Left dorsolateral prefrontal cortex repetitive transcranial magnetic stimulation reduces the development of long-term muscle pain

Association between aberrant brain activity and pain in patients with primary osteoporotic pain: aresting-state fMRI study

Studies have shown that chronic pain is associated with altered brain activity, while the pathological mechanism of Primary osteoporotic pain (POPP) is still unclear. MRI data and visual analogue scale (VAS) scores of 15 POPP patients and 16 HCs were collected. MRI data were preprocessed and then regional homogeneity (ReHo) and amplitude of low-frequency fluctuation (ALFF) values were calculated and compared between groups. Moreover, the correlations between ReHo and ALFF values of impaired brain regions and VAS scores were evaluated. Reduced ReHo values were found in the left medial superior frontal gyrus, middle frontal gyrus, opercular part of inferior frontal gyrus and right dorsolateral superior frontal gyrus of POPP patients. Increased ReHo values were detected in the left dorsolateral superior frontal gyrus and right middle frontal gyrus. Reduced ALFF values were identified in the left dorsolateral superior frontal gyrus, medial superior frontal gyrus, orbital part of middle frontal gyrus, opercular part of inferior frontal gyrus and right dorsolateral superior frontal gyrus. Increased ALFF values were observed in the right middle frontal gyrus and triangular part of inferior frontal gyrus. Negative correlations were identified between ReHo values of the left middle frontal gyrus and VAS scores in the patient group. In conclusion, the prefrontal dysfunction may be related to the occurrence of POPP. In addition, the left middle frontal gyrus can be used as an indicator to evaluate the severity of pain in patients with POPP.

The effects of virtual reality neuroscience-based therapy on clinical and neuroimaging outcomes in patients with chronic back pain: a randomized clinical trial

ABSTRACT

Chronic pain remains poorly managed. The integration of immersive technologies (ie, virtual reality [VR]) with neuroscience-based principles may provide effective pain treatment by targeting cognitive and affective neural processes that maintain pain and therefore potentially changing neurobiological circuits associated with pain chronification and amplification. We tested the effectiveness of a novel VR neuroscience-based therapy (VRNT) to improve pain-related outcomes in n = 31 participants with chronic back pain, evaluated against usual care (waitlist control; n = 30) in a 2-arm randomized clinical trial (NCT04468074). We also conducted pre-treatment and post-treatment MRI to test whether VRNT affects brain networks previously linked to chronic pain and treatment effects. Compared with the control condition, VRNT led to significantly reduced pain intensity (g = 0.63) and pain interference (g = 0.84) at post-treatment vs pre-treatment, with effects persisting at 2-week follow-up. These improvements were partially mediated by reduced kinesiophobia and pain catastrophizing. Several secondary clinical outcomes were also improved by VRNT, including disability, quality of life, sleep, and fatigue. In addition, VRNT was associated with increases in dorsomedial prefrontal functional connectivity with the superior somatomotor, anterior prefrontal and visual cortices, and decreased white matter fractional anisotropy in the corpus callosum adjacent to the anterior cingulate, relative to the control condition. Thus, VRNT showed preliminary efficacy in significantly reducing pain and improving overall functioning, possibly through changes in somatosensory and prefrontal brain networks.

Prolonged continuous theta burst stimulation increases motor corticospinal excitability and intracortical inhibition in patients with neuropathic pain: An exploratory, single-blinded, randomized controlled trial

OBJECTIVES

A new paradigm for Transcranial Magnetic Stimulation (TMS), referred to as prolonged continuous theta burst stimulation (pcTBS), has recently received attention in the literature because of its advantages over high frequency repetitive TMS (HF-rTMS). Clinical advantages include less time per intervention session and the effects appear to be more robust and reproducible than HF-rTMS to modulate cortical excitability. HF-rTMS targeted at the primary motor cortex (M1) has demonstrated analgesic effects in patients with neuropathic pain but their mechanisms of action are unclear and pcTBS has been studied in healthy subjects only. This study examined the neural mechanisms that have been proposed to play a role in explaining the effects of pcTBS targeted at the M1 and DLPFC brain regions in neuropathic pain (NP) patients with Type 2 diabetes.

METHODS

Forty-two patients with painful diabetic neuropathy were randomized to receive a single session of pcTBS targeted at the left M1 or left DLPFC. pcTBS stimulation consisted of 1,200 pulses delivered in 1 min and 44 s with a 35-45 min gap between sham and active pcTBS stimulation. Both the activity of the descending pain system which was examined using conditioned pain modulation and the activity of the ascending pain system which was assessed using temporal summation of pain were recorded using a handheld pressure algometer by measuring pressure pain thresholds. The amplitude of the motor evoked potential (MEP) was used to measure motor corticospinal excitability and GABA activity was assessed using short (SICI) and long intracortical inhibition (LICI). All these measurements were performed at baseline and post-pcTBS stimulation.

RESULTS

Following a single session of pcTBS targeted at M1 and DLPFC, there was no change in BPI-DN scores and on the activity of the descending (measured using conditioned pain modulation) and ascending pain systems (measured using temporal summation of pain) compared to baseline but there was a significant improvement of >13% in perception of acute pain intensity, increased motor corticospinal excitability (measured using MEP amplitude) and intracortical inhibition (measured using SICI and LICI).

CONCLUSION

In patients with NP, a single session of pcTBS targeted at the M1 and DLPFC modulated the neurophysiological mechanisms related to motor corticospinal excitability and neurochemical mechanisms linked to GABA activity, but it did not modulate the activity of the ascending and descending endogenous modulatory systems. In addition, although BPI-DN scores did not change, there was a 13% improvement in self-reported perception of acute pain intensity.

The Effects of Virtual Reality Neuroscience-based Therapy on Clinical and Neuroimaging Outcomes in Patients with Chronic Back Pain: A Randomized Clinical Trial

Chronic pain remains poorly managed. The integration of innovative immersive technologies (i.e., virtual reality (VR)) with recent neuroscience-based principles that position the brain as the key organ of chronic pain may provide a more effective pain treatment than traditional behavioral therapies. By targeting cognitive and affective processes that maintain pain and potentially directly changing neurobiological circuits associated with pain chronification and amplification, VR-based pain treatment has the potential for significant and long-lasting pain relief. We tested the effectiveness of a novel VR neuroscience-based therapy (VRNT) to improve pain-related outcomes in n = 31 participants with chronic back pain, evaluated against usual care (n = 30) in a 2-arm randomized clinical trial ( NCT04468074) . We also conducted pre- and post-treatment MRI to test whether VRNT affects brain networks previously linked to chronic pain and treatment effects. Compared to the control condition, VRNT led to significantly reduced pain intensity (g = 0.63) and pain interference (g = 0.84) at post-treatment vs. pre-treatment, with effects persisting at 2-week follow-up. The improvements were partially mediated by reduced kinesiophobia and pain catastrophizing. Several secondary clinical outcomes were also improved, including disability, quality of life, sleep, and fatigue. In addition, VRNT was associated with modest increases in functional connectivity of the somatomotor and default mode networks and decreased white matter fractional anisotropy in the corpus callosum adjacent to anterior cingula, relative to the control condition. This, VRNT showed preliminary efficacy in significantly reducing pain and improving overall functioning, possibly via changes in somatosensory and prefrontal brain networks.

Extensive Sensorimotor Training Predetermines Central Pain Changes During the Development of Prolonged Muscle Pain

Repetitive movements (RM) are a main risk factor for musculoskeletal pain, which is partly explained by the overloading of musculoskeletal structures. However, RM may also drive brain plasticity, leading to maladaptive changes in sensorimotor areas and altered pain processing. This study aimed to understand whether individuals performing extensive RM (musicians) exhibit altered brain processing to prolonged experimental muscle pain. Nineteen healthy musicians and 20 healthy nontrained controls attended 3 sessions (Day 1-Day 3-Day 8). In each session, event-related potentials (ERPs) to non-nociceptive superficial and nociceptive intraepidermal electrical stimulation, reaction times, electrical detection thresholds, and pressure pain thresholds (PPTs) were recorded. In all participants, prolonged muscle pain was induced by intramuscular injection of nerve growth factor (NGF) into the right first dorsal interosseous muscle at the end of Day1. Pain intensity was assessed on a numerical rating scale (NRS) and was lower in musicians compared to non-musicians (P < .007). Moreover, in musicians, the higher amount of weekly training was associated with lower NRS pain scores on Day 3 to Day 8 (P < .037). Compared with Day1, NGF reduced PPTs on Day 3 to Day 8 (P < .001) and non-nociceptive P200 and P300 ERP amplitudes on Day 8 (P < .044) in both groups. Musicians compared to controls showed secondary hyperalgesia to electrical stimulation on Day 3 to Day 8 (P < .004) and reduced nociceptive P200 ERP amplitudes on Day 8 (P < .005). Across participants, ERP components correlated with pain detection reaction times, sensitivity (PPTs and electrical detection thresholds), and severity (NRS), (all P < .043). These results show that repetitive sensorimotor training leads to brain changes in the processing of prolonged pain, biasing the cortical response to nociceptive inputs. PERSPECTIVE: Repetitive sensorimotor training may increase the responsiveness of nociceptive inputs during the development of prolonged muscle pain. These novel data highlight the role of repetitive sensorimotor practice as a source for interindividual variability in central pain processing.

Decreased Default Mode Network Connectivity Following 24 Hours of Capsaicin-induced Pain Persists During Immediate Pain Relief and Facilitation

Prolonged experimental pain models can help assess cortical mechanisms underlying the transition from acute to chronic pain such as resting-state functional connectivity (rsFC), especially in early stages. This crossover study determined the effects of 24-hour-capsaicin-induced pain on the default mode network rsFC, a major network in the dynamic pain connectome. Electroencephalographic rsFC measured by Granger causality was acquired from 24 healthy volunteers (12 women) at baseline, 1hour, and 24hours following the application of a control or capsaicin patch on the right forearm. The control patch was received maximum 1 week before the capsaicin patch. Following 24hours, the patch was cooled and later heated to assess rsFC changes in response to pain relief and facilitation, respectively. Compared to baseline, decreased rsFC at alpha oscillations (8-10Hz) was found following 1hour and 24hours of capsaicin application for connections projecting from medial prefrontal cortex (mPFC) and right angular gyrus (rAG) but not left angular gyrus (lAG) or posterior cingulate cortex (PCC): mPFC-PCC (1hour:P < .001, 24hours:P = .002), mPFC-rAG (1hour:P < .001, 24hours:P = .001), rAG-mPFC (1hour:P < .001, 24hours:P = .001), rAG-PCC (1hour:P < .001, 24hours:P = .004). Comparable decreased rsFC following 1hour and 24hours (P≤0.008) was found at beta oscillations, however, decreased projections from PCC were also found: PCC-rAG (P≤0.005) and PCC-lAG (P≤0.006). Pain NRS scores following 24hours (3.7±0.4) was reduced by cooling (0.3±0.1, P = .004) and increased by heating (4.8±0.6, P = .016). However, neither cooling nor heating altered rsFC. This study shows that 24hours of experimental pain induces a robust decrease in DMN connectivity that persists during pain relief or facilitation suggesting a possible shift to attentional and emotional processing in persistent pain. PERSPECTIVE: This article shows decreased DMN connectivity that might reflect possible attentional and emotional changes during acute and prolonged pain. Understanding these changes could potentially help clinicians in developing therapeutic methods that can better target these attentional and emotional processes before developing into more persistent states.

Acute improvement in the attention network with repetitive transcranial magnetic stimulation in Parkinson's disease

PURPOSE

To investigate the effect of two weeks of repetitive transcranial magnetic stimulation (rTMS) on the attention network in Parkinson's disease (PD) patients.

MATERIALS AND METHODS

Sixty PD patients were randomly divided into equal-sized active- and sham-rTMS groups. Executive function was assessed by neuropsychological tests including the Trail-Making Test (TMT), word fluency test, digit span, Wisconsin Card Sorting Test (WCST) and Stroop test. The attention network was evaluated by the attention network test (ANT). rTMS (5 Hz) was applied over the left dorsolateral prefrontal cortex (DLPFC) in the active-rTMS group, and the sham-rTMS group underwent sham stimulation, both for two weeks. All tests were performed before and after rTMS.

RESULTS

After active rTMS, nonparametric analysis revealed significant improvements in categories completed (CC) (p < 0.001) in the WCST and reaction times (RTs) in part 3 (p = 0.002) and the Stroop interference effect (SIE) (p < 0.001) in the Stroop test. Regarding the ANT, the RTs of the executive control network were significantly reduced (p < 0.001). There was no significant change after sham rTMS.

CONCLUSIONS

In the short term, in PD patients, rTMS improved the executive control network involved in resolving conflicting information. However, it showed milder effects on neuropsychological test outcomes assessing executive function, which may involve different neuromechanisms.Implications for rehabilitationCognitive impairment is common in patients with Parkinson's disease (PD), and it is related to functional disability and reduced quality of life.Attention is a main component of the cognitive system, and attention deficits are responsible for disability.This study demonstrates that rTMS is beneficial for cognitive rehabilitation in PD, as patients showed improved performance on the attention network test and neuropsychological tests.

Non-invasive brain stimulation and pain neuroscience education in the cognitive-affective treatment of chronic low back pain: Evidence and future directions

Chronic low back pain (CLBP) is among the leading causes of disability worldwide. Beyond the physical and functional limitations, people's beliefs, cognitions, and perceptions of their pain can negatively influence their prognosis. Altered cognitive and affective behaviors, such as pain catastrophizing and kinesiophobia, are correlated with changes in the brain and share a dynamic and bidirectional relationship. Similarly, in the presence of persistent pain, attentional control mechanisms, which serve to organize relevant task information are impaired. These deficits demonstrate that pain may be a predominant focus of attentional resources, leaving limited reserve for other cognitively demanding tasks. Cognitive dysfunction may limit one's capacity to evaluate, interpret, and revise the maladaptive thoughts and behaviors associated with catastrophizing and fear. As such, interventions targeting the brain and resultant behaviors are compelling. Pain neuroscience education (PNE), a cognitive intervention used to reconceptualize a person's pain experiences, has been shown to reduce the effects of pain catastrophizing and kinesiophobia. However, cognitive deficits associated with chronic pain may impact the efficacy of such interventions. Non-invasive brain stimulation (NIBS), such as transcranial direct current stimulation (tDCS) or repetitive transcranial magnetic stimulation (rTMS) has been shown to be effective in the treatment of anxiety, depression, and pain. In addition, as with the treatment of most physical and psychological diagnoses, an active multimodal approach is considered to be optimal. Therefore, combining the neuromodulatory effects of NIBS with a cognitive intervention such as PNE could be promising. This review highlights the cognitive-affective deficits associated with CLBP while focusing on current evidence for cognition-based therapies and NIBS.

Altered anterior insula functional connectivity in adolescent and young women with endometriosis-associated pain: Pilot resting-state fMRI study

BACKGROUND

Endometriosis is the leading cause of chronic pelvic pain. Alterations in brain functional connectivity have been reported in adult women with endometriosis-associated pain (EAP), however, it is still unknown if similar patterns of changes exist in adolescents.

METHODS

In this pilot study, resting-state fMRI scans were obtained from 11 adolescent and young women with EAP and 14 healthy female controls. Using a seed-to-voxel approach, we investigated functional connectivity between the anterior insula, medial prefrontal cortex, and the rest of the brain. Furthermore, we explored whether potential functional connectivity differences were correlated with clinical characteristics including disease duration, pain intensity, and different psychosocial factors (pain catastrophizing, fear of pain, functional disability, anxiety, and depression).

RESULTS

Our findings revealed that patients with EAP demonstrated significantly decreased connectivity between the right anterior insula and two clusters: one in the right cerebellum, and one in the left middle frontal gyrus compared to controls. Additionally, functional connectivity between the right anterior insula and the right cerebellum was positively associated with pain intensity levels. In patients with EAP, brain changes were also correlated with state anxiety and fear of pain.

CONCLUSIONS

Our results are relevant not only for understanding the brain characteristics underlying EAP at a younger age, but also in enhancing future pain treatment efforts by supporting the involvement of the central nervous system in endometriosis.

Systematic Review and Meta-Analysis of High-Frequency rTMS over the Dorsolateral Prefrontal Cortex .on Chronic Pain and Chronic-Pain-Accompanied Depression

The effect of high-frequency (HF) repetitive transcranial magnetic stimulation (rTMS) on the dorsolateral prefrontal cortex (DLPFC) can relieve chronic pain and accompanying depressive symptoms. However, in recent years, some high-quality studies have challenged this view. Therefore, it is necessary to update the data and analyze the effects of HF rTMS on the DLPFC on chronic pain and accompanying depression. We performed a systematic review and meta-analysis to evaluate the effect of HF rTMS on the DLPFC on chronic pain and accompanying depression. We searched PubMed, Medline, Web of Science, and Cochrane through September 2021. The search strings searched were : "pain" AND ("TMS" OR "transcranial magnetic stimulation") AND "prefrontal cortex". The inclusion criteria according to PICOS was as follows: P, patient with chronic pain; I, HF (≥5 Hz) rTMS on the DLPFC; C, included a sham treatment condition; O, pain indicators; S, pre-/poststudies, crossover, or parallel-group. We extracted the pain and accompanying depression evaluation indicators. The short-term analgesic effect of HF rTMS over the left DLPFC is not significant (WMD = 0.34, 95% CI: [-1.60, 2.28]) but has a significant mid-term and long-term analgesic effect on chronic pain (WMD = -0.50, 95% CI: [-0.99, -0.01]; WMD = -1.10, 95% CI: [-2.00, -0.19], respectively). HF rTMS over the DLPFC can effectively alleviate the depressive symptoms of patients with chronic pain (WMD = -0.83, 95% CI: [-3.01, 1.36]). Thus, HF rTMS on the left DLPFC can relieve chronic pain and accompanying depressive symptoms.

Repetitive transcranial magnetic stimulation regulates neuroinflammation, relieves hyperalgesia and reverses despair-like behaviour in chronic constriction injury rats

Repetitive transcranial magnetic stimulation (rTMS) could effectively relieve the pain and depression in neuropathic pain (NP) patients. However, the specific treatment parameters and exact mechanism are still unclear. Our purpose is to observe the effects of rTMS on pain and despair-like behaviour in chronic constriction injury (CCI) rats and explore its possible mechanism. Thirty-two 8-week-old male Sprague-Dawley rats were randomly divided into four groups: sham operation group (S, n = 8), CCI group (n = 8), 1 Hz-rTMS group (n = 8) and 10 Hz-rTMS group (n = 8). The rTMS was applied to the left dorsal anterior agranular insular (AId) 1 week after the operation, once a day, 5 days/week for 4 consecutive weeks. Mechanical hyperalgesia, despair-like behaviours and sciatic nerve function were used to evaluate the effects of rTMS. Besides, glucose metabolism, the metabotropic glutamate receptors 5 (mGluR5), N-Methyl-D-Aspartic acid receptor type 2B (NMDAR2B), tumour necrosis factor-α (TNF-α), interleukin-6 (Ll-6) and interleukin-1β (Ll-1β) in AId were tested to explore the possible mechanism. Compared with 1 Hz-rTMS, the rats of 10 Hz-rTMS had higher the mechanical hyperalgesia, higher sugar preference and shorter swimming immobility time. Besides, the expressions of mGluR5, NMDAR2B, TNF-α, Ll-1β and Ll-6 both in 1 Hz-rTMS and 10 Hz-rTMS groups were reduced compared with the CCI group; the 10 Hz-rTMS group had a more decrease than that of 1 Hz-rTMS. Furthermore, the [18]F-FDG uptake was lower than that in the 1 Hz-rTMS group. Compared with 1 Hz-rTMS, 10 Hz-rTMS could more effectively relieve mechanical hyperalgesia and reverse despair-like behaviour in rats. The mechanism could be related to regulating mGluR5/NMDAR2B-related inflammatory signalling pathways in the AId.

Neck Pain: Do We Know Enough About the Sensorimotor Control System?

Neck pain is a worldwide health problem. Clarifying the etiology and providing effective interventions are challenging for the multifactorial nature of neck pain. As an essential component of cervical spine function, the sensorimotor control system has been extensively studied in both healthy and pathological conditions. Proprioceptive signals generated from cervical structures are crucial to normal cervical functions, and abnormal proprioception caused by neck pain leads to alterations in neural plasticity, cervical muscle recruitment and cervical kinematics. The long-term sensorimotor disturbance and maladaptive neural plasticity are supposed to contribute to the recurrence and chronicity of neck pain. Therefore, multiple clinical evaluations and treatments aiming at restoring the sensorimotor control system and neural plasticity have been proposed. This paper provides a short review on neck pain from perspectives of proprioception, sensorimotor control system, neural plasticity and potential interventions. Future research may need to clarify the molecular mechanism underlying proprioception and pain. The existing assessment methods of cervical proprioceptive impairment and corresponding treatments may need to be systematically reevaluated and standardized. Additionally, new precise motor parameters reflecting sensorimotor deficit and more effective interventions targeting the sensorimotor control system or neural plasticity are encouraged to be proposed.

Multichannel transcranial direct current stimulation over the left dorsolateral prefrontal cortex may modulate the induction of secondary hyperalgesia, a double-blinded cross-over study in healthy volunteers

Background

Central sensitization is thought to play a critical role in the development of chronic pain, and secondary mechanical hyperalgesia is considered one of its hall-mark features. Consequently, interventions capable of modulating its development could have important therapeutic value. Non-invasive neuromodulation of the left dorsolateral prefrontal cortex (DLPFC) has shown potential to reduce pain, both in healthy volunteers and in patients. Whether it can modulate the induction of central sensitization, however, is less well known.

Objective

To determine whether multifocal transcranial direct current stimulation (tDCS) targeting the left DLPFC affects the development of secondary mechanical hyperalgesia.

Methods

In this within-subjects, cross-over, double-blinded study, eighteen healthy volunteers participated in three experimental sessions. After 20 minutes of either anodal, cathodal, or sham multichannel tDCS over the left DLPFC, secondary mechanical hyperalgesia was induced using high-frequency electrical stimulation (HFS) of the volar forearm. We assessed intensity of perception to 128 mN mechanical pinprick stimuli at baseline and up to 240 minutes after HFS. We also mapped the area of mechanical hyperalgesia.

Results

HFS resulted in a robust and unilateral increase in the intensity of perception to mechanical pinprick stimuli at the HFS arm, which was not different between tDCS stimulation conditions. However, the area of hyperalgesia was reduced after anodal tDCS compared to sham.

Conclusion

Anodal tDCS over the left DLPFC modestly modulates the size of the HFS-induced area of secondary mechanical hyperalgesia, suggesting that non-invasive neuromodulation targeting the left DLPFC may be a potential intervention to limit the development of central sensitization.

Tonic pain alters functional connectivity of the descending pain modulatory network involving amygdala, periaqueductal gray, parabrachial nucleus and anterior cingulate cortex

INTRODUCTION

Resting state functional connectivity (FC) is widely used to assess functional brain alterations in patients with chronic pain. However, reports of FC accompanying tonic pain in pain-free persons are rare. A network we term the Descending Pain Modulatory Network (DPMN) is implicated in healthy and pathologic pain modulation. Here, we evaluate the effect of tonic pain on FC of specific nodes of this network: anterior cingulate cortex (ACC), amygdala (AMYG), periaqueductal gray (PAG), and parabrachial nuclei (PBN).

METHODS

In 50 pain-free participants (30F), we induced tonic pain using a capsaicin-heat pain model. functional MRI measured resting BOLD signal during pain-free rest with a 32°C thermode and then tonic pain where participants experienced a previously warm temperature combined with capsaicin. We evaluated FC from ACC, AMYG, PAG, and PBN with correlation of self-report pain intensity during both states. We hypothesized tonic pain would diminish FC dyads within the DPMN.

RESULTS

Of all hypothesized FC dyads, only PAG and subgenual ACC was weakly altered during pain (F=3.34; p=0.074; pain-free>pain d=0.25). After pain induction sACC-PAG FC became positively correlated with pain intensity (R=0.38; t=2.81; p=0.007). Right PBN-PAG FC during pain-free rest positively correlated with subsequently experienced pain (R=0.44; t=3.43; p=0.001). During pain, this connection's FC was diminished (paired t=-3.17; p=0.0026). In whole-brain analyses, during pain-free rest, FC between left AMYG and right superior parietal lobule and caudate nucleus were positively correlated with subsequent pain. During pain, FC between left AMYG and right inferior temporal gyrus negatively correlated with pain. Subsequent pain positively correlated with right AMYG FC with right claustrum; right primary visual cortex and right temporo-occipitoparietal junction Conclusion: We demonstrate sACC-PAG tonic pain FC positively correlates with experienced pain and resting right PBN-PAG FC correlates with subsequent pain and is diminished during tonic pain. Finally, we reveal PAG- and right AMYG-anchored networks which correlate with subsequently experienced pain intensity. Our findings suggest specific connectivity patterns within the DPMN at rest are associated with subsequently experienced pain and modulated by tonic pain. These nodes and their functional modulation may reveal new therapeutic targets for neuromodulation or biomarkers to guide interventions.

Concurrent TMS-EEG to Reveal the Neuroplastic Changes in the Prefrontal and Insular Cortices in the Analgesic Effects of DLPFC-rTMS

The dorsolateral prefrontal cortex (DLPFC) is an important target for repetitive transcranial magnetic stimulation (rTMS) to reduce pain. However, the analgesic efficacy of DLPFC-rTMS needs to be optimized, in which the mechanisms of action remain unclear. Concurrent TMS and electroencephalogram (TMS-EEG) is able to evaluate neuroplastic changes beyond the motor cortex. Using TMS-EEG, this study was designed to investigate the local and distributed neuroplastic changes associated with DLPFC analgesia. Thirty-four healthy adults received DLPFC or sham stimulation in a randomized, crossover design. In each session, participants underwent cold pain and TMS-EEG assessment both before and after 10-Hz rTMS. We provide novel findings that DLPFC analgesia is associated with a smaller N120 amplitude in the contralateral prefrontal cortex as well as with a larger N120 peak in the ipsilateral insular cortex. Furthermore, there was a strong negative correlation between N120 changes of these two regions whereby the amplitude changes of this dyad were associated with increased pain threshold. In addition, DLPFC stimulation enhanced coherence between the prefrontal and somatosensory cortices oscillating in the gamma frequency. Overall, our data present novel evidence on local and distributed neuroplastic changes associated with DLPFC analgesia.

Brain Circuits Involved in the Development of Chronic Musculoskeletal Pain: Evidence From Non-invasive Brain Stimulation

It has been well-documented that the brain changes in states of chronic pain. Less is known about changes in the brain that predict the transition from acute to chronic pain. Evidence from neuroimaging studies suggests a shift from brain regions involved in nociceptive processing to corticostriatal brain regions that are instrumental in the processing of reward and emotional learning in the transition to the chronic state. In addition, dysfunction in descending pain modulatory circuits encompassing the periaqueductal gray and the rostral anterior cingulate cortex may also be a key risk factor for pain chronicity. Although longitudinal imaging studies have revealed potential predictors of pain chronicity, their causal role has not yet been determined. Here we review evidence from studies that involve non-invasive brain stimulation to elucidate to what extent they may help to elucidate the brain circuits involved in pain chronicity. Especially, we focus on studies using non-invasive brain stimulation techniques [e.g., transcranial magnetic stimulation (TMS), particularly its repetitive form (rTMS), transcranial alternating current stimulation (tACS), and transcranial direct current stimulation (tDCS)] in the context of musculoskeletal pain chronicity. We focus on the role of the motor cortex because of its known contribution to sensory components of pain via thalamic inhibition, and the role of the dorsolateral prefrontal cortex because of its role on cognitive and affective processing of pain. We will also discuss findings from studies using experimentally induced prolonged pain and studies implicating the DLPFC, which may shed light on the earliest transition phase to chronicity. We propose that combined brain stimulation and imaging studies might further advance mechanistic models of the chronicity process and involved brain circuits. Implications and challenges for translating the research on mechanistic models of the development of chronic pain to clinical practice will also be addressed.

Spinal cord neural activity of patients with fibromyalgia and healthy controls during temporal summation of pain: an fMRI study

The cause for the increased sensitivity of patients with fibromyalgia (FM) to painful stimuli is unclear but sensitization of dorsal horn spinal cord neurons has been suggested. There, critical changes of sensory information occur which depend on the plasticity of second-order neurons and descending pain modulation, including facilitation and inhibition. This study used repetitive stimuli that produce temporal-summation-of-second-pain (TSSP) and central sensitization, relevant mechanisms for patients with chronic pain. We examined spinal cord neural activation during TSSP in patients with FM and healthy controls (HC) and used its functional connectivity with several brainstem nuclei to model the observed blood-oxygen-level-dependent (BOLD) time-course with pain ratings. Sixteen HC and 14 FM participants received repetitive heat stimuli to the hand at 0.4 Hz to achieve TSSP during functional imaging with a 3 T-Philips Achieva MRI scanner. Stimuli were adjusted to each individual's pain sensitivity to achieve maximal pain ratings of 50 ± 10 on a numerical pain scale (0-100). Using a 16-channel neurovascular coil, multiple image series were obtained from the cervical spinal cord to the brainstem using single-shot turbo-spin echo sequences. During repetitive, sensitivity-adjusted heat stimuli, pain ratings of all subjects increased as predicted, consistent with TSSP. HC and FM participants had similar temporal patterns of spinal activation: initial BOLD increase followed by deactivation. Structural equation modeling showed that the observed spinal activity during TSSP was associated with more BOLD activity across/within the brainstem in FM subjects than HC, suggesting differences in pain modulation.NEW & NOTEWORTHY "Windup" and its behavioral correlate "temporal-summation-of-second pain" (TSSP) represent spinal cord mechanisms of pain augmentation associated with central sensitization and chronic pain. Fibromyalgia (FM) is a chronic pain disorder, where abnormal TSSP has been demonstrated. We used fMRI to study spinal cord and brainstem activation during TSSP. We characterized the time course of spinal cord and brainstem BOLD activity during TSSP which showed abnormal brainstem activity in patients with FM, possibly due to deficient pain modulation.

Pain relief associated with decreased oxyhemoglobin level in left dorsolateral prefrontal cortex

Pain in the elbow, shoulder, knee, lower back, and various other joints is relieved by adhesion of pyramidal thorn patches. To elucidate the pain relief mechanism induced by the patches, we established a quantitative method for estimating the pain reduction and investigated the brain regions that change in association with pain relief. We first attempted to quantify the pain relief using transcutaneous electric stimulation (TCES) and a visual analog scale (VAS), and then applied near-infrared spectroscopy (NIRS) to the prefrontal cortex, including the dorsolateral prefrontal cortex (DLPFC) and the orbitofrontal cortex (OFC). We also examined the salivary oxytocin levels, which are thought to reflect oxytocin secretion levels from the posterior pituitary in the brain. Application of pyramidal thorn patches to pain regions decreased the pain degree estimated using TCES and VAS. Oxyhemoglobin levels were likely to be decreased in the left DLPFC on the basis of NIRS measurements during patch treatment, suggesting that the left DLPFC is involved in pain relief. On the other hand, the salivary oxytocin levels varied widely. A potential reason for the varying salivary oxytocin levels is its utilization in the pain region as an analgesic agent. Our results suggest that the left DLPFC will become a target brain region for pain therapy.

Neuromodulation for Pain: A Comprehensive Survey and Systematic Review of Clinical Trials and Connectomic Analysis of Brain Targets

BACKGROUND

Chronic pain is a debilitating condition that imposes a tremendous burden on health-care systems around the world. While frontline treatments for chronic pain involve pharmacological and psychological approaches, neuromodulation can be considered for treatment-resistant cases. Neuromodulatory approaches for pain are diverse in both modality and target and their mechanism of action is incompletely understood.

OBJECTIVES

The objectives of this study were to (i) understand the current landscape of pain neuromodulation research through a comprehensive survey of past and current registered clinical trials (ii) investigate the network underpinnings of these neuromodulatory treatments by performing a connectomic mapping analysis of cortical and subcortical brain targets that have been stimulated for pain relief.

METHODS

A search for clinical trials involving pain neuromodulation was conducted using 2 major trial databases (ClinicalTrials.gov and the International Clinical Trials Registry Platform). Trials were categorized by variables and analyzed to gain an overview of the contemporary research landscape. Additionally, a connectomic mapping analysis was performed to investigate the network connectivity patterns of analgesic brain stimulation targets using a normative connectome based on a functional magnetic resonance imaging dataset.

RESULTS

In total, 487 relevant clinical trials were identified. Noninvasive cortical stimulation and spinal cord stimulation trials represented 49.3 and 43.7% of this count, respectively, while deep brain stimulation trials accounted for <3%. The mapping analysis revealed that superficial target connectomics overlapped with deep target connectomics, suggesting a common pain network across the targets.

CONCLUSIONS

Research for pain neuromodulation is a rapidly growing field. Our connectomic network analysis reinforced existing knowledge of the pain matrix, identifying both well-described hubs and more obscure structures. Further studies are needed to decode the circuits underlying pain relief and determine the most effective targets for neuromodulatory treatment.

High-frequency rTMS over the dorsolateral prefrontal cortex on chronic and provoked pain: A systematic review and meta-analysis

BACKGROUND

High-frequency rTMS over the dorsolateral prefrontal cortex (DLPFC) has demonstrated mixed effects on chronic and provoked pain.

OBJECTIVES/METHODS

In this study, a meta-analysis was conducted to characterise the potential analgesic effects of high-frequency rTMS over the DLPFC on both chronic and provoked pain.

RESULTS

A total of 626 studies were identified in a systematic search. Twenty-six eligible studies were included for the quantitative review, among which 17 modulated chronic pain and the remaining investigated the influence on provoked pain. The left side DLPFC was uniformly targeted in the chronic pain studies. While our data identified no overall effect of TMS across chronic pain conditions, there was a significant short-term analgesia in neuropathic pain conditions only (SMD = -0.87). In terms of long-lasting analgesia, there was an overall pain reduction in the midterm (SMD = -0.53, 24.6 days average) and long term (SMD = -0.63, 3 months average) post DLPFC stimulation, although these effects were not observed within specific chronic pain conditions. Surprisingly, the number of sessions was demonstrated to have no impact on rTMS analgesia. In the analysis of provoked pain, our data also indicated a significant analgesic effect following HF-rTMS over the DLPFC (SMD = -0.73). Importantly, we identified a publication bias in the studies of provoked pain but not for chronic pain conditions.

CONCLUSIONS

Overall, our findings support that HF-DLPFC stimulation is able to induce an analgesic effect in chronic pain and in response to provoked pain. These results highlight the potential of DLPFC-rTMS in the management of certain chronic pain conditions and future directions are discussed to enhance the potential long-term analgesic effects.

Effect of anodal high-definition transcranial direct current stimulation on the pain sensitivity in a healthy population: a double-blind, sham-controlled study

ABSTRACT

High-definition transcranial direct current stimulation (HD-tDCS) of brain areas related to pain processing may provide analgesic effects evident in the sensory detection and pain thresholds. The somatosensory sensitivity was assessed after HD-tDCS targeting the primary motor cortex (M1) and/or the dorsolateral prefrontal cortex (DLPFC). Eighty-one (40 females) subjects were randomly assigned to 1 of 4 anodal HD-tDCS protocols (20 minutes) applied on 3 consecutive days: Sham-tDCS, DLPFC-tDCS, M1-tDCS, and DLPFC&M1-tDCS (simultaneous transcranial direct current stimulation [tDCS] of DLPFC and M1). Subjects and experimenter were blinded to the tDCS protocols. The somatosensory sensitivity were assessed each day, before and after each tDCS by detection and pain thresholds to thermal and mechanical skin stimulation, vibration detection thresholds, and pressure pain thresholds. Subjects were effectively blinded to the protocol, with no significant difference in rates of whether they received real or placebo tDCS between the 4 groups. Compared with the Sham-tDCS, none of the active HD-tDCS protocols caused significant changes in detection or pain thresholds. Independent of tDCS protocols, pain and detection thresholds except vibration detection were increased immediately after the first tDCS protocol compared with baseline (P < 0.05). Overall, the active stimulation protocols were not able to induce significant modulation of the somatosensory thresholds in this healthy population compared with sham-tDCS. Unrelated to the HD-tDCS protocol, a decreased sensitivity was found after the first intervention, indicating a placebo effect or possible habituation to the quantitative sensory testing assessments. These findings add to the increasing literature of null findings in the modulatory effects of HD-tDCS on the healthy somatosensory system.

Repetitive non-invasive prefrontal stimulation reverses neuropathic pain via neural remodelling in mice

Chronic neuropathic pain presents a major challenge to pharmacological therapy and neurostimulation-based alternatives are gaining interest. Although invasive and non-invasive motor cortex stimulation has been the focus of several studies, very little is known about the potential of targeting the prefrontal cortex. This study was designed to elucidate the analgesic potential of prefrontal stimulation in a translational context and to uncover the neural underpinnings thereof. Here, we report that non-invasive, repetitive direct anodal current transcranial stimulation (tDCS) of the prefrontal cortex exerted analgesia in mice with neuropathic pain for longer than a week. When applied at chronic stages of neuropathic pain, prefrontal tDCS reversed established allodynia and suppressed aversion and anxiety-related behaviours. Activity mapping as well as in vivo electrophysiological analyses revealed that although the cortex responds to acute tDCS with major excitation, repetitive prefrontal tDCS brings about large-scale silencing of cortical activity. Different classes of different classes of GABAergic interneurons and classes of excitatory neurons differs dramatically between single, acute vs and repetitive tDCS. Repetitive prefrontal tDCS alters basal activity as well as responsivity of a discrete set of distant cortical and sub-cortical areas to tactile stimuli, namely the rostral anterior cingulate cortex, the insular cortex, the ventrolateral periaqueductal grey and the spinal dorsal horn. This study thus makes a strong case for harnessing prefrontal cortical modulation for non-invasive transcranial stimulation paradigms to achieve long-lasting pain relief in established neuropathic pain states and provides valuable insights gained on neural mechanistic underpinnings of prefrontal tDCS in neuropathic pain.

Transcranial Direct Current Stimulation Accelerates The Onset of Exercise-Induced Hypoalgesia: A Randomized Controlled Study

Exercise-induced hypoalgesia (EIH) describes acute reductions in pain that occur following exercise. Current evidence suggests that the magnitude of EIH is small-to-moderate at best, warranting exploration of novel avenues to bolster these effects. Transcranial direct current stimulation (tDCS) has been shown to relieve pain and represents a promising intervention that may enhance EIH. This study aimed to determine whether anodal tDCS of the primary motor cortex (M1) can augment EIH in healthy individuals experiencing experimentally-induced musculoskeletal pain. Twenty-four healthy subjects attended 2 experimental sessions ("Day 0" and "Day 2"). On Day 0, subjects were injected with nerve growth factor into their right extensor carpi radialis brevis to induce persistent elbow pain. On Day 2, each subject received active or sham tDCS over M1 followed by an isometric grip exercise. Pain intensity, muscle soreness, sensitivity (pressure pain thresholds), and conditioned pain modulation were assessed prior to the nerve growth factor injection, on Day 2 before tDCS, immediately post-exercise, and 15 minutes post-exercise. Active tDCS expedited the onset of EIH, inducing immediate reductions in pain intensity that were not present until 15 minutes post-exercise in the sham group. However, active tDCS did not reduce muscle soreness or sensitivity when compared to sham tDCS. PERSPECTIVE: These findings suggest that active tDCS accelerates the onset of EIH in healthy individuals experiencing experimentally-induced pain. This may represent a promising means of enhancing adherence to exercise protocols. However, larger randomised controlled trials in persistent pain populations are required to confirm the clinical impact of these findings.

Enhanced mindfulness-based stress reduction in episodic migraine: a randomized clinical trial with magnetic resonance imaging outcomes

We aimed to evaluate the efficacy of an enhanced mindfulness-based stress reduction (MBSR+) vs stress management for headache (SMH). We performed a randomized, assessor-blind, clinical trial of 98 adults with episodic migraine recruited at a single academic center comparing MBSR+ (n = 50) with SMH (n = 48). MBSR+ and SMH were delivered weekly by group for 8 weeks, then biweekly for another 8 weeks. The primary clinical outcome was reduction in headache days from baseline to 20 weeks. Magnetic resonance imaging (MRI) outcomes included activity of left dorsolateral prefrontal cortex (DLPFC) and cognitive task network during cognitive challenge, resting state connectivity of right dorsal anterior insula to DLPFC and cognitive task network, and gray matter volume of DLPFC, dorsal anterior insula, and anterior midcingulate. Secondary outcomes were headache-related disability, pain severity, response to treatment, migraine days, and MRI whole-brain analyses. Reduction in headache days from baseline to 20 weeks was greater for MBSR+ (7.8 [95% CI, 6.9-8.8] to 4.6 [95% CI, 3.7-5.6]) than for SMH (7.7 [95% CI 6.7-8.7] to 6.0 [95% CI, 4.9-7.0]) (P = 0.04). Fifty-two percent of the MBSR+ group showed a response to treatment (50% reduction in headache days) compared with 23% in the SMH group (P = 0.004). Reduction in headache-related disability was greater for MBSR+ (59.6 [95% CI, 57.9-61.3] to 54.6 [95% CI, 52.9-56.4]) than SMH (59.6 [95% CI, 57.7-61.5] to 57.5 [95% CI, 55.5-59.4]) (P = 0.02). There were no differences in clinical outcomes at 52 weeks or MRI outcomes at 20 weeks, although changes related to cognitive networks with MBSR+ were observed. Enhanced mindfulness-based stress reduction is an effective treatment option for episodic migraine.

Connectivity between the anterior insula and dorsolateral prefrontal cortex links early symptom improvement to treatment response

BACKGROUND

Early improvement (EI) following treatment with antidepressants is a widely reported predictor to the treatment response. This study aimed to identify the resting-state functional connectivity (rs-FC) and its related clinical features that link the treatment response at the time of EI.

METHODS

This study included 23 first-episode treatment-naive patients with MDD. After 2 weeks of antidepressant treatment, these patients received 3.0 Tesla resting-state functional magnetic resonance imaging scanning and were subgrouped into an EI group (N = 13) and a non-EI group (N = 10). Using the anterior insula (rAI) as a seed region, this study identified the rs-FC that were associated with both EI and the treatment response at week 12, and further tested the associations of the identified rs-FC with either the clinical features or the early symptom improvement.

RESULTS

Rs-FC between rAI and the left dorsolateral prefrontal cortex (dlPFC) was associated with EI (t₂₁ = -6.091, p = 0.022 after FDR correction for multiple comparisons). This rs-FC was also associated with an interaction between EI and the treatment response at the week 12 (t₂₁ = -5.361, p = 6.37e-5). Moreover, among the clinical features, this rs-FC was associated with the early symptom improvement in the insomnia, somatic symptoms, and anxiety symptoms, and these early symptom improvements were associated with the treatment response.

CONCLUSION

Rs-FC between the rAI and the left dlPFC played a crucial role in the early antidepressant effect, which linked the treatment response. The early treatment effect relating to rAI may represent an early symptom improvement in self-perceptual anxiety, somatic symptoms and insomnia.

Non-invasive Motor Cortex Neuromodulation Reduces Secondary Hyperalgesia and Enhances Activation of the Descending Pain Modulatory Network

Central sensitization is a driving mechanism in many chronic pain patients, and manifests as hyperalgesia and allodynia beyond any apparent injury. Recent studies have demonstrated analgesic effects of motor cortex (M1) stimulation in several chronic pain disorders, yet its neural mechanisms remain uncertain. We evaluated whether anodal M1 transcranial direct current stimulation (tDCS) would mitigate central sensitization as measured by indices of secondary hyperalgesia. We used a capsaicin-heat pain model to elicit secondary mechanical hyperalgesia in 27 healthy subjects. In an assessor and subject-blind randomized, sham-controlled, crossover trial, anodal M1 tDCS decreased the intensity of pinprick hyperalgesia more than cathodal or sham tDCS. To elucidate the mechanism driving analgesia, subjects underwent fMRI of painful mechanical stimuli prior to and following induction of the pain model, after receiving M1 tDCS. We hypothesized that anodal M1 tDCS would enhance engagement of a descending pain modulatory (DPM) network in response to mechanical stimuli. Anodal tDCS normalized the effects of central sensitization on neurophysiological responses to mechanical pain in the medial prefrontal cortex, pregenual anterior cingulate cortex, and periaqueductal gray, important regions in the DPM network. Taken together, these results provide support for the hypothesis that anodal M1-tDCS reduces central sensitization-induced hyperalgesia through the DPM network in humans.