Altered Primary Motor Cortex Structure, Organization, and Function in Chronic Pain: A Systematic Review and Meta-Analysis

Enhanced motor network engagement during reward gain anticipation in fibromyalgia

Reward motivation is essential in shaping human behavior and cognition. Both reward motivation and reward brain circuits are altered in chronic pain conditions, including fibromyalgia. In this study of fibromyalgia patients, we used a data-driven independent component analysis (ICA) approach to investigate how brain networks contribute to altered reward processing. From females with fibromyalgia (N = 24) and female healthy controls (N = 24), we acquired fMRI data while participants performed a monetary incentive delay (MID) reward task. After analyzing the task-based fMRI data using ICA to identify networks, we analyzed 3 networks of interest: motor network (left), value-driven attention network, and basal ganglia network. Then, we evaluated correlation coefficients between each network timecourse versus a task-based timecourse which modeled gain anticipation. Compared to controls, the fibromyalgia cohort demonstrated significantly stronger correlation between the left motor network timecourse and the gain anticipation timecourse, indicating the left motor network was more engaged with gain anticipation in fibromyalgia. In an exploratory analysis, we compared motor network engagement during early versus late phases of gain anticipation. Across cohorts, greater motor network engagement (i.e., stronger correlation between network and gain anticipation) occurred during the late timepoint, which reflected enhanced motor preparation immediately prior to response. Consistent with the main results, patients exhibited greater engagement of the motor network during both early and late phases compared with healthy controls. Visual-attention and basal ganglia networks revealed similar engagement in the task across groups. As indicated by post-hoc analyses, motor network engagement was positively related to anxiety and negatively related to reward responsiveness. In summary, we identified enhanced reward-task related engagement of the motor network in fibromyalgia using a novel data-driven ICA approach. Enhanced motor network engagement in fibromyalgia may relate to impaired reward motivation, heightened anxiety, and possibly to altered motor processing, such as restricted movement or dysregulated motor planning.

Tetraspanin profiles of serum extracellular vesicles reflect functional limitations and pain perception in knee osteoarthritis

BACKGROUND

Emerging evidence suggests that extracellular vesicles (EVs) can play roles in inflammatory processes and joint degradation in primary osteoarthritis (OA), a common age-associated joint disease. EV subpopulations express tetraspanins and platelet markers that may reflect OA pathogenesis. The present study investigated the associations between these EV surface markers and articular cartilage degradation, subjectively and objectively assessed pain, and functional limitations in primary knee OA (KOA).

METHODS

Serum EVs were determined by high-sensitivity flow cytometry (large CD61+ EVs) and single particle interferometric reflectance imaging sensor (small CD41+, CD63+, CD81+, and CD9+ EVs) from end-stage KOA patients and controls (n = 8 per group). Knee pain and physical functions were assessed with several health- and pain-related questionnaires, established measurements of physical medicine, and neuromuscular examination. The obtained data were analyzed using supervised and unsupervised univariate and multivariate models.

RESULTS

With the combined dataset of cartilage thickness, knee function, pain, sensation, and EV molecular signatures, we identified highly correlated groups of variables and found several EV markers that were statistically significant predictors of pain, physical limitations, and other aspects of well-being for KOA patients, for instance CD41+/CD63+/CD9+ small EVs associated with the range of motion of the knee, physical performance, and pain sensitivity.

CONCLUSIONS

Particular serum EV subpopulations showed clear associations with KOA pain and functional limitations, suggesting that their implications in OA pathophysiology warrant further study.

Pain-sensorimotor interactions: New perspectives and a new model

How pain and sensorimotor behavior interact has been the subject of research and debate for many decades. This article reviews theories bearing on pain-sensorimotor interactions and considers their strengths and limitations in the light of findings from experimental and clinical studies of pain-sensorimotor interactions in the spinal and craniofacial sensorimotor systems. A strength of recent theories is that they have incorporated concepts and features missing from earlier theories to account for the role of the sensory-discriminative, motivational-affective, and cognitive-evaluative dimensions of pain in pain-sensorimotor interactions. Findings acquired since the formulation of these recent theories indicate that additional features need to be considered to provide a more comprehensive conceptualization of pain-sensorimotor interactions. These features include biopsychosocial influences that range from biological factors such as genetics and epigenetics to psychological factors and social factors encompassing environmental and cultural influences. Also needing consideration is a mechanistic framework that includes other biological factors reflecting nociceptive processes and glioplastic and neuroplastic changes in sensorimotor and related brain and spinal cord circuits in acute or chronic pain conditions. The literature reviewed and the limitations of previous theories bearing on pain-sensorimotor interactions have led us to provide new perspectives on these interactions, and this has prompted our development of a new concept, the Theory of Pain-Sensorimotor Interactions (TOPSMI) that we suggest gives a more comprehensive framework to consider the interactions and their complexity. This theory states that pain is associated with plastic changes in the central nervous system (CNS) that lead to an activation pattern of motor units that contributes to the individual's adaptive sensorimotor behavior. This activation pattern takes account of the biological, psychological, and social influences on the musculoskeletal tissues involved in sensorimotor behavior and on the plastic changes and the experience of pain in that individual. The pattern is normally optimized in terms of biomechanical advantage and metabolic cost related to the features of the individual's musculoskeletal tissues and aims to minimize pain and any associated sensorimotor changes, and thereby maintain homeostasis. However, adverse biopsychosocial factors and their interactions may result in plastic CNS changes leading to less optimal, even maladaptive, sensorimotor changes producing motor unit activation patterns associated with the development of further pain. This more comprehensive theory points towards customized treatment strategies, in line with the management approaches to pain proposed in the biopsychosocial model of pain.

Brain stimulation targets for chronic pain: Insights from meta-analysis, functional connectivity and literature review

Noninvasive brain stimulation (NIBS) techniques have demonstrated their potential for chronic pain management, yet their efficacy exhibits variability across studies. Refining stimulation targets and exploring additional targets offer a possible solution to this challenge. This study aimed to identify potential brain surface targets for NIBS in treating chronic pain disorders by integrating literature review, neuroimaging meta-analysis, and functional connectivity analysis on 90 chronic low back pain patients. Our results showed that the primary motor cortex (M1) (C3/C4, 10-20 EEG system) and prefrontal cortex (F3/F4/Fz) were the most used brain stimulation targets for chronic pain treatment according to the literature review. The bilateral precentral gyrus (M1), supplementary motor area, Rolandic operculum, and temporoparietal junction, were all identified as common potential NIBS targets through both a meta-analysis sourced from Neurosynth and functional connectivity analysis. This study presents a comprehensive summary of the current literature and refines the existing NIBS targets through a combination of imaging meta-analysis and functional connectivity analysis for chronic pain conditions. The derived coordinates (with integration of the international electroencephalography (EEG) 10/20 electrode placement system) within the above brain regions may further facilitate the localization of these targets for NIBS application. Our findings may have the potential to expand NIBS target selection beyond current clinical trials and improve chronic pain treatment.

Females with painful temporomandibular disorders present higher intracortical facilitation relative to pain-free controls

OBJECTIVES

This study aimed to investigate cortical excitability differences in the primary motor cortex (M1) hand representation between individuals with temporomandibular disorders (TMD) and healthy controls. We assessed resting motor thresholds, motor-evoked potentials (MEPs), intracortical inhibition, and intracortical facilitation and explored potential associations with clinical and psychosocial characteristics in the TMD group.

MATERIALS AND METHODS

We recruited 36 female participants with TMD and 17 pain-free controls. Transcranial magnetic stimulation (TMS) was used to assess M1 cortical excitability. Correlations between clinical and psychosocial factors and cortical excitability measures were also evaluated.

RESULTS

Patients with TMD showed significantly higher intracortical facilitation at 12 ms (z = 1.98, p = 0.048) and 15 ms (z = 2.65, p = 0.008) when compared to controls. Correlations revealed associations between intracortical facilitation and pain interference, sleep quality, depressive symptoms, and pain catastrophizing in the TMD group.

CONCLUSIONS

Females with TMD exhibit heightened motor cortex intracortical facilitation in the hand representation, potentially indicating altered cortical excitability beyond the motor face area. This suggests a role for cortical excitability in TMD pathophysiology, influenced by psychosocial factors.

CLINICAL RELEVANCE

Understanding cortical excitability in TMD may inform targeted interventions. Psychosocial variables may play a role in cortical excitability, emphasizing the multidimensional nature of TMD-related pain. Further research is needed to confirm and expand upon these findings, with potential implications for the management of TMD and related pain conditions.

Combined transcranial magnetic stimulation and electroencephalography reveals alterations in cortical excitability during pain

Transcranial magnetic stimulation (TMS) has been used to examine inhibitory and facilitatory circuits during experimental pain and in chronic pain populations. However, current applications of TMS to pain have been restricted to measurements of motor evoked potentials (MEPs) from peripheral muscles. Here, TMS was combined with electroencephalography (EEG) to determine whether experimental pain could induce alterations in cortical inhibitory/facilitatory activity observed in TMS-evoked potentials (TEPs). In Experiment 1 (n=29), multiple sustained thermal stimuli were administered to the forearm, with the first, second, and third block of thermal stimuli consisting of warm but non-painful (pre-pain block), painful (pain block) and warm but non-painful (post-pain block) temperatures, respectively. During each stimulus, TMS pulses were delivered while EEG (64 channels) was simultaneously recorded. Verbal pain ratings were collected between TMS pulses. Relative to pre-pain warm stimuli, painful stimuli led to an increase in the amplitude of the frontocentral negative peak ~45 ms post-TMS (N45), with a larger increase associated with higher pain ratings. Experiments 2 and 3 (n=10 in each) showed that the increase in the N45 in response to pain was not due to changes in sensory potentials associated with TMS, or a result of stronger reafferent muscle feedback during pain. This is the first study to use combined TMS-EEG to examine alterations in cortical excitability in response to pain. These results suggest that the N45 TEP peak, which indexes GABAergic neurotransmission, is implicated in pain perception and is a potential marker of individual differences in pain sensitivity.

Altered effective connectivity from cerebellum to motor cortex in chronic low back pain: A multivariate pattern analysis and spectral dynamic causal modeling study

To explore the central processing mechanism of pain perception in chronic low back pain (cLBP) using multi-voxel pattern analysis (MVPA) based on the static and dynamic fractional amplitude of low-frequency fluctuations (fALFF) analysis, and spectral dynamic causal modeling (spDCM). Thirty-two patients with cLBP and 29 matched healthy controls (HCs) for the first cohort and 24 patients with cLBP and 22 HCs for the validation cohort underwent resting-state fMRI scan. The alterations in static and dynamic fALFF were as classification features to distinguish patients with cLBP from HCs. The brain regions gotten from the MVPA results were used for further spDCM analysis. We found that the most discriminative brain regions that contributed to the classification were the right supplementary motor area (SMA.R), left paracentral lobule (PCL.L), and bilateral cerebellar Crus II. The spDCM results displayed decreased excitatory influence from the bilateral cerebellar Crus II to PCL.L in patients with cLBP compared with HCs. Moreover, the conversion of effective connectivity from the bilateral cerebellar Crus II to SMA.R from excitatory influence to inhibitive influence, and the effective connectivity strength exhibited partially mediated effects on Chinese Short Form Oswestry Disability Index Questionnaire (C-SFODI) scores. Our findings suggest that the cerebellum and its weakened or inhibited connections to the motor cortex may be one of the underlying feedback pathways for pain perception in cLBP, and partially mediate the degree of dysfunction.

Pain-motor integration in chronic pain: A neurophysiological study

OBJECTIVE

Chronic pain may lead to functional changes in several brain regions, including the primary motor cortex (M1). Our neurophysiological study aimed to probe M1 plasticity, through a non-invasive transcranial magnetic stimulation protocol, in a cohort of patients with chronic pain.

METHODS

Twenty patients with chronic pain (age ± SD: 62.9 ± 9.9) and 20 age- and sex-matched healthy controls (age ± SD: 59.6 ± 15.8) were recruited. Standardized scales were used for the evaluation of pain severity. Neurophysiological measures included laser-evoked potentials (LEPs) and motor-evoked potentials (MEPs) collected at baseline and over 60 minutes following a standardized Laser-paired associative stimulation (Laser-PAS) protocol.

RESULTS

LEPs and MEPs were comparable in patients with chronic pain and controls. The pain threshold was lower in patients than in controls. Laser-PAS elicited decreased responses in patients with chronic pain. The response to Laser-PAS was similar in subgroups of patients with different chronic pain phenotypes.

CONCLUSIONS

M1 plasticity, as tested by Laser-PAS, is altered in patients with chronic pain, possibly reflecting abnormal pain-motor integration processes.

SIGNIFICANCE

Chronic pain is associated with a disorder of M1 plasticity raising from abnormal pain-motor integration.

Alterations in cortical excitability during pain: A combined TMS-EEG Study

Transcranial magnetic stimulation (TMS) has been used to examine inhibitory and facilitatory circuits during experimental pain and in chronic pain populations. However, current applications of TMS to pain have been restricted to measurements of motor evoked potentials (MEPs) from peripheral muscles. Here, TMS was combined with electroencephalography (EEG) to determine whether experimental pain could induce alterations in cortical inhibitory/facilitatory activity observed in TMS-evoked potentials (TEPs). In Experiment 1 (n = 29), multiple sustained thermal stimuli were administered to the forearm, with the first, second and third block of thermal stimuli consisting of warm but non-painful (pre-pain block), painful (pain block) and warm but non-painful (post-pain block) temperatures respectively. During each stimulus, TMS pulses were delivered while EEG (64 channels) was simultaneously recorded. Verbal pain ratings were collected between TMS pulses. Relative to pre-pain warm stimuli, painful stimuli led to an increase in the amplitude of the frontocentral negative peak ~45ms post-TMS (N45), with a larger increase associated with higher pain ratings. Experiments 2 and 3 (n = 10 in each) showed that the increase in the N45 in response to pain was not due to changes in sensory potentials associated with TMS, or a result of stronger reafferent muscle feedback during pain. This is the first study to use combined TMS-EEG to examine alterations in cortical excitability in response to pain. These results suggest that the N45 TEP peak, which indexes GABAergic neurotransmission, is implicated in pain perception and is a potential marker of individual differences in pain sensitivity.

Tampa Scale of Kinesiophobia may underestimate task-specific fear of movement in people with and without low back pain

Introduction

The Tampa Scale of Kinesiophobia (TSK) is commonly used to assess fear of movement (FoM) in people with low back pain (LBP). However, the TSK does not provide a task-specific measure of FoM, whereas image-based or video-based methods may do so.

Objectives

To compare the magnitude of FoM when assessed using 3 methods (TSK-11, image of lifting, video of lifting) in 3 groups of people: current LBP (LBP), recovered LBP (rLBP), and asymptomatic controls (control).

Methods

Fifty-one participants completed the TSK-11 and rated their FoM when viewing images and videos depicting people lifting objects. Low back pain and rLBP participants also completed the Oswestry Disability Index (ODI). Linear mixed models were used to estimate the effects of methods (TSK-11, image, video) and group (control, LBP, rLBP). Linear regression models were used to assess associations between the methods on ODI after adjusting for group. Finally, a linear mixed model was used to understand the effects of method (image, video) and load (light, heavy) on fear.

Results

In all groups, viewing images (P = 0.009) and videos (P = 0.038) elicited greater FoM than that captured by the TSK-11. Only the TSK-11 was significantly associated with the ODI (P < 0.001). Finally, there was a significant main effect of load on fear (P < 0.001).

Conclusion

Fear of specific movements (eg, lifting) may be better measured using task-specific measures, such as images and videos, than by task-generic questionnaires, such as the TSK-11. Being more strongly associated with the ODI, the TSK-11 still plays an important role in understanding the impact of FoM on disability.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

Group differences and associations between patient-reported outcomes and physical characteristics in chronic low back pain patients and healthy controls

BACKGROUND

Patients with chronic low back pain can exhibit altered slower gait, poor balance, and lower strength/power, and psychological dysfunctions such as pain catastrophizing and fear of movement. Few studies have investigated the relationships between physical and psychological dysfunctions. This study examined associations between patient-reported outcomes (pain interference, physical function, central sensitization, and kinesiophobia) and physical characteristics (gait, balance, and trunk sensorimotor characteristics).

METHODS

Laboratory testing included a 4-m walk, balance, and trunk sensorimotor testing with 18 patients and 15 controls. Gait and balance were collected with inertial measurement units. Isokinetic dynamometry measured trunk sensorimotor characteristics. Patient-reported outcomes included PROMIS Pain Interference / Physical Function, Central Sensitization Inventory, and Tampa Scale of Kinesiophobia. Independent t-tests or Mann-Whitney U tests were used to compare between groups. Additionally, Spearman's rank correlation coefficient (r_s) established associations between physical and psychological domains, and Fisher z-tests compared correlation coefficient values between groups (significance P < 0.05).

FINDINGS

The patient group had worse tandem balance and all patient-reported outcomes (P < 0.05) while no group differences were observed in gait and trunk sensorimotor characteristics. There were significant correlations between worse central sensitization and poor tandem balance (r_s = 0.446-0.619, P < 0.05) and lower peak force and rate of force development (r_s = -0.429-0.702, P < 0.05).

INTERPRETATION

Observed group differences in tandem balance agree with previous studies, indicating impaired proprioception. The current findings provide preliminary evidence that balance and trunk sensorimotor characteristics were significantly associated with patient-reported outcomes in patients. Early and period screening could help clinicians further categorize patients and develop objective treatment plans.

Altered Functional Networks during Gain Anticipation in Fibromyalgia

Reward motivation is essential in shaping human behavior and cognition. Previous studies have shown altered reward motivation and reward brain circuitry in chronic pain conditions, including fibromyalgia. Fibromyalgia is a chronic disorder characterized by widespread musculoskeletal pain, fatigue, cognitive problems, and mood-related symptoms. In this study, we analyzed brain reward networks in patients with fibromyalgia by using a data-driven approach with task-based fMRI data. fMRI data from 24 patients with fibromyalgia and 24 healthy controls were acquired while subjects performed a monetary incentive delay (MID) reward task. Functional networks were derived using independent component analysis (ICA) focused on the gain anticipation phase of the reward task. Functional activity in the motor, value-driven attention, and basal ganglia networks was evaluated during gain anticipation in both patient and healthy control groups. Compared to controls, the motor network was more engaged during gain anticipation in patients with fibromyalgia. Our findings suggest that reward motivation may lead to hyperactivity in the motor network, possibly related to altered motor processing, such as restricted movement or dysregulated motor planning in fibromyalgia. As an exploratory analysis, we compared levels of motor network engagement during early and late timepoints of the gain anticipation phase. Both groups showed greater motor network engagement during the late timepoint (i.e., closer to response), which reflected motor preparation prior to target response. Importantly, compared to controls and consistent with the initial findings described above, patients exhibited greater engagement of the motor network during both early and late timepoints. In summary, by using a novel data-driven ICA approach to analyze task-based fMRI data, we identified elevated motor network engagement during gain anticipation in fibromyalgia.

Tactile acuity and left/right judgment performance in patients with knee osteoarthritis: A cross-sectional study

BACKGROUND

Left/right judgment task (LRJT) performance and tactile acuity are impaired in chronic pain conditions, however, evidence is limited for knee osteoarthritis (OA).

OBJECTIVE

To compare LRJT performance and the two-point discrimination threshold (TPDT) of chronic knee OA patients with asymptomatic knee and pain-free controls.

DESIGN

Cross-sectional study.

METHODS

Fifty knee OA patients and 50 age and gender-matched pain-free controls were assessed using the Recognize® application by displaying knee images and a digital caliper for the TPDT of the medial and lateral knee joint line.

RESULTS

TPDTs over the lateral joint line in symptomatic (mean difference [MD]: 13.59 mm; 95% confidence interval [CI]: 8.72, 18.46; d = 1.40) and asymptomatic knee (MD: 10.15 mm; 95% CI: 5.08, 15.22; d = 0.99) were significantly increased compared to pain-free controls. Similarly, TPDTs of the medial joint line were significantly increased in symptomatic (MD: 12.19 mm; 95% CI: 7.59, 16.79; d = 1.31) and asymptomatic knee (MD: 7.64 mm; 95% CI: 3.64, 11.64; d = 1.31) compared to pain-free controls. Patients with knee OA were less accurate (MD: 7.80%; 95% CI: 15.32, -0.27; d = 0.52) recognizing images of their symptomatic knee. No correlation was found between pain severity, pain duration, LRJT performance, and TPDTs. Post-hoc analysis revealed no differences in LRJT and TPDTs between patients with and without clinically relevant symptoms of central sensitization.

CONCLUSION

Chronic knee OA is associated with increased TPDT for medial and lateral knee joint lines and decreased recognition accuracy performance which should be considered during treatment process.

Altered brain activities in mesocorticolimbic pathway in primary dysmenorrhea patients of long-term menstrual pain

Background

Patients with primary dysmenorrhea (PDM) often present with abnormalities other than dysmenorrhea including co-occurrence with other chronic pain conditions and central sensitization. Changes in brain activity in PDM have been demonstrated; however, the results are not consistent. Herein, this study probed into altered intraregional and interregional brain activity in patients with PDM and expounded more findings.

Methods

A total of 33 patients with PDM and 36 healthy controls (HCs) were recruited and underwent a resting-state functional magnetic resonance imaging scan. Regional homogeneity (ReHo) and mean amplitude of low-frequency fluctuation (mALFF) analysis were applied to compare the difference in intraregional brain activity between the two groups, and the regions with ReHo and mALFF group differences were used as seeds for functional connectivity (FC) analysis to explore the difference of interregional activity. Pearson's correlation analysis was conducted between rs-fMRI data and clinical symptoms in patients with PDM.

Results

Compared with HCs, patients with PDM showed altered intraregional activity in a series of brain regions, including the hippocampus, the temporal pole superior temporal gyrus, the nucleus accumbens, the pregenual anterior cingulate cortex, the cerebellum_8, the middle temporal gyrus, the inferior temporal gyrus, the rolandic operculum, the postcentral gyrus and the middle frontal gyrus (MFG), and altered interregional FC mainly between regions of the mesocorticolimbic pathway and regions associated with sensation and movement. The anxiety symptoms are correlated with the intraregional activity of the right temporal pole superior temporal gyrus and FC between MFG and superior frontal gyrus.

Conclusion

Our study showed a more comprehensive method to explore changes in brain activity in PDM. We found that the mesocorticolimbic pathway might play a key role in the chronic transformation of pain in PDM. We, therefore, speculate that the modulation of the mesocorticolimbic pathway may be a potential novel therapeutic mechanism for PDM.

Lower corticospinal excitability and greater fatigue among people with multiple sclerosis experiencing pain

Introduction

Persons with multiple sclerosis (MS) frequently report pain that negatively affects their quality of life. Evidence linking pain and corticospinal excitability in MS is sparse. We aimed to (1) examine differences in corticospinal excitability in MS participants with and without pain and (2) explore predictors of pain.

Methods

Sixty-four participants rated their pain severity on a visual analog scale (VAS). Transcranial magnetic stimulation (TMS) and validated clinical instruments characterized corticospinal excitability and subjective disease features like mood and fatigue. We retrieved information on participants' prescriptions and disability status from their clinical records.

Results

Fifty-five percent of participants reported pain that affected their daily functioning. Persons with pain had significantly greater fatigue and lower area under the excitatory motor evoked potential (MEP) recruitment curve (eREC AUC), a measure of total corticospinal excitability. After controlling for age, disability status, and pain medications, increased fatigue and decreased eREC AUC together explained 40% of the variance in pain.

Discussion

Pain in MS is multifactorial and relates to both greater fatigue and lesser corticospinal excitability. Future work should better characterize relationships between these outcomes to develop targeted pain interventions such as neuromodulation.

Summary

We examined pain in MS. Individuals with pain had higher fatigue and lower corticospinal excitability than those without pain. These outcomes significantly predicted self-reported pain.

FDG PET Imaging of the Pain Matrix in Neuropathic Pain Model Rats

Pain is an unpleasant subjective experience that is usually modified by complex multidimensional neuropsychological processes. Increasing numbers of neuroimaging studies in humans have characterized the hierarchical brain areas forming a pain matrix, which is involved in the different dimensions of pain components. Although mechanistic investigations have been performed extensively in rodents, the homologous brain regions involved in the multidimensional pain components have not been fully understood in the rodent brain. Herein, we successfully identified several brain regions activated in response to mechanical allodynia in neuropathic pain rat models using an alternative neuroimaging method based on 2-deoxy-2-[¹⁸F]fluoro-d-glucose positron emission tomography (FDG PET) scanning. Regions such as the medial prefrontal cortex, primary somatosensory cortex hindlimb region, and the centrolateral thalamic nucleus were identified. Moreover, brain activity in these regions was positively correlated with mechanical allodynia-related behavioral changes. These results suggest that FDG PET imaging in neuropathic pain model rats enables the evaluation of regional brain activity encoding the multidimensional pain aspect. It could thus be a fascinating tool to bridge the gap between preclinical and clinical investigations.

Transcranial magnetic stimulation maps the neurophysiology of chronic noncancer pain: A scoping review

BACKGROUND

Chronic noncancer pain is a global public health challenge. It is imperative to identify biological markers ("biomarkers") to understand the mechanisms underlying chronic pain and to monitor pain over time and after interventions. Transcranial magnetic stimulation (TMS) is a promising method for this purpose.

OBJECTIVES

To examine differences in TMS-based outcomes between persons with chronic pain and healthy controls (HCs) and/or before versus after pain-modulating interventions and relationships between pain measures and TMS outcomes; To summarize the neurophysiological mechanisms underlying chronic pain as identified by TMS.

METHODS

We searched the PubMed database for literature from January 1, 1985, to June 9, 2020, with the keywords "pain" and "transcranial magnetic stimulation." Eligible items included original studies of adult human participants with pain lasting for ≥ 6 months. We completed a narrative synthesis of the study findings stratified by chronic pain etiology (primary pain, neuropathic pain, and secondary musculoskeletal pain).

RESULTS

The search yielded 1265 records. The final 12 articles included 244 patients with chronic pain (192 females, aged 35-65 years) and 169 HCs (89 females, aged 28-59 years). Abnormalities in TMS outcomes that reflect GABAergic and glutamatergic activities were associated with many of the disorders studied and were distinct for each pain etiology. Chronic primary pain is characterized by reduced intracortical inhibition and corticospinal excitability, chronic neuropathic pain shows evidence of increased excitation and disinhibition, and chronic secondary musculoskeletal pain involves low corticospinal excitability.

DISCUSSION

TMS could be a useful tool for delineating the neurophysiological underpinnings of chronic pain syndromes.

Functional connectivity response to acute pain assessed by fNIRS is associated with BDNF genotype in fibromyalgia: an exploratory study

Fibromyalgia is a heterogenous primary pain syndrome whose severity has been associated with descending pain modulatory system (DPMS) function and functional connectivity (FC) between pain processing areas. The brain-derived neurotrophic factor (BDNF) Val66Met single nucleotide polymorphism has been linked to vulnerability to chronic pain. In this cross-sectional imaging genetics study, we investigated fibromyalgia, the relationship between BDNF Val66Met heterozygous genotypes (Val/Met), and the functional connectivity (FC) response pattern to acute pain stimulus in the motor (MC) and prefrontal (PFC) cortex assessed by near-infrared spectroscopy (fNIRS) before and after a cold pressor test utilizing water (0-1 °C). Also, we assessed the relationship between this genotype with the DPMS function and quality of life. We included 42 women (Val/Val = 30; Val/Met = 12) with fibromyalgia, ages 18-65. The MANCOVA comparing Val/Met to Val/Val genotypes showed higher ΔFC between left(l)-PFC-l-MC (β = 0.357, p = 0.048), l-PFC-right(r)-PFC (β = 0.249, p = 0.012), l-PFC-r-MC (β = 0.226, p = 0.022), and l-MC-r-PFC (β = 0.260, p = 0.016). Val/Met genotypes showed higher efficiency of the DPMS and lower disability due to pain. Here we show that fibromyalgia patients carrying the Val/Met BDNF genotype presented an increased ΔFC across MC and PFC in response to acute pain associated with differences in acute pain perception and fibromyalgia symptoms.

Functional Changes in Cortical Activity of Patients Submitted to Knee Osteoarthritis Treatment: An Exploratory Pilot Study

INTRODUCTION

There is evidence that brain plasticity is the central mechanism involved in the functional recovery process of patients with knee osteoarthritis. Studies involving the analysis of central nervous system mechanisms of pain control and recovery could provide more data on future therapeutic approaches.

OBJECTIVE

The aim of the study was to explore possible functional changes in cortical activity of patients submitted to knee osteoarthritis standardized pain treatment using electroencephalography.

METHODOLOGY

Ten patients with clinical and radiological diagnosis of painful knee unilateral or bilateral osteoarthritis were recruited to participate in clinical (Pain's Visual Analog Scale), radiological (Kellgren-Lawrence Scale), and neurophysiological (electroencephalography) assessments to evaluate cortical activity during cortical pain modulation activity. The clinical and neurophysiological analyses were performed before and after standardized pain treatment.

RESULTS

Eight patients participated in this study. A significant improvement in pain perception and relative increase in interhemispheric connectivity after therapies was observed. In electroencephalography analysis, tests with real movement showed a relative increase in density directed at Graph's analysis.

CONCLUSIONS

Relative increase density directed measures at connectivity analysis in electroencephalography after pain treatment can be possible parameters to be explored in future research with a larger number of patients.

The Effect of Acute and Sustained Pain on Corticomotor Excitability: A Systematic Review and Meta-Analysis of Group and Individual Level Data

Pain alters motor function. This is supported by studies showing reduced corticomotor excitability in response to experimental pain lasting &lt;90 minutes. Whether similar reductions in corticomotor excitability are present with pain of longer durations or whether alterations in corticomotor excitability are associated with pain severity is unknown. Here we evaluated the evidence for altered corticomotor excitability in response to experimental pain of differing durations in healthy individuals. Databases were systematically searched for eligible studies. Measures of corticomotor excitability and pain were extracted. Meta-analyses were performed to examine: (1) group-level effect of pain on corticomotor excitability, and (2) individual-level associations between corticomotor excitability and pain severity. 49 studies were included. Corticomotor excitability was reduced when pain lasted milliseconds-seconds (hedges g's = -1.26 to -1.55) and minutes-hours (g's = -0.55 to -0.9). When pain lasted minutes-hours, a greater reduction in corticomotor excitability was associated with lower pain severity (g = -0.24). For pain lasting days-weeks, there were no group level effects (g = -0.18 to 0.27). However, a greater reduction in corticomotor excitability was associated with higher pain severity (g = 0.229). In otherwise healthy individuals, suppression of corticomotor excitability may be a beneficial short-term strategy with long-term consequences. PERSPECTIVE: This systematic review synthesised the evidence for altered corticomotor excitability in response to experimentally induced pain. Reduced corticomotor excitability was associated with lower acute pain severity but higher sustained pain severity, suggesting suppression of corticomotor excitability may be a beneficial short-term adaptation with long-term consequences.

The relationship between handgrip and rotator cuff muscle strength in shoulder pain: a cross-sectional study

Background/Aims

Shoulder pain is reported to be the third most common musculoskeletal disorder. Rotator cuff muscles play an important role in stabilising the shoulder and decreasing pain. Assessment of handgrip strength has been proposed as an indicator of rotator cuff function in healthy individuals, but not in those experiencing shoulder pain. The aim of this study was to assess the relationship between handgrip strength and shoulder rotator cuff strength in patients experiencing shoulder pain as a result of pathology or surgical intervention. A secondary aim was to identify any association between the duration of shoulder pain and handgrip strength and shoulder rotator cuff strength.

Methods

A total of 32 patients with shoulder pain (19 men, 13 women) were evaluated. The mean age was 52.88 (± 15.66) years, with a mean duration of shoulder pain of 13.44 (± 10.22) weeks. Handgrip strength was measured using the standard Jamar hydraulic hand dynamometer, and individual isometric rotator cuff strength was measured using the Baseline push-pull dynamometer.

Results

Correlation was found between handgrip strength and the abductor (r=0.58), external rotator (r=0.57), and internal rotator strength (r=0.59). A linear regression model was used to derive the equations for the association. No significant (P>0.05) correlation was found between the duration of pain and the handgrip strength or rotator cuff strength.

Conclusions

The strength of the correlation found indicates that handgrip strength can be used for assessment and within a rehabilitation programme to monitor rotator cuff function in patients with shoulder pain or post-surgical rehabilitation. The strength of rotator cuff muscles can be predicted by the equations derived from the regression model relating to grip strength assessment.

Altered Brain Activity and Effective Connectivity within the Nonsensory Cortex during Stimulation of a Latent Myofascial Trigger Point

Myofascial trigger point (MTrP), an iconic characteristic of myofascial pain syndrome (MPS), can induce cerebral cortex changes including altered cortical excitability and connectivity. The corresponding characteristically reactive cortex is still ambiguous. Seventeen participants with latent MTrPs underwent functional near-infrared spectroscopy (fNIRS) to collect cerebral oxygenation hemoglobin (Δ[oxy-Hb]) signals. The Δ[oxy-Hb] signals of the left/right prefrontal cortex (L/R PFC), left/right motor cortex (L/R MC), and left/right occipital lobe (L/R OL) of the subjects were measured using functional near-infrared spectroscopy (fNIRS) in the resting state, nonmyofascial trigger point (NMTrP), state and MTrP state. The data investigated the latent MTrP-induced changes in brain activity and effective connectivity (EC) within the nonsensory cortex. The parameter wavelet amplitude (WA) was used to describe cortical activation, EC to show brain network connectivity, and main coupling direction (mCD) to exhibit the dominant connectivity direction in different frequency bands. An increasing trend of WA and a decreasing trend of EC values were observed in the PFC. The interregional mCD was primarily shifted from a unidirectional to bidirectional connection, especially from PFC to MC or OL, when responding to manual stimulation during the MTrP state compared with resting state and NMTrP state in the intervals III, IV, and V. This study demonstrates that the nonsensory cortex PFC, MC, and OL can participate in the cortical reactions induced by stimulation of a latent MTrP. Additionally, the PFC shows nonnegligible higher activation and weakened regulation than other brain regions. Thus, the PFC may be responsible for the central cortical regulation of a latent MTrP. This trial is registered with ChiCTR2100048433.

Sex and gender differences in pain

Chronic pain affects 20% of adults and is one of the leading causes of disability worldwide. Women and girls are disproportionally affected by chronic pain. About half of chronic pain conditions are more common in women, with only 20% having a higher prevalence in men. There are also sex and gender differences in acute pain sensitivity. Pain is a subjective experience made up of sensory, cognitive, and emotional components. Consequently, there are multiple dimensions through which sex and gender can influence the pain experience. Historically, most preclinical pain research was conducted exclusively in male animals. However, recent studies that included females have revealed significant sex differences in the physiological mechanisms underlying pain, including sex specific involvement of different genes and proteins as well as distinct interactions between hormones and the immune system that influence the transmission of pain signals. Human neuroimaging has revealed sex and gender differences in the neural circuitry associated with pain, including sex specific brain alterations in chronic pain conditions. Clinical pain research suggests that gender can affect how an individual contextualizes and copes with pain. Gender may also influence the susceptibility to develop chronic pain. Sex and gender biases can impact how pain is perceived and treated clinically. Furthermore, the efficacy and side effects associated with different pain treatments can vary according to sex and gender. Therefore, preclinical and clinical research must include sex and gender analyses to understand basic mechanisms of pain and its relief, and to develop personalized pain treatment.

A Dysfunctional Descending Pain Modulation System in Chronic Nonspecific Low Back Pain: A Systematic Review and ALE Meta-Analysis

Pain, a physiological protective mechanism, turns into a complex dynamic neural response when it becomes chronic. The role of neuroplastic brain changes is more evident than the peripheral factors in the maintenance, modulation and amplification of chronic low back pain (cLBP). In this background, we summarise the brain changes in cLBP in a coordinate-based activation likelihood estimation (ALE) meta-analysis of previous functional magnetic resonance imaging (fMRI) studies. Databases ('PubMed', 'Scopus' and 'Sleuth') were searched till May 2022 and the activity pattern was noted under the 'without stimulation' and 'with stimulation' groups. A total of 312 studies were selected after removing duplicates. Seventeen (553 cLBP patients, 192 activation foci) studies were fulfilled the eligibility criteria and included in the 'without stimulation' group. Twelve statistically significant clusters are localized in the prefrontal cortex, primary somatosensory cortex, primary motor cortex, parietal cortex, anterior cingulate cortex, caudate, putamen, globus pallidus amygdala, occipital lobe, temporal lobe and associated white matter in this group. Ten studies (353 cLBP patients, 125 activation foci) were selected in the' with stimulation' groups. In this group, seven statistically significant clusters were found in the frontal cortex, orbitofrontal cortex, premotor cortex, parietal cortex, claustrum and insula. These statistically significant clusters indicate a probable imbalance in GABAergic modulation of brain circuits and dysfunction in the descending pain modulation system. This disparity in the pain neuro-matrix is the source of spontaneous and persisting pain in cLBP.

Changes in the Brain Metabolism Associated with Central Post-Stroke Pain in Hemorrhagic Pontine Stroke: An 18F-FDG-PET Study of the Brain

Central post-stroke pain (CPSP) is an intractable neuropathic pain that can occur following central nervous system injuries. Spino-thalamo-cortical pathway damage contributes to CPSP development. However, brain regions involved in CPSP are unknown and previous studies were limited to supratentorial strokes with cortical lesion involvement. We analyzed the brain metabolism changes associated with CPSP following pontine hemorrhage. Thirty-two patients with isolated pontine hemorrhage were examined; 14 had CPSP, while 18 did not. Brain glucose metabolism was evaluated using 18F-fluorodeoxyglucose-positron emission tomography images. Additionally, regions revealing metabolic correlation with CPSP severity were analyzed. Patients with CPSP showed changes in the brain metabolism in the cerebral cortices and cerebellum. Compared with the control group, the CPSP group showed significant hypometabolism in the contralesional rostral anterior cingulum and ipsilesional primary motor cortex (Puncorrected < 0.001). However, increased brain metabolism was observed in the ipsilesional cerebellum (VI) and contralesional cerebellum (lobule VIIB) (Puncorrected < 0.001). Moreover, increased pain intensity correlated with decreased metabolism in the ipsilesional supplementary motor area and contralesional angular gyrus. This study emphasizes the role of the many different areas of the cortex that are involved in affective and cognitive processing in the development of CPSP.

The sensorimotor theory of pathological pain revisited

Harris (1999) proposed that pain can arise in the absence of tissue damage because changes in the cortical representation of the painful body part lead to incongruences between motor intention and sensory feedback. This idea, subsequently termed the sensorimotor theory of pain, has formed the basis for novel treatments for pathological pain. Here we review the evidence that people with pathological pain have changes to processes contributing to sensorimotor function: motor function, sensory feedback, cognitive representations of the body and its surrounding space, multisensory processing, and sensorimotor integration. Changes to sensorimotor processing are most evident in the form of motor deficits, sensory changes, and body representations distortions, and for Complex Regional Pain Syndrome (CRPS), fibromyalgia, and low back pain. Many sensorimotor changes are related to cortical processing, pain, and other clinical characteristics. However, there is very limited evidence that changes in sensorimotor processing actually lead to pain. We therefore propose that the theory is more appropriate for understanding why pain persists rather than how it arises.

Hyper-connectivity between the left motor cortex and prefrontal cortex is associated with the severity of dysfunction of the descending pain modulatory system in fibromyalgia

Introduction

The association between descending pain modulatory system (DPMS) dysfunction and fibromyalgia has been previously described, but more studies are required on its relationship with aberrant functional connectivity (FC) between the motor and prefrontal cortices.

Objectives

The objective of this cross-sectional observational study was to compare the intra- and interhemispheric FC between the bilateral motor and prefrontal cortices in women with fibromyalgia, comparing responders and nonresponders to the conditioned pain modulation (CPM) test.

Methods

A cross-sectional sample of 37 women (23 responders and 14 nonresponders to the CPM test) with fibromyalgia diagnosed according to the American College of Rheumatology criteria underwent a standardized clinical assessment and an FC analysis using functional near-infrared spectroscopy. DPMS function was inferred through responses to the CPM test, which were induced by hand immersion in cold water (0–1°C). A multivariate analysis of covariance for main effects between responders and nonresponders was conducted using the diagnosis of multiple psychiatric disorders and the use of opioid and nonopioid analgesics as covariates. In addition, we analyzed the interaction between the CPM test response and the presence of multiple psychiatric diagnoses.

Results

Nonresponders showed increased FC between the left motor cortex (lMC) and the left prefrontal cortex (lPFC) (t = −2.476, p = 0.01) and right prefrontal cortex (rPFC) (t = −2.363, p = 0.02), even when both were considered as covariates in the regression analysis (lMC–lPFC: β = −0.127, t = −2.425, p = 0.021; lMC–rPFC: β = −0.122, t = −2.222, p = 0.033). Regarding main effects, a significant difference was only observed for lMC–lPFC (p = 0.035). A significant interaction was observed between the psychiatric disorders and nonresponse to the CPM test in lMC−lPFC (β = −0.222, t = −2.275, p = 0.03) and lMC−rPFC (β = −0.211, t = −2.2, p = 0.035). Additionally, a significant interaction was observed between the CPM test and FC in these two region-of-interest combinations, despite the psychiatric diagnoses (lMC−lPFC: β = −0.516, t = −2.447, p = 0.02; lMC−rPFC: β = −0.582, t = −2.805, p = 0.008).

Conclusions

Higher FC between the lMC and the bilateral PFC may be a neural marker of DPMS dysfunction in women with fibromyalgia, although its interplay with psychiatric diagnoses also seems to influence this association.

Cervical musculoskeletal impairments in the 4 phases of the migraine cycle in episodic migraine patients

OBJECTIVE

To assess cervical musculoskeletal impairments during the 4 phases of a migraine cycle in episodic migraine patients, controlling for the presence of concomitant neck pain.

METHODS

Differences in cervical musculoskeletal impairments were assessed during the 4 migraine phases in episodic migraine patients and compared with healthy controls controlling for concomitant neck pain. Cervical musculoskeletal impairments were assessed as follow: cervical active range of motion; flexion rotation test; craniocervical flexion test and calculation of activation pressure score; the total number of myofascial trigger points in head/neck muscles; the number of positivevertebral segments (headache's reproduction) during passive accessory intervertebral movement; pressure pain thresholds over C1, C2, C4, C6 vertebral segments bilaterally, trigeminal area, hand, and leg. Signs of pain sensitization were assessed by evaluating mechanical pain threshold over trigeminal area and hand, pressure pain thresholds, and the wind-up ratio. The Bonferroni-corrected p-value (05/4 = 0.013) was adopted to assess the difference between groups, while a p-value of 0.05 was considered significant for the correlation analysis.

RESULTS

A total of 159 patients and 52 controls were included. Flexion rotation test and craniocervical flexion test were reduced in all 4 phases of the migraine cycle versus healthy controls (p < 0.001). The number of myofascial trigger points and positive vertebral segments was increased in all 4 phases of the migraine cycle versus healthy controls (p < 0.001). Flexion, extension, and total cervical active range of motion and cervical pressure pain thresholds were reduced in episodic migraine in the ictal phase versus controls (p < 0.007) with no other significant differences. Outside the ictal phase, the total cervical active range of motion was positively correlated with trigeminal and leg pressure pain threshold (p < 0.026), the number of active myofascial trigger points and positive positive vertebral segments were positively correlated with higher headache frequency (p=0.045), longer headache duration (p < 0.008), and with headache-related disability (p = 0.031). Cervical pressure pain thresholds were positively correlated with trigeminal, hand, and leg pressure pain threshold (p < 0.001), and trigeminal and leg mechanical pain thresholds (p < 0.005), and negatively correlated with the wind-up ratio (p < 0.004).

CONCLUSION

In all phases of the migraine cycle, independent of the presence of concomitant neck pain, episodic migraine patients showed reduced flexion rotation test and craniocervical flexion test and an increased number of myofascial trigger points and passive accessory vertebral segments. These impairments are correlated with enhanced headache duration, headache-related disability, and signs of widespread pain sensitization. Reduction in active cervical movement and increased mechanical hyperalgesia of the cervical was consistent in ictal episodic migraine patients and the subgroups of episodic migraine patients with more pronounced widespread sensitization.

Maladaptive motor cortical excitability and connectivity in polyneuropathy with neuropathic pain

BACKGROUND

Sensory symptoms, especially neuropathic pain, are common in polyneuropathy. Conventional diagnostic tools can evaluate structural or functional impairment of nerves but cannot reveal mechanisms of neuropathic pain. Changes in the brain after polyneuropathy may play roles in the genesis of neuropathic pain.

METHODS

This cross-sectional study investigated changes of cortical excitability within left primary motor cortex (M1) by measuring resting motor thresholds, short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and afferent inhibition between polyneuropathy patients and controls, and investigated the correlates of these parameters with neuropathic pain and the M1 structural and functional connectivity assessed by diffusion tractography imaging and functional MRI.

RESULTS

Thirty-three painful and 15 non-painful neuropathic patients and 21 controls were enrolled. There were no differences in intraepidermal nerve fiber density, nerve conduction study, thermal thresholds, or autonomic functional tests between patients with and without neuropathic pain. Compared to controls, neuropathic patients exhibited similar resting motor thresholds or afferent inhibition, but attenuated SICI and augmented ICF, especially in painful patients. Changes of intracortical excitability in neuropathic patients were correlated with intensities of neuropathic pain, and different presentations of SICI and ICF were noted between patients with and without thermal paresthesia. Additionally, short latency afferent inhibition at interstimulus intervals of 20 ms was associated with structural connectivity of left M1 with brain areas associated with pain perception.

CONCLUSIONS

Maladaptive cortical excitability with altered structural connectivity in left M1 developed after peripheral nerve degeneration and was associated with neuropathic pain and sensory symptoms in polyneuropathy.

Motor cortex excitability in chronic low back pain

Chronic pain is associated with dysfunctional cortical excitability. Research has identified altered intracortical motor cortex excitability in Chronic Lower Back Pain (CLBP). However, research identifying the specific intracortical changes underlying CLBP has been met with inconsistent findings. In the present case-control study, we examined intracortical excitability of the primary motor cortex using transcranial magnetic stimulation (TMS) in individuals with CLBP. Twenty participants with CLBP (M_age = 54.45 years, SD_age = 15.89 years) and 18 age- and gender-matched, pain-free controls (M = 53.83, SD = 16.72) were included in this study. TMS was applied to the hand motor area of the right hemisphere and motor evoked potentials (MEPs) were recorded from the first dorsal interosseous muscle of the contralateral hand. Resting motor threshold (rMT) and MEP amplitude were measured using single-pulse stimulation. Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed using paired-pulse stimulation. Individuals with CLBP had significantly higher rMT (decreased corticospinal excitability) and lower ICF compared to controls. No significant differences were found in MEP amplitude and SICI. These findings add to the growing body of evidence that CLBP is associated with deficits in intracortical modulation involving glutamatergic mechanisms.

Increased motor cortex inhibition as a marker of compensation to chronic pain in knee osteoarthritis

This study aims to investigate the associative and multivariate relationship between different sociodemographic and clinical variables with cortical excitability as indexed by transcranial magnetic stimulation (TMS) markers in subjects with chronic pain caused by knee osteoarthritis (OA). This was a cross-sectional study. Sociodemographic and clinical data were extracted from 107 knee OA subjects. To identify associated factors, we performed independent univariate and multivariate regression models per TMS markers: motor threshold (MT), motor evoked potential (MEP), short intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP). In our multivariate models, the two markers of intracortical inhibition, SICI and CSP, had a similar signature. SICI was associated with age (β: 0.01), WOMAC pain (β: 0.023), OA severity (as indexed by Kellgren–Lawrence Classification) (β: − 0.07), and anxiety (β: − 0.015). Similarly, CSP was associated with age (β: − 0.929), OA severity (β: 6.755), and cognition (as indexed by the Montreal Cognitive Assessment) (β: − 2.106). ICF and MT showed distinct signatures from SICI and CSP. ICF was associated with pain measured through the Visual Analogue Scale (β: − 0.094) and WOMAC (β: 0.062), and anxiety (β: − 0.039). Likewise, MT was associated with WOMAC (β: 1.029) and VAS (β: − 2.003) pain scales, anxiety (β: − 0.813), and age (β: − 0.306). These associations showed the fundamental role of intracortical inhibition as a marker of adaptation to chronic pain. Subjects with higher intracortical inhibition (likely subjects with more compensation) are younger, have greater cartilage degeneration (as seen by radiographic severity), and have less pain in WOMAC scale. While it does seem that ICF and MT may indicate a more acute marker of adaptation, such as that higher ICF and MT in the motor cortex is associated with lesser pain and anxiety.

Neurophysiological and psychophysical effects of dry versus sham needling of the infraspinatus muscle in patients with chronic shoulder pain: a randomized feasibility study

BACKGROUND

Dry needling (DN) is increasingly used for treating myofascial trigger points (MTrPs) and has shown significant effects on pain and function. This study aimed to assess feasibility of conducting a randomized sham-controlled trial and to collect preliminary data on the effects of infraspinatus DN on corticospinal excitability and mechanical pain sensitivity.

METHOD

This randomized feasibility study included adults with chronic non-traumatic shoulder pain and a infraspinatus MTrP. Participants were randomized to receive real DN or sham DN in the infraspinatus MTrP. Feasibility outcomes included data pertaining to recruitment, retention of participants, completeness and safety of assessment procedures. Neurophysiological and psychophysical outcomes included corticospinal excitability and mechanical pain sensitivity measured by active motor threshold (aMT) and pressure pain threshold (PPT), respectively. They were assessed at baseline, immediately after and 24 h post-intervention.

RESULTS

Twenty-one participants were recruited over a 6-month period. Nineteen participants completed the treatment and follow-up assessment. Motor evoked potential responses were discernible in all but 1 participant. Only 1 minor adverse event related to transcranial magnetic stimulation (mild headache) affected the measurements. No DN adverse effects were recorded in both groups. An overall completeness rate of 81% was reached, with 70% completeness in the DN group and 91% in the sham group. Data analysis revealed that real DN increased corticospinal excitability (reduced aMT) 24 h post-intervention (Mdn = - 5.96% MSO, IQR = 5.17, p = 0.04) and that sham DN triggered similar responses immediately after the intervention (Mdn = - 1.93% MSO, IQR = 1.11, p = 0.03). Increased mechanical pain sensitivity (reduced PPT) was significant only in the sham group, both immediately (Mdn = - 0.44 kg/cm2, IQR = 0.49, p = 0.01) and 24 h post-intervention (Mdn = - 0.52 kg/cm2, IQR = 1.02, p = 0.02). Changes in corticospinal excitability was positively correlated with changes in mechanical pain sensitivity in the DN group, both immediately (r = 0.77, p = 0.02) and 24 h post-intervention (r = 0.75, p = 0.05).

CONCLUSION

The present study demonstrates the feasibility of quantifying the neurophysiological and psychophysical effects of DN, and provides recommendations and guidelines for future studies. Moreover, it provides preliminary evidence that DN may increase corticospinal excitability of the infraspinatus muscle in patients with chronic shoulder pain and that the relationship of neurophysiological and psychophysical effects is promising to better understand its mechanisms of action.

TRIAL REGISTRATION

NCT04316793 ; retrospectively registered November 3, 2020.

Comparing the Impact of Multi-Session Left Dorsolateral Prefrontal and Primary Motor Cortex Neuronavigated Repetitive Transcranial Magnetic Stimulation (nrTMS) on Chronic Pain Patients

Repetitive transcranial stimulation (rTMS) has been shown to produce an analgesic effect and therefore has a potential for treating chronic refractory pain. However, previous studies used various stimulation parameters (including cortical targets), and the best stimulation protocol is not yet identified. The present study investigated the effects of multi-session 20 Hz (2000 pulses) and 5 Hz (1800 pulses) rTMS stimulation of left motor cortex (M1-group) and left dorsolateral prefrontal cortex (DLPFC-group), respectively. The M1-group (n = 9) and DLPFC-group (n = 7) completed 13 sessions of neuronavigated stimulation, while a Sham-group (n = 8) completed seven sessions of placebo stimulation. The outcome was measured using the German Pain Questionnaire (GPQ), Depression, Anxiety and Stress Scale (DASS), and SF-12 questionnaire. Pain perception significantly decreased in the DLPFC-group (38.17%) compared to the M1-group (56.11%) (p ≤ 0.001) on the later sessions. Health-related quality of life also improved in the DLPFC-group (40.47) compared to the Sham-group (35.06) (p = 0.016), and mental composite summary (p = 0.001) in the DLPFC-group (49.12) compared to M1-group (39.46). Stimulation of the left DLPFC resulted in pain relief, while M1 stimulation was not effective. Nonetheless, further studies are needed to identify optimal cortical target sites and stimulation parameters.

Experimental Hand and Knee Pain Cause Differential Effects on Corticomotor Excitability

Acute pain elicits a well-known inhibitory effect on upper limb corticomotor excitability, whereas the temporal effects of lower-limb experimental pain and pain in a remote limb are less clear. The aim of this study was to compare the temporal corticomotor excitability changes in the upper and lower limbs in response to acute upper and lower limb pain. In a cross-over design, 13 participants (age 29 ± 9 years; 12 male) attended 2 sessions where experimental pain was induced by injecting hypertonic saline into either the first dorsal interosseous (FDI) muscle or infrapatellar fat pad at the knee, inducing a short-lasting pain experience scored on a numerical rating scale (NRS). Motor evoked potentials (MEPs) in response to transcranial magnetic stimulation were recorded in the FDI and vastus lateralis (VL) muscles before, during, and following pain. Hand and knee pain NRS scores were not significantly different. Hand pain elicited a short duration inhibition of the FDI MEPs (P < .0001) together with a facilitation of VL MEPs (P = .001) that outlasted the duration of pain. Knee pain elicited a short-duration facilitation of VL MEPs (P = .003) with no significant effect in the FDI MEPs (P = .46). The findings indicate a limb-specific corticomotor response to experimental pain that may be related to limb function. PERSPECTIVE: These data demonstrate the impact of acute, experimental pain on corticomotor excitability in the upper and lower limbs. This facilitates our understanding of the effect of pain on motor control of both local and distant muscles.

The effect of experimental and clinical musculoskeletal pain on spinal and supraspinal projections to motoneurons and motor unit properties in humans: A systematic review

BACKGROUND AND OBJECTIVE

Numerous studies have examined the influence of pain on spinal reflex excitability, motor unit behaviour and corticospinal excitability. Nevertheless, there are inconsistencies in the conclusions made. This systematic review sought to understand the effect of pain on spinal and supraspinal projections to motoneurons and motor unit properties by examining the influence of clinical or experimental pain on the following three domains: H-reflex, corticospinal excitability and motor unit properties.

DATABASES AND DATA TREATMENT

MeSH terms and preselected keywords relating to the H-reflex, motor evoked potentials and motor unit decomposition in chronic and experimental pain were used to perform a systematic literature search using Cumulative Index of Nursing and Allied Health Literature (CINAHL), Excerpta Medica dataBASE (EMBASE), Web of Science, Medline, Google Scholar and Scopus databases. Two independent reviewers screened papers for inclusion and assessed the methodological quality using a modified Downs and Black risk of bias tool; a narrative synthesis and three meta-analyses were performed.

RESULTS

Sixty-one studies were included, and 17 different outcome variables were assessed across the three domains. Both experimental and clinical pain have no major influence on measures of the H-reflex, whereas experimental and clinical pain appeared to have differing effects on corticospinal excitability. Experimental pain consistently reduced motor unit discharge rate, a finding which was not consistent with data obtained from patients. The results indicate that when in tonic pain, induced via experimental pain models, inhibitory effects on motoneuron behaviour were evident. However, in chronic clinical pain populations, more varied responses were evident likely reflecting individual adaptations to chronic symptoms.

SIGNIFICANCE

This is a comprehensive systematic review and meta-analysis which synthesizes evidence on the influence of pain on spinal and supraspinal projections to motoneurons and motor unit properties considering measures of the H-reflex, corticospinal excitability and motor unit behaviour. The H-reflex is largely not influenced by the presence of either clinical or experimental pain. Whilst inhibitory effects on corticospinal excitability and motor unit behaviour were evident under experimental pain conditions, more variable responses were observed for people with painful musculoskeletal disorders.

The Relationship Between Corticomotor Reorganization and Acute Pain Severity: A Randomized, Controlled Study Using Rapid Transcranial Magnetic Stimulation Mapping

OBJECTIVE

Although acute pain has been shown to reduce corticomotor excitability, it remains unknown whether this response resolves over time or is related to symptom severity. Furthermore, acute pain research has relied upon data acquired from the cranial "hotspot," which do not provide valuable information regarding reorganization, such as changes to the distribution of a painful muscle's representation within M1. Using a novel, rapid transcranial magnetic stimulation (TMS) mapping method, this study aimed to 1) explore the temporal profile and variability of corticomotor reorganization in response to acute pain and 2) determine whether individual patterns of corticomotor reorganization are associated with differences in pain, sensitivity, and somatosensory organization.

METHODS

Corticomotor (TMS maps), pain processing (pain intensity, pressure pain thresholds), and somatosensory (two-point discrimination, two-point estimation) outcomes were taken at baseline, immediately after injection (hypertonic [n = 20] or isotonic saline [n = 20]), and at pain resolution. Follow-up measures were recorded every 15 minutes until 90 minutes after injection.

RESULTS

Corticomotor reorganization persisted at least 90 minutes after pain resolution. Corticomotor depression was associated with lower pain intensity than was corticomotor facilitation (r = 0.47 [P = 0.04]). These effects were not related to somatosensory reorganization or peripheral sensitization mechanisms.

CONCLUSIONS

Individual patterns of corticomotor reorganization during acute pain appear to be related to symptom severity, with early corticomotor depression possibly reflecting a protective response. These findings hold important implications for the management and potential prevention of pain chronicity. However, further research is required to determine whether these adaptations relate to long-term outcomes in clinical populations.

Nociceptive stress interferes with neural processing of cognitive stimuli in Gulf War Veterans with chronic musculoskeletal pain

AIMS

Disrupted cognition and chronic musculoskeletal pain (CMP) are prevalent experiences among Gulf War Veterans (GWV). A negative association between CMP and cognition (i.e., chronic pain-related cognitive interference) has been observed in some chronic pain populations but has not been evaluated in GWV. Additional research suggests that disrupted cognition in GWV with CMP may be exacerbated by stressing the nociceptive system. Therefore, we compared cognitive performance and related neural activity between CMP and healthy control (CO) GWV in the absence and presence of experimental pain.

MAIN METHODS

During functional magnetic resonance imaging (fMRI), Veterans (CMP = 29; CO = 27) completed cognitive testing via congruent and incongruent conditions of a modified Stroop task (Stroop-only). A random subset (CMP = 13; CO = 13) also completed cognitive testing with experimental pain (Pain+Stroop). Yuen's modified t-test and robust mixed-model analysis of variance (ANOVA) models were used for analyzing cognitive performance data. Independent t-tests and repeated-measures ANOVA models were employed for fMRI data with thresholding for multiple-comparisons (p < 0.005) and cluster size (> 320 mm³).

KEY FINDINGS

Functional MRI analysis revealed significant between-group differences for the incongruent but not congruent-Stroop run. Neither correct responses nor reaction time differed between groups in either Stroop condition (all p ≥ 0.21). Significant group (CMP, CO) by run (Stroop-only, Pain+Stroop) interactions revealed greater neural responses in CMP Veterans during Pain+Stroop runs. No significant interactions were observed for correct responses or reaction time (p ≥ 0.31).

SIGNIFICANCE

GWV with CMP require a greater amount of neural resources to sustain cognitive performance during nociceptive stress.

Enhanced amygdala-frontal operculum functional connectivity during rest in women with chronic neck pain: Associations with impaired conditioned pain modulation

BACKGROUND

Chronic neck pain is a leading cause of disability worldwide, affecting the lives of millions of people. Research investigating functional brain alterations in relation to somatosensory function is necessary to better understand mechanisms underlying pain development and maintenance in individuals with chronic neck pain, yet remains scarce. This case-control study aimed to examine resting-state functional connectivity alterations and associations with pain outcomes, self-reported central sensitization-related symptoms and quantitative sensory testing (QST) measures in patients with chronic non-traumatic (idiopathic/CINP) neck pain and chronic traumatic (whiplash associated/CWAD) neck pain compared to pain-free controls.

METHODS

Resting-state functional magnetic resonance images were acquired in 107 female participants (38 CINP, 37 CWAD, 32 healthy controls). After data pre-processing, seed-to-seed analyses were conducted focusing on resting-state functional connectivity involving pre-defined regions of interest that have previously been observed to be structurally or functionally altered and/or associated with pain-related measures in this patient population.

RESULTS

Findings demonstrate enhanced left amygdala functional coupling during rest with the left frontal operculum in women with CINP and CWAD compared to controls. This increased resting-state functional connectivity was associated with more self-reported symptoms related to central sensitization and decreased efficacy of conditioned pain modulation. Furthermore, enhanced connectivity between the left amygdala and left frontal orbital cortex, and between the left pallidum and the left frontal operculum was observed only in patients with CWAD compared to healthy controls. In patients, additional associations between local hyperalgesia and enhanced connectivity between the left superior parietal cortex and the left and right precentral gyrus were found.

CONCLUSIONS

In line with our hypotheses, patients with CWAD showed the most pronounced alterations in resting-state functional connectivity, encompassing subcortical limbic (amygdala) and basal ganglia (pallidum), and ventral frontal regions (frontal operculum, orbitofrontal cortex) when compared to CINP and controls. Findings are generally in line with the idea of a continuum, in absence of significant group differences across CINP and CWAD. Enhanced amygdala-frontal operculum functional connectivity was the most robust and only connectivity pair in the cluster that was associated with QST (i.e., dynamic QST; endogenous pain inhibition), and that was observed in both patient groups. In addition, independent of group differences, enhanced resting-state functional connectivity between superior parietal cortex (involved in attention) and primary motor cortex was associated with static QST (i.e., greater local hyperalgesia). Taken together, our findings show a key role for enhanced amygdala-ventral frontal circuitry in chronic neck pain, and its association with diminished endogenous pain inhibition further emphasizes the link between cognitive-affective and sensory modulations of pain in women with chronic non-traumatic and traumatic neck pain.

Correlating cognition and cortical excitability with pain in fibromyalgia: a case control study

BACKGROUND

Fibromyalgia is a chronic pain disorder characterized by widespread musculoskeletal symptoms, primarily attributed to sensitization of somatosensory system carrying pain. Few reports have investigated the impact of fibromyalgia symptoms on cognition, corticomotor excitability, sleepiness, and the sleep quality - all of which can deteriorate the quality of life in fibromyalgia. However, the existing reports are underpowered and have conflicting directions of findings, limiting their generalizability. Therefore, the present study was designed to compare measures of cognition, corticomotor excitability, sleepiness, and sleep quality using standardized instruments in the recruited patients of fibromyalgia with pain-free controls.

METHODS

Diagnosed cases of fibromyalgia were recruited from the Rheumatology department for the cross-sectional, case-control study. Cognition (Mini-Mental State Examination, Stroop color-word task), corticomotor excitability (Resting motor threshold, Motor evoked potential amplitude), daytime sleepiness (Epworth sleepiness scale), and sleep quality (Pittsburgh sleep quality index) were studied according to the standard procedure.

RESULTS

Thirty-four patients of fibromyalgia and 30 pain-free controls were recruited for the study. Patients of fibromyalgia showed decreased cognitive scores (p = 0.05), lowered accuracy in Stroop color-word task (for color: 0.02, for word: 0.01), and prolonged reaction time (< 0.01, < 0.01). Excessive daytime sleepiness in patients were found (< 0.01) and worsened sleep quality (< 0.01) were found. Parameters of corticomotor excitability were comparable between patients of fibromyalgia and pain-free controls.

CONCLUSIONS

Patients of fibromyalgia made more errors, had significantly increased reaction time for cognitive tasks, marked daytime sleepiness, and impaired quality of sleep. Future treatment strategies may include cognitive deficits and sleep disturbances as an integral part of fibromyalgia management.

Hyperalgesia and Central Sensitization in Subjects With Chronic Orofacial Pain: Analysis of Pain Thresholds and EEG Biomarkers

Introduction: The presence of a temporomandibular disorder is one of the most frequent causes of orofacial pain (OFP). When pain continues beyond tissue healing time, it becomes chronic and may be caused, among other factors, by the sensitization of higher-order neurons. The aim of this study is to describe psychological characteristics of patients with chronic OFP, their peripheral pain threshold, and electroencephalography (EEG) recording, looking for possible signs of central sensitization (CS). Materials and methods: Twenty-four subjects with chronic OFP caused by temporomandibular disorder were evaluated using the Research Diagnostic Criteria for Temporomandibular Disorders Axis I and Axis II. Pain intensity, catastrophizing, and presence of CS were assessed through self-reported questionnaires. Pressure pain threshold (PPT) was recorded in facial and peripheral sites; EEG activity was recorded during open and closed eyes resting state and also during the pain threshold assessment. Pain thresholds and EEG recordings were compared with a cohort of pain-free age- and sex-matched healthy subjects. Results: Patients with chronic OFP showed a significant reduction in their pain threshold compared to healthy subjects in all sites assessed. Greater reduction in pain threshold was recorded in patients with more severe psychological symptoms. Decreased alpha and increased gamma activity was recorded in central and frontal regions of all subjects, although no significant differences were observed between groups. Discussion: A general reduction in PPT was recorded in people who suffer from chronic OFP. This result may be explained by sensitization of the central nervous system due to chronic pain conditions. Abnormal EEG activity was recorded during painful stimulation compared to the relaxed condition in both chronic OFP subjects and healthy controls.

The brain and behavioral correlates of motor-related analgesia (MRA)

The human motor system has the capacity to act as an internal form of analgesia. Since the discovery of the potential influence of motor systems on analgesia in rodent models, clinical applications of targeting the motor system for analgesia have been implemented. However, a neurobiological basis for motor activation's effects on analgesia is not well defined. Motor-related analgesia (MRA) is a phenomenon wherein a decrease in pain symptoms can be achieved through either indirect or direct activation of the motor axis. To date, research has focused on (a) evaluating the pain-motor interaction as one focused on the acute protection from painful stimuli; (b) motor cortex stimulation for chronic pain; or (c) exercise as a method of improving chronic pain in animal and human models. This review evaluates (1) current knowledge surrounding how pain interferes with canonical neurological performance throughout the motor axis; and (2) the physiological basis for motor-related analgesia as a means to reduce pain symptom loads for patients. A proposal for future research directions is provided.

NIRS measures in pain and analgesia: Fundamentals, features, and function

Current pain assessment techniques based only on clinical evaluation and self-reports are not objective and may lead to inadequate treatment. Having a functional biomarker will add to the clinical fidelity, diagnosis, and perhaps improve treatment efficacy in patients. While many approaches have been deployed in pain biomarker discovery, functional near-infrared spectroscopy (fNIRS) is a technology that allows for non-invasive measurement of cortical hemodynamics. The utility of fNIRS is especially attractive given its ability to detect specific changes in the somatosensory and high-order cortices as well as its ability to measure (1) brain function similar to functional magnetic resonance imaging, (2) graded responses to noxious and innocuous stimuli, (3) analgesia, and (4) nociception under anesthesia. In this review, we evaluate the utility of fNIRS in nociception/pain with particular focus on its sensitivity and specificity, methodological advantages and limitations, and the current and potential applications in various pain conditions. Everything considered, fNIRS technology could enhance our ability to evaluate evoked and persistent pain across different age groups and clinical populations.

Motor Imagery Performance and Tactile Spatial Acuity: Are They Altered in People with Frozen Shoulder?

Frozen shoulder (adhesive capsulitis) is a severe chronic pain condition that is not well understood and current treatment is suboptimal. In several other chronic pain conditions motor imagery and tactile acuity deficits are present, which are thought to represent associated neuroplastic changes. The aims of this study were to determine if motor imagery performance assessed by the left/right judgement task, and tactile acuity assessed by two-point discrimination, are altered in people with unilateral frozen shoulder. In this cross-sectional, prospective study eighteen adults diagnosed with frozen shoulder in a physiotherapy clinic setting completed a left/right judgement task, response times (RT) and accuracy for the left/right judgement task were determined. Next, tactile acuity over both shoulders was assessed with a novel, force-standardised two-point discrimination test. Results corresponding to the affected side were compared to the pain free shoulder; Left/right judgement task: mean RT (SD) corresponding to the affected shoulder was significantly slower than RT for the healthy shoulder (p = 0.031). There was no side-to-side difference in accuracy (p > 0.05). Neither RT nor accuracy was related to pain/disability scores or duration of symptoms (p > 0.05). Two-point discrimination: mean two-point discrimination threshold of the affected shoulder was significantly larger than the contralateral healthy shoulder (p < 0.001). Two-point discrimination threshold was not related to pain/disability scores or pain duration (p > 0.05); One explanation for these findings is altered sensorimotor processing and/or disrupted sensorimotor cortex representations of the affected shoulder. A case then exists for the use of treatments aimed at reversing these changes, training the brain to reduce chronic shoulder pain.

Relationship Between Intensity of Neck Pain and Disability and Shoulder Pain and Disability in Individuals With Subacromial Impingement Symptoms: A Cross-Sectional Study

OBJECTIVE

This study aimed to verify a possible relationship between shoulder disability and shoulder pain intensity and the variables related to cervical-spine dysfunction, and determine which of these can differentiate moderate to severe shoulder pain (>4 on a numerical rating scale [NRS]) from mild shoulder pain (≤4 on the NRS) in individuals with subacromial impingement symptoms.

METHODS

One hundred and forty volunteers with shoulder pain were evaluated. Demographic information and variables related to the shoulder and neck were collected. Self-reported pain and disability of the shoulder and cervical spine were measured using the Shoulder Pain and Disability Index (SPADI) and Neck Disability Index (NDI) questionnaires, respectively. An NRS was used to measure pain in the shoulder and cervical spine. A purposeful modeling strategy was used to determine the best model to predict shoulder disability and shoulder pain (dependent variables). Multiple logistic regression analysis followed by receiver operating curve analysis was used to determine which variables better differentiated moderate to severe shoulder pain from mild shoulder pain.

RESULTS

Variables such as Neck Disability Index (NDI) score (β = 1.09, P = .00) and age (β = -0.19, P = .03) were associated with the total SPADI score. Neck pain was significantly associated with shoulder pain (β = 0.40, P = .00). The combination of variables predicting moderate to severe shoulder pain was total SPADI score (odds ratio [OR] = 1.15, P = .003), neck pain (OR = 3.20, P = .04), and age (OR = 1.01, P = .05).

CONCLUSION

Our results demonstrate the important connection between shoulder- and neck-related symptoms in individuals with subacromial impingement symptoms.

External rotator strength deficits in non-athletic people with rotator cuff related shoulder pain are not associated with pain intensity or disability levels

BACKGROUND

Strength deficits are often reported in people with rotator cuff related shoulder pain. However, these have mainly been tested in athletic populations and pain interference with testing has not been considered.

OBJECTIVES

To examine strength without pain interference in non-athletic people with rotator cuff related shoulder pain and its association with pain intensity and disability.

DESIGN

Cross-sectional study.

METHODS

Sixty-seven participants with rotator cuff related shoulder pain were assessed for isometric strength of shoulder external rotator and internal rotator muscles without pain interference with a hand-held dynamometer. Strength was normalized (%body weight). Differences in external and internal rotation strength and external:internal rotator strength ratio between symptomatic and asymptomatic sides were examined (Independent t-tests, Wilcoxon rank sum tests). Spearman's rank correlation coefficients were used to examine associations between strength and pain and disability levels.

RESULTS

There was no significant difference in internal rotator strength normalized to body weight between symptomatic and asymptomatic sides. There was a significant difference in external rotator strength normalized to body weight (p < .001) and external:internal ratio (p < .001) between sides. No significant correlations were found between strength and pain or disability levels.

CONCLUSION

Non-athletic people with rotator cuff related shoulder pain had external rotator strength deficits without pain interference during strength testing, which were not associated with pain and disability levels.

Strength and Power Training in Rehabilitation: Underpinning Principles and Practical Strategies to Return Athletes to High Performance

Injuries have a detrimental impact on team and individual athletic performance. Deficits in maximal strength, rate of force development (RFD), and reactive strength are commonly reported following several musculoskeletal injuries. This article first examines the available literature to identify common deficits in fundamental physical qualities following injury, specifically strength, rate of force development and reactive strength. Secondly, evidence-based strategies to target a resolution of these residual deficits will be discussed to reduce the risk of future injury. Examples to enhance practical application and training programmes have also been provided to show how these can be addressed.

DACC Resting State Functional Connectivity as a Predictor of Pain Symptoms Following Motor Vehicle Crash: A Preliminary Investigation

There is significant heterogeneity in pain outcomes following motor vehicle crashes (MVCs), such that a sizeable portion of individuals develop symptoms of chronic pain months after injury while others recover. Despite variable outcomes, the pathogenesis of chronic pain is currently unclear. Previous neuroimaging work implicates the dorsal anterior cingulate cortex (dACC) in adaptive control of pain, while prior resting state functional magnetic resonance imaging studies find increased functional connectivity (FC) between the dACC and regions involved in pain processing in those with chronic pain. Hyper-connectivity of the dACC to regions that mediate pain response may therefore relate to pain severity. The present study completed rsfMRI scans on N = 22 survivors of MVCs collected within 2 weeks of the incident to test whole-brain dACC-FC as a predictor of pain severity 6 months later. At 2 weeks, pain symptoms were predicted by positive connectivity between the dACC and the premotor cortex. Controlling for pain symptoms at 2 weeks, pain symptoms at 6 months were predicted by negative connectivity between the dACC and the precuneus. Previous research implicates the precuneus in the individual subjective awareness of pain. Given a relatively small sample size, approximately half of which did not experience chronic pain at 6 months, findings warrant replication. Nevertheless, this study provides preliminary evidence of enhanced dACC connectivity with motor regions and decreased connectivity with pain processing regions as immediate and prospective predictors of pain following MVC. PERSPECTIVE: This article presents evidence of distinct neural vulnerabilities that predict chronic pain in MVC survivors based on whole-brain connectivity with the dorsal anterior cingulate cortex.