European Journal of Pain

Background. Lifetime exposure to trauma is associated with chronic pain. Separate studies of chronic pain and trauma report overlapping alterations in white matter microstructure, yet their distinct and cumulative effects remain unclear. Methods. White matter microstructure (fractional anisotropy [FA] and mean diffusivity [MD]) from the UK Biobank (N = 21,995) were analysed using linear mixed-effects models. First, group effects (chronic pain versus control) on white matter integrity within this cohort were established. To investigate distinct and cumulative impacts of trauma exposure at different developmental stages, main and interactive effects of group and trauma severity on FA and MD were examined in separate groups exposed to childhood maltreatment only, adulthood trauma only, and both. Sex-stratified analyses were conducted. Results. Chronic pain was associated with widespread alterations and was spatially refined to brainstem tracts and cingulum when accounting for maltreatment/trauma severity. Accounting for chronic pain, cumulative trauma severity was associated with alterations in brainstem, frontal and parietal tracts, whereas adulthood trauma showed comparable but attenuated patterns. Childhood maltreatment severity was associated with localised FA and MD reductions in brainstem tracts, sagittal stratum and superior longitudinal fasciculus. These effects were more pronounced in females than males. A chronic pain-by-maltreatment/trauma severity interaction was observed for FA in the superior cerebellar peduncle in females exposed to childhood maltreatment only. Conclusions. Distinct and interactive effects of chronic pain and maltreatment/trauma severity on white matter microstructure were evident. The findings suggest that trauma-informed care should be tailored by timing of exposure and sex in this population.

Low-intensity focused ultrasound (LIFU) is a non-invasive neuromodulation technique with a favorable safety profile in healthy volunteers. Participant-experienced symptoms however remain inconsistently measured, and prospective benchmarks are lacking. Here, we prospectively characterized symptoms associated with LIFU neuromodulation across eight studies using a standardized Report of Symptoms (ROS). We compiled 629 sessions (472 LIFU, 157 sham) in 106 healthy adults (28.1 +/- 9.8 years) across eight cortical and subcortical targets (500 kHz; extracranial ISPPA 3.9-33.3 W/cm2; mechanical index 0.5-1.4). The ROS rated 17 symptom domains from 0 (absent) to 3 (severe) before and after each session. New-onset incidence, symptom severity, and total symptom burden were compared between LIFU and sham. The same instrument was applied in 35 patients with chronic pain. Symptom profiles after LIFU were indistinguishable from sham across all 17 domains. Total symptom burden averaged approximately one domain per session and did not increase after LIFU (0.94 to 1.03; p = 0.120). Post-intervention burden was predicted by baseline burden (beta = 0.347, p < 0.001) but not by stimulation condition (p = 0.222). New-onset symptoms did not increase across up to 27 LIFU sessions (OR = 0.99, p = 0.73) and were weakly, non-significantly related to acoustic intensity (rho = 0.37). Across a prospective, sham-controlled dataset, LIFU added no measurable symptom burden and was well tolerated in healthy adults, with comparable tolerability in patients. These findings establish a benchmark for the safety of human LIFU neuromodulation and a foundation for its therapeutic translation.

Deficient descending pain inhibition assessed by conditioned pain modulation (CPM) is considered a common feature of various chronic pain disorders. Typically, CPM studies focus on one particular disorder making direct comparisons between disorders difficult. This cross-sectional study aimed to compare CPM effects between three clearly distinct chronic pain disorders and pain-free controls. Furthermore, patients were pooled with controls to explore whether subgroups showing different CPM effects could be separated independent of cohort membership. One hundred and forty participants (patients: 53 non-specific chronic low back pain [nsCLBP], 15 complex regional pain syndrome [CRPS], 14 neuropathic pain after spinal cord injury [painSCI]; 58 controls) were included. CPM effects were assessed in a remote, pain-free area using pressure pain thresholds as test stimulus and a cold water bath as conditioning stimulus. Cohort differences in CPM effects were analyzed using linear mixed models. The presence of subgroups showing different CPM effects was tested using latent class linear mixed models. CPM effects differed between cohorts (p = 0.011), driven mainly by reduced inhibitory CPM effects in patients with nsCLBP compared to patients with painSCI. Latent class analysis detected 3 subgroups with varying degrees of significant inhibitory CPM effects (ps [&le;] 0.002). All subgroups comprised patients and controls. These results oppose deficient descending pain inhibition as a common feature of chronic pain disorders. Additionally, the failure to identify subgroups without inhibitory CPM effects within a heterogenous patient/control sample challenges the utility of deficient CPM as predictor of chronic pain or treatment efficacy. PerspectiveInhibitory conditioned pain modulation, a measure of descending pain inhibition, is not consistently impaired across distinct chronic pain disorders. Furthermore, identifying individuals with impaired conditioned pain modulation within a heterogenous sample is difficult. Thus, for conditioned pain modulation to be clinically useful, its variability needs to be better understood.

Background. Pain influences motor function and has been proposed to reduce corticospinal and intracortical excitability. At the same time, performance can be maintained during pain, at the cost of increased perceived effort, a centrally generated signal reflecting resource engagement. Here, we tested whether contralateral thermal heat pain-related changes in corticospinal and intracortical excitability contribute to increased effort perception. Methods. In this preregistered transcranial magnetic stimulation (TMS) study, twenty-one healthy participants received single and paired pulse TMS at rest and during submaximal isometric right wrist flexions performed at 20% maximal peak force. Trials were conducted under a control condition or during contralateral thermal stimulation (painful or non-painful warm) applied to the left forearm. After each contraction, participants rated the intensity of their perceived effort. Corticospinal and intracortical excitability of the right wrist flexor was assessed at rest and during submaximal contractions. Results. Contralateral heat pain significantly increased perceived effort compared with the control and warm conditions. Contralateral heat pain did not reduce corticospinal or intracortical excitability. Conversely, contralateral heat pain increased corticospinal excitability, reflected primarily in decreased cortical silent period duration. Perceived effort was associated with the subjective experience of pain rather than with TMS-derived variables. Conclusions. These findings suggest that increased effort during contralateral heat pain cannot be attributed to inhibition of the primary motor cortex or the corticospinal pathway. The higher perceived effort in the presence of contralateral heat pain likely reflects the cognitive cost of pain rather than alterations in the transmission of the motor command.

Low back pain is a prevalent issue with few reliable treatments. Although there is great variation in clinical presentation within the low back pain population, little is known about the neurobiological mechanisms underlying these differences. In this study, we sought to stratify chronic low back pain patients (N = 275) into phenotypes characterized by correlated patterns of resting-state brain activity and sensory abnormalities (pain, numbness, and pins and needles) indicated on hand-drawn body maps. Our cross-decomposition analysis yielded phenotypes that resemble previously documented mechanistic pain types, revealing distinct brain connectivity patterns associated with different clinical presentations. Our model was then used to predict pain body maps from fMRI data in a small novel dataset of chronic pain subjects, suggesting that these relationships may generalize to other chronic pain conditions. Our results support the utility of resting-state fMRI in understanding the heterogeneity of chronic pain, which may be leveraged to develop more targeted pain treatments.

Pain demands attention and can disrupt task-related goals. Attention allocation is a key cognitive process supporting motor learning and disruption of internal schemas associated with attentional control during motor learning can result in interference in improvements in performance. Movement-contingent pain is an important characteristic of persistent musculoskeletal pain. Despite this, research exploring pain interference with motor learning and attention has exclusively utilised tonic pain paradigms. Understanding the impacts of movement-contingent pain on motor learning and attention may provide important insights into the interaction between pain and motor learning. The aim of this study was to; 1) explore the robustness of a movement-contingent pain paradigm across an extended period of training, 2) explore the impact of movement-contingent pain on improvements in performance and attentional allocation during motor learning. Three groups (healthy non-pain, healthy experimental-pain and persistent pain experimental-pain) completed ten trials of a motor sequence learning task while experiencing a movement-contingent electrical stimulation. Three task performance measures and five gaze indices, previously associated with attentional control, were collected. Results showed that; 1) low frequency electro-cutaneous stimulation could produce a valid and consistent pain experience across a sustained period of training, 2) attentional allocation becomes more efficient across learning, accompanied by improvements in task performance, 3) changes in task performance and attentional measures across training were similar in all groups despite the presence of pain, 4) movement-contingent experimental pain enhanced spatial performance at all time points in healthy participants but was not accompanied by a different pattern of attentional allocation. This study demonstrates that the impact of movement-contingent pain on motor learning is comparable to the impacts of tonic experimental pain and provides interesting insights into patterns of attentional allocation across time but little evidence that these attentional allocations are impacted by the presence of pain or a past history of pain.

Background: Chronic pain is associated with impaired muscle health, but whether these changes reflect site-specific factors, broader systemic factors, or both remains unclear. The purpose of this study is to determine whether normative markers of muscle health derived from MRI show site-specific patterns in chronic pain. Methods: UK Biobank participants who underwent whole-body MRI from 2006 to 2010 were included in this retrospective cross-sectional study. The MuscleMap Toolbox quantified volume and intramuscular fat (IMF) in 42 muscles of the abdomen, pelvis, and thigh. Normative models trained on a no pain group generated muscle-specific deviations from normal (i.e., Z-scores) for single- and multi-site chronic and acute pain. Results: Of 17,843 participants, the primary site-specific analysis included 9,704 no pain, 885 single-site chronic back pain (CBP), 438 single-site chronic hip pain (CHP), and 1,315 single-site chronic knee pain (CKP) participants (n=12,342; mean age 63.7{+/-}7.5 years; 52.7% female). Additional analyses included single-site chronic neck/shoulder pain, acute pain, and multi-site chronic pain groups. In CBP, deviations were localized to abdominal muscles, with decreased volume in 6/8 and increased IMF in 6/8. In CHP, deviations were broad, with decreased volume in 3/8 of the abdominal and 14/26 of the thigh muscles, and increased IMF in 6/8 of the abdominal, 5/8 of the pelvic, and 4/26 of the thigh muscles. In CKP, deviations were localized to thigh muscles, with decreased volume in 8/26 and increased IMF in 6/26. Acute pain groups showed no significant differences except for decreased volume in one thigh muscle in acute knee pain. With each additional chronic pain site, volume decreased ({beta}=-.078;IQR:-0.100-0.051), and IMF increased ({beta}=.085;IQR:0.066-0.101). Combined Z-scores classified chronic pain groups better than chance (accuracy: 48.6%;p<.001), but not acute pain groups (accuracy: 39.0%;p=.20). Conclusions: Whole-body MRI combined with AI-driven muscle segmentation and normative modeling revealed site-specific patterns of muscle health in single-site chronic pain.

Nociceptive pain is the most common pain condition, and moderate-to-severe nociceptive pain substantially impacts daily functioning, constituting a significant public health burden. Despite this, most studies investigating the neural mechanisms underlying somatosensory processing and inhibition have focused on other pain conditions (e.g., neuropathic, nociplastic, or mixed pain). Thus, the extent to which neural aberrancies detected in these other populations extend to or differentiate from nociceptive pain conditions remains largely unknown. In this study, 29 individuals with moderate-to-severe nociceptive pain (MSNP) and 47 pain-free (PF) controls underwent magnetoencephalography (MEG) alongside a paired-pulse somatosensory stimulation paradigm to examine somatosensory cortical processing and functional inhibition. Pain status and intensity were determined using validated pain questionnaires, painDETECT and PROMIS-29, respectively. MEG oscillatory responses were source localized via a beamformer to the primary somatosensory cortex (S1) and time series data were extracted from the peak voxel to quantify the dynamics of somatosensory gating (SG; index of cortical inhibitory processing), oscillatory response power, and spontaneous power. We found that adults with MSNP exhibit aberrant theta SG in contralateral S1 compared to PF controls, reflecting reduced functional inhibition of innocuous stimulus processing in this region. Additionally, individuals with MSNP demonstrated exaggerated gamma responses but blunted alpha responses in contralateral S1 to innocuous stimulation. Finally, individuals with MSNP were characterized by weaker spontaneous alpha in contralateral S1 that scaled with self-reported pain intensity. Together, these findings suggest that experiencing MSNP is associated with disrupted somatosensory and cortical inhibitory processing.

Introduction: Pain catastrophizing and pain self-efficacy are well-established predictors of health outcomes in chronic pain. Higher pain catastrophizing, a maladaptive cognitive process, predicts worse health outcomes, whereas higher pain self-efficacy, an adaptive cognitive process, predicts better health outcomes. This study examined whether pain catastrophizing and pain self-efficacy interactions predict physical and psychosocial health outcomes at 3 months and their change over 3-months among patients with chronic pain who sought care at a tertiary pain clinic. Methods: Adults with chronic pain (N = 181; 66.7% female; Mage = 58.7) completed baseline assessments of the Pain Catastrophizing Scale (PCS), Chronic Pain Self-Efficacy Scale (CPSS), and PROMIS measures of physical (pain intensity, pain interference, physical function) and psychosocial health (depression, anxiety, anger, loneliness). PROMIS measures were repeated at 3 months. Hierarchical multiple regression analyses tested PCS, CPSS, and their interaction as predictors of outcomes at 3 months and change scores from baseline to 3 months. Results: The PCS by CPSS interaction significantly improved prediction for physical function (Change in R2 = 0.02, p = .02). Higher baseline self-efficacy predicted better physical function (Beta = 0.65, p < .001), but this effect weakened with higher levels of pain catastrophizing. The interaction also predicted change scores in physical function (p = .025) but was marginal after false discovery rate correction (p = .059). Additionally, a significant interaction emerged for loneliness change scores (p = .01): higher self-efficacy predicted greater reductions in loneliness, attenuated by higher catastrophizing. Conclusion: Pain self-efficacy interacted with pain catastrophizing to predict physical function and loneliness at 3 months. Greater self-efficacy was associated with better outcomes, with associations diminished with higher levels of pain catastrophizing. Findings highlight the moderating role of adaptive and maladaptive cognitions and suggest interventions should address both processes to optimize recovery in physical and social functioning.

The anterior cingulate cortex (ACC) is a key brain center involved in cognitive and emotional processing that is implicated in a variety of neuropsychiatric disorders including chronic pain and depression. Circuit-targeted diagnosis and treatment of these disorders will require the capacity to precisely modulate ACC subregions. Toward that end, we recently developed and validated a novel low-intensity transcranial focused ultrasound device that can noninvasively and directly modulate ACC subdivisions in humans with millimeter precision. Here we describe the subjective reports of 36 individuals diagnosed with either chronic pain or major depression who received repeated brief stimulation trials (807 active, 797 sham; duration 30s-3min) spanning the dorsoventral extent of the ACC. Sonication immediately altered cognitive-emotional states (odds ratio 5.6, active versus sham), eliciting a positive-valence experience more often than negative (29% versus 8%) in both diagnostic groups. Sham-adjusted response rate varied across ACC targets, with the largest effects (Cohen's d ~ 0.8) observed in pregenual and subgenual ACC in subjects with chronic pain and depression, respectively. These rapid trial-by-trial responses to ACC stimulation predicted subsequent improvements in pain and depression severity at 24 hours. Collectively, these findings reveal that transcranial ultrasound can robustly evoke immediate, target-specific, clinically meaningful changes in cognitive-emotional state, demonstrating the potential of ultrasonic neuromodulation as a tool for individualized probing of circuit function and dysfunction.

Introduction: Acute low back pain is a leading cause of disability worldwide. Clinical guidelines recommend non-pharmacological therapies as first-line treatment and advise caution with opioid prescribing. However pharmacological therapies, including opioids and gabapentinoids, remain commonly used. The comparative risks of subsequent opioid use disorder (OUD) and overdose diagnosis associated with initial treatment modality in large, real-world populations is not well characterized. We estimated the incidence of new-onset OUD and overdose diagnosis among opioid-naive, Medicaid-insured adults with newly diagnosed acute low back pain and estimated the association between initial treatment modalities and subsequent OUD and overdose diagnosis risk. Methods: We conducted a retrospective cohort study using Medicaid T-MSIS Analytic files from 25 states (2016-2019). We identified opioid-naive adults with a new diagnosis of acute low back pain who initiated pharmacologic or non-pharmacologic treatment within 1 month of diagnosis. The primary outcome was incident OUD and overdose diagnosis (based on diagnosis codes in claims) during follow-up. Associations between initial treatment modality and OUD and overdose diagnosis risk were estimated using a non-parametric, doubly robust estimator to adjust for measured confounding. Results: The cohort included 525,002 opioid-naive adults initiating treatment for low back pain. The cumulative incidence of OUD and overdose diagnosis was 1.5% and 2.4% at 7 and 13 months, respectively. Compared to non-use, use of gabapentinoids during the first month of treatment was associated with the highest relative risk (increasing risk) by 130.1%, 95% confidence interval (CI): 117.8%, 142.3%), the second-highest relative risk was estimated for higher-dose opioids, defined as > 50 daily Morphine Milligram Equivalents (MME) (118.1%, 95% CI: 99.2%, 137.0%). Lower-dose, short-duration opioids ([&le;] 50 MME, [&le;] 7 days) were also associated with elevated risk, though substantially smaller in magnitude (20.8%, 95% CI: 13.8%, 27.9%). In contrast, non-pharmacologic, non-interventional therapies were associated with reduced OUD and overdose diagnosis risk, with physical therapy demonstrating the largest relative reduction of 34.0% (95% CI: -40.9%, -27.1%). Discussion: In opioid-naive Medicaid patients with acute low back pain, initial non-pharmacologic treatment was associated with reduced OUD and overdose diagnosis risk. Gabapentinoids and opioids were each associated with increased risk; for opioids, the degree of risk increased with higher doses and durations. These results support guideline recommendations favoring non-pharmacologic treatment as first-line therapy and indicate the importance of cautious prescribing when pharmacologic treatment is considered.

Pain captures attention and interferes with executive and motor processes but task performance may be preserved at the cost of more effort. In a preregistered fMRI study, 40 participants performed a visuomotor force-matching task at two force levels under individually calibrated painful or non-painful thermal stimulation, while reporting the intensity of perceived effort. Maintaining task performance under pain was associated with increased perceived effort and recruited brain regions involved in pain modulation and cognitive control. Region-of-interest analysis showed perceived effort was consistently linked to decreased anterior midcingulate cortex activity, whereas supplementary motor area contributions varied depending on its role in motor execution or pain processing. Across experimental condition, motor, pain-modulatory and cognitive-control regions were associated with effort perception. Independently of condition, effort perception was modulated by ventromedial prefrontal cortex and ventral striatum. These findings indicate that effort perception reflects brain activity within areas involved in motor, executive and valuation processes.

Background: Transcranial temporal interference stimulation (tTIS) is an emerging noninvasive neuromodulation approach that enables focal, frequency-specific modulation of deep brain regions, offering a novel method for investigating therapeutic mechanisms underlying brain and mental health disorders. Pain is a key target because it is a feature of multiple disorders and is increasingly understood to depend on brain circuits. Here, we tested the effects of tTIS on bilateral evoked pain, capitalizing on converging evidence from human and animal studies indicating that the primary motor cortex (M1) contains body-wide inter-effector regions and has descending projections to regions implicated in nociceptive, motivational, and autonomic processing, making it a key cortical target for pain modulation. Methods: We conducted a pre-registered, triple-blind, randomized crossover study (N = 32, 160 study sessions), investigating frequency-dependent effects of tTIS applied to the left M1 on experimentally evoked thermal pain in healthy adults. We tested four stimulation frequencies (10 Hz, 20 Hz, 70 Hz, and sham) on separate days (>10,000 pain trials total). Noxious heat was applied to both the right and left forearms using individually calibrated temperatures both pre- and post-stimulation. Results: Active tTIS produced significant analgesia at all stimulation frequencies (10 Hz, 20 Hz, and 70 Hz) relative to sham (Cohens d = 0.46-0.82, all p < 0.05). 10 Hz produced the greatest reduction (d = 0.82), and both 10 Hz and 20 Hz produced more analgesia than 70 Hz (d = 0.44 and 0.38, respectively; p < 0.05). Stimulation-related sensations were equivalent across frequencies, and participants were blind to condition. Pain reductions remained stable over a [~]40-min post-stimulation period and were bilateral, consistent with stimulation of body-wide inter-effector regions. Conclusions: These results provide the first evidence that tTIS can reliably reduce experimental pain perception in humans in a frequency-dependent manner, providing a foundation for noninvasive pain modulation with tTIS.

Chronic pain presents a leading challenge in the world today for both clinicians and researchers. Because chronic pain is difficult to explain and treat, it is often managed with opioids despite providing limited relief and contributing to dependence and misuse. Persistent pain can be maintained by altered central nervous system processing even in the absence of distinct tissue damage or disease, which may limit the efficacy of conventional pharmacological therapies that target nociceptive signal transmission rather than maladaptive central nervous system dynamics often present in those with chronic pain. Although neuroimaging studies have identified this shift from nociceptive to emotional circuits during pain chronification, a quantitative framework linking these neural changes to longitudinal pain trajectories or recovery is lacking. We present a parsimonious firing-rate model that can account for the development of and recovery from chronic pain, which is based on the theoretical framework established by Wilson and Cowan. The model provides a quantitative explanation of how sensitization, anxiety, and fear maintain pain even after an injury has healed, and how calming stimulus downregulates these processes to facilitate recovery. A study applying the same principles as the model produced an average pain decrease of 3.5 on the Visual Analog Scale (VAS), with all subjects experiencing a reduction in pain. These results, coupled with our model and findings in prior studies, suggest that increasing calming stimulus can reduce pain without necessitating pharmacological or invasive, resource-intensive interventions.

Background: Chronic pain is a multidimensional condition that often persists despite conventional treatment and adversely affects multiple domains of daily life. Music listening has emerged as a promising non-pharmacological intervention, with accumulating evidence supporting its beneficial effects on pain and associated psychological outcomes. However, despite growing evidence of efficacy, the translation of music listening into routine clinical practice remains limited, partly because intervention reporting has received comparatively little attention. Objective: To evaluate the effectiveness of music listening interventions for chronic pain and systematically assess the methodological quality and completeness of intervention reporting to identify barriers to reproducibility and clinical implementation. Methods: Systematic searches were conducted in PubMed, Cochrane Library, CINAHL, and Web of Science through June 2025, with no date restrictions on publication. Randomized controlled trials involving adults with chronic pain receiving music listening interventions were included. Two independent reviewers screened studies, extracted data, and assessed risk of bias. Intervention reporting was evaluated using the TIDieR checklist, and a random-effects meta-analysis was performed for pain intensity outcomes. Results: Ten RCTs involving 538 participants were included. Music listening interventions varied substantially in delivery, duration, and music selection procedures, reflecting considerable heterogeneity in intervention design. Most studies reported significant improvements in pain and psychological outcomes. Meta-analysis of eight trials (10 effect estimates), demonstrated a moderate reduction in pain intensity (SMD = -0.53, 95% CI: -0.96 to -0.11, p = 0.014; I2 = 76.2%). Although intervention rationale and procedures were generally well described, reporting of intervention modifications, treatment fidelity, and adherence was frequently incomplete. These reporting deficiencies may compromise reproducibility and limit translation into clinical practice. Conclusions: Music listening appears to be a safe, accessible, and scalable non-pharmacological intervention for chronic pain management, with benefits extending beyond pain reduction to psychological wellbeing, quality of life, and functioning. However, incomplete reporting of key intervention components may limit reproducibility and hinder clinical implementation. Future trials should adopt standardized and transparent reporting standards to facilitate implementation into clinical practice.

Individual variability in pain perception raises fundamental questions about how biological and experiential factors shape pain processing. Cognitive-demanding motor training is a key driver of use-dependent brain plasticity and may contribute to differences in pain responses. Using musicians as a model of cognitive-motor expertise, we examined how such experience influences cortical dynamics and pain perception during experimentally induced prolonged musculoskeletal pain. Resting-state electroencephalography (EEG) was recorded in musicians and non-musicians before (Day 1) and during pain development (Days 3 and 8) following intramuscular nerve growth factor (NGF) administration. We parameterized periodic (alpha peak frequency, power, frontal asymmetry) and aperiodic (exponent, offset) components of the EEG signal to characterize intrinsic cortical activity. During pain development, non-musicians exhibited slowing of peak alpha frequency, a neural marker associated with ongoing pain. In contrast, musicians showed preserved alpha dynamics and greater left frontal asymmetry, reflecting resilient top-down pain regulation. Musicians also displayed higher aperiodic exponent across sessions, suggesting that musical training shapes the excitation-to-inhibition (E:I) balance potentially reflecting a shift toward greater inhibitory activity. Notably, across all participants, only aperiodic features improved the prediction of pain severity, with higher exponents and higher offsets associated with lower pain ratings. These findings demonstrate that cognitive-motor training shapes cortical dynamics during sustained pain, supporting more stable, resilient cortical responses to pain. Such training also contributes to inter-individual variability in pain processing. Moreover, this study identifies aperiodic EEG components as predictors of pain severity and resilience.

Spinal cord injury (SCI) results in dysfunction of both motor and sensory systems, which can be characterized by neuropathic pain, hypersensitivity, muscular spasticity and rigidity. Most SCIs result from incidents such as vehicle accidents or falls, resulting in polytraumatic SCI that includes peripheral injuries in addition to direct CNS damage. Recent findings suggest that spinal cord synaptic plasticity plays a crucial role in neuropathic pain pathophysiology, specifically in association with spinal sensitization and the consequent onset of AMPA-related maladaptive plasticity. Further findings have demonstrated that nociceptive peripheral stimulation in the acute phase of SCI results in maladaptive spinal synaptic plasticity by overdriving GluA2-lacking calcium-permeable AMPARs (CP-AMPARs). Here, we investigated the effect of a spared nerve injury (SNI) in conjunction with SCI to determine the effect of polytraumatic SCI on maladaptive plasticity in the spinal cord. Near-IR quantitative Western blot analysis demonstrated that SCI+SNI increases spinal GluA1 expression, but not GluA2. Patch-clamp confirmed that AMPAR currents in spinal motorneurons increase after SCI with SNI, and decrease after the administration of NASPM, a CP-AMPAR antagonist. Data-driven analysis using non-linear principal components analysis (NL-PCA) also demonstrated that SCI with SNI produces a multivariate signature of AMPAR plasticity that is observed in other forms of nociceptive peripheral input, indicating a general mechanism for maladaptive plasticity in spinal motor systems in response to polytraumatic SCI.

Previous brain decoding studies indicate that an individuals pain experience can be robustly predicted from distributed patterns of brain activity. Two brain decoders have notably been associated respectively with the nociceptive and cognitive aspects of pain experience, the Neurologic Pain Signature (NPS) and the Stimulus-Intensity Independent Pain Signature (SIIPS). Yet, we still do not know if these brain patterns are also causally related to pain experience. To evaluate this possibility, we used high-field (7-Tesla) fMRI to test whether humans can alter their pain experience by bidirectionally modulating their pain-related brain activity in decoded neurofeedback paradigm. In a double-blind design, participants were trained to up- and down-regulate the NPS or the SIIPS. Our results indicate that participants can achieve bidirectional control of both signatures. NPS expression reliably increased during pain stimulation and covaried with both stimulus intensity and subjective ratings. In contrast, SIIPS expression did not show consistent stimulus-locked effects in the primary analyses. Importantly, reduction in pain rating was specific for SIIPS-training, whereas NPS has failed to show any consistent behavioral effect. Based on these preliminary findings, we hereby preregister a follow-up study, with specified rationale, hypotheses, experimental design, and analysis protocols.

IntroductionCannabis is increasingly used for pain management, with many patients reporting relief from chronic pain that did not respond to conventional treatments. However, cannabis is also associated with unwanted side effects including psychomimetic effects and the potential of developing a cannabis use disorder. To circumvent the central nervous system effects, we investigated whether a peripherally restricted cannabinoid receptor (CB1) agonist, PrNMI [(4-{2-[-(1E)-1[(4-propylnaphthalen-1-yl)methylidene]-1H-inden-3yl]ethyl}morpholine] attenuated pain hypersensitivity associated with nerve injury and profiled its abuse potential. Materials and MethodsMice with chronic constriction injury (CCI) of the sciatic nerve developed hypersensitivity to mechanical stimulation. Paw withdrawal thresholds were assessed following administration of PrNMI (i.p. 0.3 mg/kg and 0.6 mg/kg) or vehicle in CCI and sham mice. The conditioned place preference model was used to measure drug-reward to 0.6 mg/kg i.p. PrNMI in CCI and sham-injury control animals. We further assessed abuse potential to determine if PrNMI (0.5 mg/kg) would reinstate drug-seeking behavior in mice trained to self-administer intravenous fentanyl (10 g/kg/infusion). ResultsPrNMI administration transiently increased paw withdrawal thresholds in mice with CCI-induced allodynia in a dose-dependent manner. PrNMI conditioning did not produce a conditioned place preference in mice with either CCI or sham injury. Mice who had learned to self-administer fentanyl and went through extinction training did not reinstate drug-seeking behavior when administered PrNMI. DiscussionThe systemic CB1 receptor agonist PrNMI demonstrated analgesic benefit in alleviating mechanical allodynia associated with chronic constriction injury of the sciatic nerve without increasing addiction related behaviors associated with the establishment of addiction.

Objective: To evaluate whether glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are associated with improvements in pain severity, disability, quality of life, and physical function in adults with obesity and chronic low back pain (cLBP), and to explore potential mechanisms. Design: Prospective, single-arm cohort study. Subjects: Thirty-five adults (median age 41 years; 86% women) with obesity (median BMI 39.9 kg/m2) and cLBP initiating GLP-1 RAs (tirzepatide, n=24; semaglutide, n=11). Methods: Participants completed questionnaires at baseline, 3, 6, 9, and 12 months. The primary outcome was Brief Pain Inventory-Short Form (BPI-SF) pain severity. Secondary outcomes included body mass index (BMI), BPI-SF pain interference, Numerical Rating Scale (NRS) back pain, Oswestry Disability Index (ODI), and Short Form-12 (SF-12). At baseline and 6 months, a subset (n=24) underwent quantitative sensory testing, physical performance testing, and blood draws for inflammatory biomarkers (C-reactive protein, TNF-, IL-6, IL-10), adipokines (leptin, adiponectin), and hemoglobin A1c. Results: Over 12 months, BMI decreased by 12.5% (median 39.9 to 34.9 kg/m2, 95% CI [-6.6, -4.2]). BPI-SF pain severity improved (median 4.8 to 2.0, 95% CI [-2.1, -0.8]), as did pain interference, ODI, NRS back pain, and SF-12 physical component scores. Hemoglobin A1c, leptin, and C-reactive protein decreased. Adiponectin increased and physical performance improved, but neither reached significance. Experimental pain sensitivity was unchanged. Conclusions: GLP-1 RAs were associated with clinically meaningful improvements in pain, disability, and quality of life. These findings suggest GLP-1 RAs may be a promising nonsurgical therapy for cLBP; randomized controlled trials are needed to establish causality and mechanisms.