued further by Sigmund Freud from 1900 onwards. Nevertheless, there were some hypnoanalytical approaches in the 20th century, as well as attempts to integrate hypnosis into behavior therapy. Techniques of imagination and relaxation combine both; in particular findings from cognitive psychology explain processes of both hypnosis and cognitive behavioral therapy. The influence of social psychology brought a new perspective to the debate about the nature of hypnosis, which continues to this day: is hypnosis to be understood as a special state of consciousness or is it a completely normal, mundane interaction? The experiments that were carried out to support one side or the other were also dependent on the hypnotizability of the subjects involved, as the more difficult hypnotic phenomena such as paralysis, hallucinations or identity delusions can only be demonstrated by highly hypnotizable subjects. The fact that these are not mere compliance reactions has now been proven by many studies using imaging techniques. But even those who are moderately hypnotizable benefit from hypnosis rituals. Variables postulated by socio-cognitive hypnosis researchers, such as motivation and expectation, are relevant, as is a good "hypnotic rapport." Practical application of hypnotherapy today is characterized by the innovative techniques and strategies developed by Milton H. Erickson. Research into the effectiveness of hypnosis in the field of psychotherapy and psychosomatics still leaves much to be done. The situation is different in the field of medical hypnosis, where there are considerably more studies with a satisfactory design and verifiable effects. However, the impact in practical application in everyday medical practice is still low. Newer developments such as virtual reality and artificial intelligence are being looked at with critical interest.

Development and characterization of a Gucy2d-cre mouse to selectively manipulate a subset of inhibitory spinal dorsal horn interneurons

Recent transcriptomic studies identified Gucy2d (encoding guanylate cyclase D) as a highly enriched gene within inhibitory dynorphin interneurons in the mouse spinal dorsal horn. To facilitate investigations into the role of the Gucy2d+ population in somatosensation, Gucy2d-cre transgenic mice were created to permit chemogenetic or optogenetic manipulation of this subset of spinal neurons. Gucy2d-cre mice created via CRISPR/Cas9 genomic knock-in were bred to mice expressing a cre-dependent reporter (either tdTomato or Sun1.GFP fusion protein), and the resulting offspring were characterized. Surprisingly, a much wider population of spinal neurons was labeled by cre-dependent reporter expression than previous mRNA-based studies would suggest. Although the cre-dependent reporter expression faithfully labeled ~75% of cells expressing Gucy2d mRNA in the adult dorsal horn, it also labeled a substantial number of additional inhibitory neurons in which no Gucy2d or Pdyn mRNA was detected. Moreover, cre-dependent reporter was also expressed in various regions of the brain, including the spinal trigeminal nucleus, cerebellum, thalamus, somatosensory cortex, and anterior cingulate cortex. Injection of AAV-CAG-FLEX-tdTomato viral vector into adult Gucy2d-cre mice produced a similar pattern of cre-dependent reporter expression in the spinal cord and brain, which excludes the possibility that the unexpected reporter-labeling of cells in the deep dorsal horn and brain was due to transient Gucy2d expression during early stages of development. Collectively, these results suggest that Gucy2d is expressed in a wider population of cells than previously thought, albeit at levels low enough to avoid detection with commonly used mRNA-based assays. Therefore, it is unlikely that these Gucy2d-cre mice will permit selective manipulation of inhibitory signaling mediated by spinal dynorphin interneurons, but this novel cre driver line may nevertheless be useful to target a broader population of inhibitory spinal dorsal horn neurons.

The moderating effect of resting heart rate variability on the relationship between pain catastrophizing and depressed mood: an empirical study

Previous research indicated that pain catastrophizing-a negative emotional and cognitive response toward actual or anticipated pain-could contribute to pain intensity and could be associated with depressive symptoms not just in chronic pain patients but in healthy population as well. Accumulated evidence suggests that resting heart rate variability (HRV) as a putative proxy of emotion regulation could moderate the association of self-reported pain catastrophizing and depressed mood. In the present cross-sectional study, we investigated these associations in a healthy young adult sample controlling for the effect of trait rumination. Seventy-two participants (58 females, mean age = 22.2 ± 1.79 years ranging from 19 to 28 years old) completed the Pain Catastrophizing Scale, the Zung Self-Rating Depression Scale and the Ruminative Response Scale. Resting HRV was measured by time domain metric of HRV, the root mean square of successive differences (RMSSD). The results showed that the relationship between pain catastrophizing and depressive symptoms is significantly moderated by resting HRV (indexed by lnRMSSD). Specifically, in participants with higher resting HRV there was no significant relationship between the two investigated variables, while in participants with relatively low or medium HRV pain catastrophizing and depressed mood showed significant positive association. The relationship remained significant after controlling for sex, age and trait rumination. These results might indicate that measuring pain catastrophizing and depressive symptoms is warranted in non-clinical samples as well and higher resting HRV could have a buffer or protective role against depressive symptoms.

Effectiveness and reliability of hypnosis in stereotaxy: a randomized study

BACKGROUND

Patients suffering from Parkinson's disease (PD) may experience pain during stereotactic frame (SF) fixation in deep brain stimulation (DBS). We assessed the role of hypnosis during the SF fixation in PD patients undergoing awake bilateral subthalamic nucleus (STN) DBS.

METHODS

N = 19 patients were included (N = 13 males, mean age 63 years; N = 10 allocated to the hypnosis and N = 9 allocated to the control groups). Patients were randomly assigned to the interventional (hypnosis and local anesthesia) or non-interventional (local anesthesia only) groups. The primary outcome was the pain perceived (the visual analogue scale (VAS)). Secondary outcomes were stress, anxiety, and depression, as measured by the perceived stress scale (PSS) and hospital anxiety and depression scale (HADS). Procedural distress was measured using the peritraumatic distress inventory (PDI-13).

RESULTS

In the hypnosis group, VASmean was 5.6 ± 2.1, versus 6.4 ± 1.2 in the control group (p = 0.31). Intervention and control groups reported similar VASmax scores (7.6 ± 2.1 versus 8.6 ± 1.6 (p = 0.28), respectively). Both groups had similar HADS scores (6.2 ± 4.3 versus 6.7 ± 1.92, p = 0.72 (HADSa) and 6.7 ± 4.2 versus 7.7 ± 3, p = 0.58 (HADSd)), so were the PSS scores (26.1 ± 6.3 versus 25.1 ± 7, p = 0.75). Evolutions of VASmean (R2 = 0.93, 95% CI [0.2245, 1.825], p = 0.03) and PDI-13 scores (R2 = 0.94, 95% CI [1.006, 6.279], p = 0.02) significantly differ over follow-up with patients in the hypnosis groups showing lower scores.

CONCLUSION

In this unblinded, randomized study, hypnosis does not influence pain, anxiety, and distress during awake SF fixation but modulates pain memory over time and may prevent the integration of awake painful procedures as a bad experience into the autobiographical memory of patients suffering from PD. A randomized controlled study with more data is necessary to confirm our findings.

Opposing Effects on Descending Control of Nociception by µ and κ Opioid Receptors in the Anterior Cingulate Cortex

BACKGROUND

The efficiency of descending pain modulation, commonly assessed with the conditioned pain modulation procedure, is diminished in patients with chronic pain. The authors hypothesized that the efficiency of pain modulation is controlled by cortical opioid circuits.

METHODS

This study evaluated the effects of µ opioid receptor activation in the anterior cingulate cortex on descending control of nociception, a preclinical correlate of conditioned pain modulation, in male Sprague-Dawley rats with spinal nerve ligation-induced chronic pain or in sham-operated controls. Additionally, the study explored the consequences of respective activation or inhibition of κ opioid receptor in the anterior cingulate cortex of naive rats or animals with neuropathic pain. Descending control of nociception was measured as the hind paw withdrawal response to noxious pressure (test stimulus) in the absence or presence of capsaicin injection in the forepaw (conditioning stimulus).

RESULTS

Descending control of nociception was diminished in the ipsilateral, but not contralateral, hind paw of rats with spinal nerve ligation. Bilateral administration of morphine in the anterior cingulate cortex had no effect in shams but restored diminished descending control of nociception without altering hypersensitivity in rats with neuropathic pain. Bilateral anterior cingulate cortex microinjection of κ opioid receptor antagonists, including nor-binaltorphimine and navacaprant, also re-established descending control of nociception in rats with neuropathic pain without altering hypersensitivity and with no effect in shams. Conversely, bilateral injection of a κ opioid receptor agonist, U69,593, in the anterior cingulate cortex of naive rats inhibited descending control of nociception without altering withdrawal thresholds.

CONCLUSIONS

Anterior cingulate cortex κ opioid receptor activation therefore diminishes descending control of nociception both in naive animals and as an adaptive response to chronic pain, likely by enhancing net descending facilitation. Descending control of nociception can be restored by activation of μ opioid receptors in the anterior cingulate cortex, but also by κ opioid receptor antagonists, providing a nonaddictive alternative to opioid analgesics. Navacaprant is now in advanced clinical trials.

EDITOR’S PERSPECTIVE