Cortical representation of pain in primary sensory-motor areas (S1/M1)--a study using intracortical recordings in humans

Facilitation of Early and Middle Latency SEP after tDCS of M1: No Evidence of Primary Somatosensory Homeostatic Plasticity

Homeostatic plasticity is a mechanism that stabilizes cortical excitability within a physiological range. Most homeostatic plasticity protocols have primed and tested the homeostatic response of the primary motor cortex (M1). This study investigated if a homeostatic response could be recorded from the primary sensory cortex (S1) after inducing homeostatic plasticity in M1. In 31 healthy participants, homeostatic plasticity was induced over M1 with a priming and testing block of transcranial direct current stimulation (tDCS) in two different sessions (anodal and cathodal). S1 excitability was assessed by early (N20, P25) and middle-latency (N33-P45) somatosensory evoked potentials (SEP) extracted from 4 electrodes (CP5, CP3, P5, P3). Baseline and post-measures (post-priming, 0-min, 10-min, and 20-min after homeostatic induction) were taken. Anodal M1 homeostatic plasticity induction significantly facilitated the N20-P25, P45 peak, and N33-P45 early SEP components up to 20-min post-induction, without any indication of a homeostatic response (i.e., reduced SEP). Cathodal homeostatic induction did not induce any significant effect on early or middle latency SEPs. M1 homeostatic plasticity induction by anodal stimulation protocol to the primary motor cortex did not induce a homeostatic response in SEPs.

Contralateral acupuncture for migraine without aura: a randomized trial protocol with multimodal MRI

Introduction

Migraine is a common clinical disorder, ranks as the second most disabling disease worldwide, and often manifests with unilateral onset. Contralateral acupuncture (CAT), as a classical acupuncture method, has been proven to be effective in the treatment of migraine without aura (MWoA). However, its neural mechanisms have not been investigated using multimodal magnetic resonance imaging (MRI).

Methods and analysis

In this multimodal neuroimaging randomized trial, a total of 96 female MWoA participants and 30 female healthy controls (HCs) will be recruited. The 96 female MWoA participants will be randomized into three groups: Group A (CAT group), Group B [ipsilateral acupuncture (IAT) group], and Group C (sham CAT group) in a 1:1:1 allocation ratio. Each group will receive 30 min of treatment every other day, three times a week, for 8 weeks, followed by an 8-week follow-up period. The primary outcome is the intensity of the migraine attack. Data will be collected at baseline (week 0), at the end of the 8-week treatment period (weeks 1-8), and during the 8-week follow-up (weeks 9-16). Adverse events will be recorded. Multimodal MRI scans will be conducted at baseline and after 8-week treatment.

Discussion

This study hypothesized that CAT may treat MWoA by restoring pathological alterations in brain neural activity, particularly by restoring cross-integrated functional connectivity with periaqueductal gray (PAG) as the core pathological brain region. The findings will provide scientific evidence for CAT in the treatment of MWoA.

Ethics and dissemination

The Medical Ethics Committee of the Second Affiliated Hospital of Yunnan University of Chinese Medicine has given study approval (approval no. 2022-006). This trial has been registered with the Chinese Clinical Trials Registry (registration no. ChiCTR2300069456). Peer-reviewed papers will be used to publicize the trial's findings.

Clinical trial registration

https://clinicaltrials.gov/, identifier ChiCTR2300069456.

Effects of Repetitive-Transcranial Magnetic Stimulation (rTMS) in Fibromyalgia Syndrome: An Umbrella and Mapping Review

BACKGROUND

The main aim of this study was to assess the effects of repetitive-transcranial magnetic stimulation (rTMS) in patients with fibromyalgia (FMS).

METHODS

We systematically searched PubMed, PEDro, EMBASE, and CINAHL. Methodological quality was analyzed using the AMSTAR and ROBIS scales, and the strength of evidence was established according to the guidelines advisory committee grading criteria. A total of 11 systematic reviews were included. The assessed variables were pain intensity, depressive symptoms, anxiety, and general health.

RESULTS

Regarding pain intensity, it seems that high-frequency rTMS significantly reduces pain intensity at a 1-month follow-up when the primary motor cortex (M1) is stimulated. However, we cannot robustly conclude the same for low-frequency protocols. When we look at the combination of high and low-frequency rTMS, there seems to be a significant effect on pain intensity up to 1-week post-intervention, but after that point of follow-up, the results are controversial. Regarding depressive symptoms and anxiety, results showed that the effects of rTMS are almost non-existent. Finally, in regard to general health, results showed that rTMS caused significant post-intervention effects in a robust way. However, the results of the follow-ups are contradictory.

CONCLUSIONS

The results obtained showed that high-frequency rTMS applied on the M1 showed some effect on the variable of pain intensity with a limited quality of evidence. Overall, rTMS was shown to be effective in improving general health with moderate quality of evidence. Finally, rTMS was not shown to be effective in managing depressive symptoms and anxiety with a limited to moderate quality of evidence. PROSPERO number: This review was previously registered in PROSPERO (CRD42023391032).

Effects of hypocapnia and hypercapnia on human somatosensory processing

The present study investigated the effects of hypocapnia and hypercapnia on human somatosensory processing by utilizing somatosensory evoked magnetic fields (SEFs) with magnetoencephalography (MEG). Thirteen volunteers participated in two experiments separately to measure respiratory and cardiovascular data and SEFs. Both experiments consisted of a combination of normal and rapid respiratory rhythms and two inspiratory gas conditions (air and a hypercapnic gas); normal breathing with air (NB), rapid breathing with air (RB), normal breathing with the hypercapnic gas (NB+Gas), and rapid breathing with gas (RB+Gas). Partial pressures of end-tidal CO₂ (P_ETCO2) increased during inhaling the hypercapnic gas and decreased during RB, but the RB+Gas condition continued to cause elevated PETCO₂ compared with the baseline. Subsequently, middle cerebral artery blood (MCA) velocity using transcranial Doppler changed as well, while mean MCA velocity increased under the RB+Gas condition. The peak amplitude of the M60 component in SEFs was also significantly larger under with-gas than without-gas conditions, irrespective of the respiratory frequency. These results suggest that there is a close relationship between cerebral blood flow and neural activity of the M60 component in SEFs. This study provides evidence to further understanding on one of the neural mechanisms of hypercapnia.

Regional homogeneity alterations in multifrequency bands in patients with extracranial multi-organ tuberculosis: a prospective cross-sectional study

Background

This study aimed to clarify the spontaneous neural activity in the conventional frequency band (0.01-0.08 Hz) and 2 subfrequency bands (slow-4: 0.027-0.073 Hz; slow-5: 0.01-0.027 Hz) in patients with extracranial multi-organ tuberculosis (EMTB) through regional homogeneity (ReHo) analysis.

Methods

In all, 32 patients with EMTB and 31 healthy controls (HCs) were assessed by resting-state functional magnetic resonance imaging (rs-fMRI) scans to clarify the abnormal spontaneous neural activity through ReHo analysis in the conventional frequency band and 2 subfrequency bands.

Results

Compared with the HCs, the patients with EMTB exhibited decreased ReHo in the left postcentral gyrus [t=-4.79; 95% confidence interval (CI): -0.79 to -0.31] and the left superior cerebellum (t=-4.45; 95% CI: -0.54 to -0.21) in the conventional band. Conversely, increased ReHo was observed in the right middle occipital gyrus (t=3.94; 95% CI: 0.18-0.53). In the slow-4 band, patients with EMTB only exhibited decreased ReHo in the superior cerebellum (t=-4.69; 95% CI: -0.54 to -0.22); meanwhile, in the slow-5 band, these patients exhibited decreased ReHo in the right postcentral gyrus (t=-3.76; 95% CI: -0.74 to -0.21) and the left superior cerebellum (t=-5.20, 95% CI: -0.72 to -0.31). After Bonferroni correction, no significant correlation was observed between the ReHo values in clusters showing significant between-group differences and cognitive test scores.

Conclusions

ReHo showed abnormal synchronous neural activity in patients with EMTB in different frequency bands, which provides a novel understanding of the pathological mechanism of EMTB.

Effect of acute ankle experimental pain on lower limb motor control assessed by the modified star excursion balance test

Introduction

Following most musculoskeletal injuries, motor control is often altered. Acute pain has been identified as a potential contributing factor. However, there is little evidence of this interaction for acute pain following ankle sprains. As pain is generally present following this type of injury, it would be important to study the impact of acute pain on ankle motor control. To do so, a valid and reliable motor control test frequently used in clinical settings should be used. Therefore, the objective of this study was therefore to assess the effect of acute ankle pain on the modified Star Excursion Balance Test reach distance.

Methods

Using a cross-sectional design, 48 healthy participants completed the modified Star Excursion Balance Test twice (mSEBT1 and mSEBT2). Following the first assessment, they were randomly assigned to one of three experimental groups: Control (no stimulation), Painless (non-nociceptive stimulation) and Painful (nociceptive stimulation). Electrodes were placed on the right lateral malleolus to deliver an electrical stimulation during the second assessment for the Painful and Painless groups. A generalized estimating equations model was used to compare the reach distance between the groups/conditions and assessments.

Results

Post-hoc test results: anterior (7.06 ± 1.54%; p < 0.0001) and posteromedial (6.53 ± 1.66%; p < 0.001) directions showed a significant reach distance reduction when compared to baseline values only for the Painful group. Regarding the anterior direction, this reduction was larger than the minimal detectable change (5.87%).

Conclusion

The presence of acute pain during the modified Star Excursion Balance Test can affect performance and thus might interfere with the participant's lower limb motor control. As none of the participants had actual musculoskeletal injury, this suggests that pain and not only musculoskeletal impairments could contribute to the acute alteration in motor control.

Layer-specific pain relief pathways originating from primary motor cortex

The primary motor cortex (M1) is involved in the control of voluntary movements and is extensively mapped in this capacity. Although the M1 is implicated in modulation of pain, the underlying circuitry and causal underpinnings remain elusive. We unexpectedly unraveled a connection from the M1 to the nucleus accumbens reward circuitry through a M1 layer 6-mediodorsal thalamus pathway, which specifically suppresses negative emotional valence and associated coping behaviors in neuropathic pain. By contrast, layer 5 M1 neurons connect with specific cell populations in zona incerta and periaqueductal gray to suppress sensory hypersensitivity without altering pain affect. Thus, the M1 employs distinct, layer-specific pathways to attune sensory and aversive-emotional components of neuropathic pain, which can be exploited for purposes of pain relief.

Network Effects of Brain Lesions Causing Central Poststroke Pain

OBJECTIVE

This study was undertaken to test whether lesions causing central poststroke pain (CPSP) are associated with a specific connectivity profile, whether these connections are associated with metabolic changes, and whether this network aligns with neuromodulation targets for pain.

METHODS

Two independent lesion datasets were utilized: (1) subcortical lesions from published case reports and (2) thalamic lesions with metabolic imaging using 18F- fluorodeoxyglucose positron emission tomography-computed tomography. Functional connectivity between each lesion location and the rest of the brain was assessed using a normative connectome (n = 1,000), and connections specific to CPSP were identified. Metabolic changes specific to CPSP were also identified and related to differences in lesion connectivity. Therapeutic relevance of the network was explored by testing for alignment with existing brain stimulation data and by prospectively targeting the network with repetitive transcranial magnetic stimulation (rTMS) in 7 patients with CPSP.

RESULTS

Lesion locations causing CPSP showed a specific pattern of brain connectivity that was consistent across two independent lesion datasets (spatial r = 0.82, p < 0.0001). Connectivity differences were correlated with postlesion metabolism (r = -0.48, p < 0.001). The topography of this lesion-based pain network aligned with variability in pain improvement across 12 prior neuromodulation targets and across 32 patients who received rTMS to primary motor cortex (p < 0.05). Prospectively targeting this network with rTMS improved CPSP in 6 of 7 patients.

INTERPRETATION

Lesions causing pain are connected to a specific brain network that shows metabolic abnormalities and promise as a neuromodulation target. ANN NEUROL 2022;92:834-845.

Altered regional homogeneity of spontaneous brain activity in patients with toothache: A resting-state functional magnetic resonance imaging study

Toothache (TA) is a common and severe pain, but its effects on the brain are somewhat unclear. In this study, functional magnetic resonance imaging (fMRI) was used to compare regional homogeneity (ReHo) between TA patients and a normal control group and to explore the brain activity changes during TA, establishing the theoretical basis for the mechanism of neuropathic pain. In total, 20 TA patients and 20 healthy controls (HCs) were recruited and underwent assessment of pain, and then resting-state fMRI (rs-fMRI). The ReHo method was used to analyze the original whole-brain images. Pearson’s correlation analysis was used to assess the relationship between mean ReHo values in each brain region and clinical symptoms, and the receiver operating characteristic (ROC) curve was used to conduct correlation analysis on the brain regions studied. The ReHo values of the right lingual gyrus (RLG), right superior occipital gyrus (RSOG), left middle occipital gyrus (LMOG) and right postcentral gyrus (RPG) in the TA group were significantly higher than in HCs. The mean ReHo values in the RLG were positively correlated with the anxiety score (AS) (r = 0.723, p &lt; 0.001), depression score (DS) (r = 0.850, p &lt; 0.001) and visual analogue score (VAS) (r = 0.837, p &lt; 0.001). The mean ReHo values of RSOG were also positively correlated with AS (r = 0.687, p = 0.001), DS (r = 0.661, p = 0.002) and VAS (r = 0.712, p &lt; 0.001). The areas under the ROC curve of specific brain area ReHo values were as follows: RLG, 0.975; RSOG, 0.959; LMOG, 0.975; RPG, 1.000. Various degrees of brain activity changes reflected by ReHo values in different areas of the brain indicate the impact of TA on brain function. These findings may reveal related neural mechanisms underlying TA.

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.

Intensity-dependent modulation of cortical somatosensory processing during external, low-frequency peripheral nerve stimulation in humans

External low-frequency peripheral nerve stimulation (LFS) has been proposed as a novel method for neuropathic pain relief. Previous studies have reported that LFS elicits long-term depression-like effects on human pain perception when delivered at noxious intensities, whereas lower intensities are ineffective. To shed light on cortical regions mediating the effects of LFS, we investigated changes in somatosensory-evoked potentials (SEPs) during four LFS intensities. LFS was applied to the radial nerve (600 pulses, 1 Hz) of 24 healthy participants at perception (1 times), low (5 times), medium (10 times), and high intensities (15 times detection threshold). SEPs were recorded during LFS, and averaged SEPs in 10 consecutive 1-min epochs of LFS were analyzed using source dipole modeling. Changes in resting electroencephalography (EEG) were investigated after each LFS block. Source activity in the midcingulate cortex (MCC) decreased linearly during LFS, with greater attenuation at stronger LFS intensities, and in the ipsilateral operculo-insular cortex during the two lowest LFS stimulus intensities. Increased LFS intensities resulted in greater augmentation of contralateral primary sensorimotor cortex (SI/MI) activity. Stronger LFS intensities were followed by increased α (alpha, 9-11 Hz) band power in SI/MI and decreased θ (theta, 3-5 Hz) band power in MCC. Intensity-dependent attenuation of MCC activity with LFS is consistent with a state of long-term depression. Sustained increases in contralateral SI/MI activity suggests that effects of LFS on somatosensory processing may also be dependent on satiation of SI/MI. Further research could clarify if the activation of SI/MI during LFS competes with nociceptive processing in neuropathic pain.NEW & NOTEWORTHY Somatosensory-evoked potentials during low-frequency stimulation of peripheral nerves were examined at graded stimulus intensities. Low-frequency stimulation was associated with decreased responsiveness in the midcingulate cortex and increased responsiveness in primary sensorimotor cortex. Greater intensities were associated with increased midcingulate cortex θ band power and decreased sensorimotor cortex α band power. Results further previous evidence of an inhibition of somatosensory processing during and after low-frequency stimulation and point toward a potential augmentation of activity in somatosensory processing regions.

Effects of different modalities of afferent stimuli of the lumbo-sacral area on control of lumbar paravertebral muscles

Somatosensory feedback to the central nervous system is essential to plan, perform and refine spine motor control. However, the influence of somatosensory afferent input from the trunk on the motor output to trunk muscles has received little attention. The objective was to compare the effects of distinct modalities of afferent stimulation on the net motoneuron and corticomotor excitability of paravertebral muscles. Fourteen individuals were recruited. Modulation of corticospinal excitability (motor-evoked potential [MEP]) of paravertebral muscles was measured when afferent stimuli (cutaneous noxious and non-noxious, muscle contraction) were delivered to the trunk at 10 intervals prior to transcranial magnetic stimulation. Each peripheral stimulation was applied alone, and subsequent EMG modulation was measured to control for net motoneuron excitability. MEP modulation and MEP/EMG ratio were used as measures of corticospinal excitability with and without control of net motoneuron excitability, respectively. MEP and EMG modulation were smaller after evoked muscle contraction than after cutaneous noxious and non-noxious stimuli. MEP/EMG ratio was not different between stimulation types. Both MEP and EMG amplitudes were reduced after evoked muscle contraction, but not when expressed as MEP/EMG ratio. Noxious and non-noxious stimulation had limited impact on all variables. Distinct modalities of peripheral afferent stimulation of the lumbo-sacral area differently modulated responses of paravertebral muscles, but without an influence on corticospinal excitability with control of net motoneuron excitability. Muscle stimulation reduced paravertebral activity and was best explained by spinal mechanisms. The impact of afferent stimulation on back muscles differs from the effects reported for limb muscles.

Supraspinal Mechanisms Underlying Ocular Pain

Supraspinal mechanisms of pain are increasingly understood to underlie neuropathic ocular conditions previously thought to be exclusively peripheral in nature. Isolating individual causes of centralized chronic conditions and differentiating them is critical to understanding the mechanisms underlying neuropathic eye pain and ultimately its treatment. Though few functional imaging studies have focused on the eye as an end-organ for the transduction of noxious stimuli, the brain networks related to pain processing have been extensively studied with functional neuroimaging over the past 20 years. This article will review the supraspinal mechanisms that underlie pain as they relate to the eye.

Alteration of ankle proprioceptive threshold during gait in the presence of acute experimental pain

OBJECTIVE

Human gait requires complex somatosensory processing of various inputs such as proprioception. Proprioception can be altered in the presence of pain. This has been shown mostly during controlled tasks, thereby limiting the influence of external perturbations. While controlling the environment is sometimes warranted, it limits the ecological validity of the data. Using robotic orthoses to apply perturbations during movements seems a promising tool to functionally assess proprioception, where the complex somatosensory processing required in real-life situations is at play. The main objective of this study was to compare the proprioceptive threshold of healthy participants during gait in the presence and absence of an acute experimental pain.

METHODS

36 healthy participants walked on a treadmill while wearing a robotized ankle-foot orthosis (rAFO) around their right ankle. The rAFO applied torque perturbations of graded magnitudes during the swing phase of gait. Participants had to report the presence/absence of such perturbations, as a measure of proprioceptive threshold. Following initial assessment, they were randomly assigned to one of three experimental groups: Control (no stimulation), Painless (non-nociceptive stimulation) and Painful (nociceptive stimulation). Electrodes placed on the right lateral malleolus delivered an electrical stimulation during the second assessment for Painless and Painful groups. A Kruskal-Wallis was used to compare the percentage of change of the three groups between the two assessments.

RESULTS

A 31.80±32.94% increase in proprioceptive threshold, representing an increase of 1.3±1.2 Nm in the detection threshold, was observed for the Painful group only (p<0.005), with an effect size of 1.6.

CONCLUSION

Findings show that the presence of pain at the ankle can alter participants' proprioceptive threshold during gait. Clinical assessment of proprioception should therefore carefully consider the presence of pain when evaluating a patient's performance using clinical proprioceptive test and consider the negative effect of pain on proprioceptive threshold for test interpretation.

Altered activity of pain processing brain regions in association with hip osteoarthritis

Hip osteoarthritis (OA) is characterized by chronic pain, but there remains a mismatch between symptoms and radiological findings. Recently, brain connectivity has been implicated in the modulation of chronic peripheral pain, however its association with perceived pain in hip OA is not understood. We used resting-state functional magnetic resonance imaging (fMRI) to examine functional connectivity associated with pain in hip OA patients. Thirty participants with hip OA and 10 non-OA controls were recruited. Using the visual analogue scale (VAS), pain scores were obtained before and after performing a painful hip activity. All participants underwent 3.0 T resting-state fMRI, and functional connectivity of brain regions associated with pain was determined and compared between participants, and before and after hip activity. Relative to controls, functional connectivity between the secondary somatosensory cortex and left posterior insula was increased, and functional connectivity between the bilateral posterior insula and motor cortices was significantly decreased in hip OA participants. In response to painful hip activity, functional connectivity increased between the thalamus, periaqueductal grey matter and brainstem. Functional connections between brain regions associated with pain are altered in hip OA patients, and several connections are modulated by performing painful activity. Unique lateralization of left posterior insula and linked brain functional connectivity patterns allows assessment of pain perception in hip OA providing an unbiased method to evaluate pain perception and pain modulation strategies.

Functional MRI evidence for primary motor cortex plasticity contributes to the disease's severity and prognosis of cervical spondylotic myelopathy patients

OBJECTIVE

To investigate the brain mechanism of non-correspondence between diseases severity and compression degree of the spinal cord in cervical spondylotic myelopathy (CSM) patients and to test the utility of brain imaging biomarkers for predicting prognosis of CSM.

METHODS

We calculated voxel-wise zALFF from 54 CSM patients and 50 healthy controls using resting-state fMRI data. In analysis 1, we identified the brain regions exhibited significant differences of zALFF between CSM patients and healthy controls. In analyses 2 through 3, we investigated the zALFF differences between light-symptom CSM patients and severe-symptom CSM patients while carefully matching the degree of compression between these two groups. In analysis 4, we tested the utility of zALFF within the primary motor cortex (M1) for predicting the prognosis of CSM.

RESULTS

We found that (1) compared with the healthy controls, CSM patients exhibited higher ALFF within left M1, bilateral superior frontal gyrus, and lower zALFF within right precuneus and calcarine, suggesting altered brain neural activity in CSM patients; (2) after matching the compression degree, the CSM patients with more severe clinical symptoms exhibited higher zALFF within M1, indicating cortical function contributes to disease's severity of CSM; (3) taking the M1 zALFF as features in the prognosis prediction model improves the prediction accuracy, indicating that the M1 zALFF provide additional value for predicting the prognosis of CSM patients following decompression surgery.

CONCLUSION

The functional state of M1 contributes to the disease's severity of CSM and can provide complementary information for predicting the prognosis of CSM following decompression surgery.

KEY POINTS

• Cervical spondylotic myelopathy (CSM) patients exhibited increased zALFF within the primary motor cortex (M1), bilateral superior frontal gyrus, and decreased zALFF within the right precuneus and calcarine. • After matching the compression degree, the CSM patients with more severe clinical symptoms exhibited higher zALFF within M1, indicating cortical function contributes to disease severity of CSM. • zALFF within M1 provided additional value for predicting the prognosis of CSM patients.

Low Back Pain Assessment Based on Alpha Oscillation Changes in Spontaneous Electroencephalogram (EEG)

Objectively and accurately assessing pain in clinical settings is challenging. Previous studies showed that alpha oscillations of electroencephalogram data are correlated with subjective perceived pain. Based on this finding, this study is aimed at assessing chronic low back pain based on alpha oscillations. Multichannel electroencephalogram data were recorded from 27 subjects with chronic low back pain under the simple conditions of closing eyes or opening eyes. Spectral analyses were conducted to extract the alpha band responses, and the alpha powers were calculated for the two conditions, respectively. Normalized alpha power was calculated by subtracting the alpha power in the eyes-open condition from that in the eyes-closed condition. The correlation between the alpha power and the subjective pain intensity was evaluated in frontal, central, and posterior regions. The normalized alpha power in the central region was negatively correlated with the subjective pain intensity (R = -0.50, P = 0.01), with the strongest correlation occurring at the Cz electrode (R = -0.59, P = 0.04). The correlation analysis results demonstrated the possibility of using the differences of alpha spectral power between eyes-closed and eyes-open conditions as a measure for assessing chronic low back pain. The findings suggest that the normalized alpha power in the central region may be used as a measurable and quantitative indicator of chronic pain for clinical applications.

The Effect of Transcranial Direct Current Stimulation on Chronic Neuropathic Pain in Patients with Multiple Sclerosis: Randomized Controlled Trial

OBJECTIVE

Chronic neuropathic pain is a common symptom in multiple sclerosis (MS). This randomized controlled single-blinded study investigated whether a new protocol involving five days of transcranial direct current stimulation (tDCS) with an interval period would be effective to reduce pain using the visual analog scale (VAS). Other secondary outcomes included the Neuropathic Pain Scale (NPS), Depression Anxiety Stress Score (DASS), Short Form McGill Pain Questionnaire (SFMPQ), and Multiple Sclerosis Quality of Life 54 (MSQOL54).

DESIGN

A total of 30 participants were recruited for the study, with 15 participants randomized to a sham group or and 15 randomized to an active group. After a five-day course of a-tDCS, VAS and NPS scores were measured daily and then weekly after treatment up to four weeks after treatment. Secondary outcomes were measured pretreatment and then weekly up to four weeks.

RESULTS

After a five-day course of a-tDCS, VAS scores were significantly reduced compared with sham tDCS and remained significantly low up to week 2 post-treatment. There were no statistically significant mean changes in MSQOL54, SFMPQ, NPS, or DASS for the sham or treatment group before treatment or at four-week follow-up.

CONCLUSIONS

This study shows that repeated stimulation with a-tDCS for five days can reduce pain intensity for a prolonged period in patients with MS who have chronic neuropathic pain.

Disrupted Neural Activity in Individuals With Iridocyclitis Using Regional Homogeneity: A Resting-State Functional Magnetic Resonance Imaging Study

Objective: This study used the regional homogeneity (ReHo) technique to explore whether spontaneous brain activity is altered in patients with iridocyclitis.

Methods: Twenty-six patients with iridocyclitis (14 men and 12 women) and 26 healthy volunteers (15 men and 11 women) matched for sex and age were enrolled in this study. The ReHo technique was used to comprehensively assess changes in whole-brain synchronous neuronal activity. The diagnostic ability of the ReHo method was evaluated by means of receive operating characteristic (ROC) curve analysis. Moreover, associations of average ReHo values in different brain areas and clinical characteristics were analyzed using correlation analysis.

Result: Compared with healthy volunteers, reduced ReHo values were observed in patients with iridocyclitis in the following brain regions: the right inferior occipital gyrus, bilateral calcarine, right middle temporal gyrus, right postcentral gyrus, left superior occipital gyrus, and left precuneus. In contrast, ReHo values were significantly enhanced in the right cerebellum, left putamen, left supplementary motor area, and left inferior frontal gyrus in patients with iridocyclitis, compared with healthy volunteers (false discovery rate correction, P < 0.05).

Conclusion: Patients with iridocyclitis exhibited disturbed synchronous neural activities in specific brain areas, including the visual, motor, and somatosensory regions, as well as the default mode network. These findings offer a novel image-guided research strategy that might aid in exploration of neuropathological or compensatory mechanisms in patients with iridocyclitis.

Posterior insular activity contributes to the late laser-evoked potential component in EEG recordings

OBJECTIVE

Nociceptive activity in some brain areas has concordantly been reported in EEG source models, such as the anterior/mid-cingulate cortex and the parasylvian area. Whereas the posterior insula has been constantly reported to be active in intracortical and fMRI studies, non-invasive EEG and MEG recordings mostly failed to detect activity in this region. This study aimed to determine an appropriate inverse modeling approach in EEG recordings to model posterior insular activity, assuming the late LEP (laser evoked potential) time window to yield a better separation from other ongoing cortical activity.

METHODS

In 12 healthy volunteers, nociceptive stimuli of three intensities were applied. LEP were recorded using 32-channel EEG recordings. Source analysis was performed in specific time windows defined in the grand-average dataset. Two distinct dipole-pairs located close to the operculo-insular area were compared.

RESULTS

Our results show that posterior insular activity yields a substantial contribution to the latest part (positive component) of the LEP.

CONCLUSIONS

Even though the initial insular activity onset is in the early LEP time window,modelingthe insular activity in the late LEP time window might result in better separation from other ongoing cortical activity.

SIGNIFICANCE

Modeling the late LEP activity might enable to distinguish posterior insular activity.

Dynamics of neuronal oscillations underlying nociceptive response in the mouse primary somatosensory cortex

Pain is caused by tissue injury, inflammatory disease, pathogen invasion, or neuropathy. The perception of pain is attributed to the neuronal activity in the brain. However, the dynamics of neuronal activity underlying pain perception are not fully known. Herein, we examined theta-oscillation dynamics of local field potentials in the primary somatosensory cortex of a mouse model of formalin-induced pain, which usually shows a bimodal behavioral response interposed between pain-free periods. We found that formalin injection exerted a reversible shift in the theta-peak frequency toward a slower frequency. This shift was observed during nociceptive phases but not during the pain-free period and was inversely correlated with instantaneous pain intensity. Furthermore, instantaneous oscillatory analysis indicated that the probability of slow theta oscillations increased during nociceptive phases with an association of augmented slow theta power. Finally, cross-frequency coupling between theta and gamma oscillations indicated that the coupling peak frequency of theta oscillations was also shifted toward slower oscillations without affecting coupling strength or gamma power. Together, these results suggest that the dynamic changes in theta oscillations in the mouse primary somatosensory cortex represent the ongoing status of pain sensation.

Neural Correlates of Cognitive Dysfunctions in Cervical Spondylotic Myelopathy Patients: A Resting-State fMRI Study

Cervical spondylotic myelopathy (CSM) is a common disease of the elderly that is characterized by gait instability, sensorimotor deficits, etc. Recurrent symptoms including memory loss, poor attention, etc. have also been reported in recent studies. However, these have been rarely investigated in CSM patients. To investigate the cognitive deficits and their correlation with brain functional alterations, we conducted resting-state fMRI (rs-fMRI) signal variability. This is a novel indicator in the neuroimaging field for assessing the regional neural activity in CSM patients. Further, to explore the network changes in patients, functional connectivity (FC) and graph theory analyses were performed. Compared with the controls, the signal variabilities were significantly lower in the widespread brain regions especially at the default mode network (DMN), visual network, and somatosensory network. The altered inferior parietal lobule signal variability positively correlated with the cognitive function level. Moreover, the FC and the global efficiency of DMN increased in patients with CSM and positively correlated with the cognitive function level. According to the study results, (1) the cervical spondylotic myelopathy patients exhibited regional neural impairments, which correlated with the severity of cognitive deficits in the DMN brain regions, and (2) the increased FC and global efficiency of DMN can compensate for the regional impairment.

New Developments in Non-invasive Brain Stimulation in Chronic Pain

Purpose of Review

The goal of this review is to present a summary of the recent literature of a non-invasive brain stimulation (NIBS) to alleviate pain in people with chronic pain syndromes. This article reviews the current evidence for the use of transcranial direct current (tDCS) and repetitive transcranial magnetic stimulation (rTMS) to improve outcomes in chronic pain. Finally, we introduce the reader to novel stimulation methods that may improve therapeutic outcomes in chronic pain.

Recent Findings

While tDCS is approved for treatment of fibromyalgia in Canada and the European Union, no NIBS method is currently approved for chronic pain in the United States. Increasing sample sizes in randomized clinical trials (RCTs) seems the most efficient way to increase confidence in initial promising results. Trends at funding agencies reveal increased interest and support for NIBS such as recent Requests for Application from the National Institutes of Health. NIBS in conjunction with cognitive behavioral therapy and physical therapy may enhance outcomes in chronic pain. Novel stimulation methods, such as transcranial ultrasound stimulation, await rigorous study in chronic pain.

Early gamma-oscillations as correlate of localized nociceptive processing in primary sensorimotor cortex

Recent studies put forward the idea that stimulus-evoked gamma-band oscillations (GBOs; 30-100 Hz) play a specific role in nociception. So far, evidence for the specificity of GBOs for nociception, their possible involvement in nociceptive sensory discriminatory abilities, and knowledge regarding their cortical sources is just starting to grow. To address these questions, we used electroencephalography (EEG) to record brain activity evoked by phasic nociceptive laser stimuli and tactile stimuli applied at different intensities to the right hand and foot of 12 healthy volunteers. The EEG was analyzed in the time domain to extract phase-locked event-related brain potentials (ERPs) and in three regions of interest in the time-frequency domain (delta/theta, 40-Hz gamma, 70-Hz gamma) to extract stimulus-evoked changes in the magnitude of non-phase-locked brain oscillations. Both nociceptive and tactile stimuli, matched with respect to subjective intensity, elicited phase locked ERPs of increasing amplitude with increasing stimulus intensity. In contrast, only nociceptive stimuli elicited a significant enhancement of GBOs (65-85 Hz, 150-230 ms after stimulus onset), whose magnitude encoded stimulus intensity, whereas tactile stimuli led to a GBO decrease. Following nociceptive hand stimulation, the topographical distribution of GBOs was maximal at contralateral electrode C3, whereas maximum activity following foot stimulation was recorded at the midline electrode Cz, compatible with generation of GBOs in the representations of the hand and foot of the primary sensorimotor cortex, respectively. The differential behavior of high-frequency GBOs and low-frequency 40-Hz GBOs is indicating different functional roles and regions in sensory processing.NEW & NOTEWORTHY Gamma-band oscillations show hand-foot somatotopy compatible with generation in primary sensorimotor cortex and are present following nociceptive but not tactile stimulation of the hand and foot in humans.

Moderate to severe acute pain disturbs motor cortex intracortical inhibition and facilitation in orthopedic trauma patients: A TMS study

OBJECTIVE

Primary motor (M1) cortical excitability alterations are involved in the development and maintenance of chronic pain. Less is known about M1-cortical excitability implications in the acute phase of an orthopedic trauma. This study aims to assess acute M1-cortical excitability in patients with an isolated upper limb fracture (IULF) in relation to pain intensity.

METHODS

Eighty-four (56 IULF patients <14 days post-trauma and 28 healthy controls). IULF patients were divided into two subgroups according to pain intensity (mild versus moderate to severe pain). A single transcranial magnetic stimulation (TMS) session was performed over M1 to compare groups on resting motor threshold (rMT), short-intracortical inhibition (SICI), intracortical facilitation (ICF), and long-interval cortical inhibition (LICI).

RESULTS

Reduced SICI and ICF were found in IULF patients with moderate to severe pain, whereas mild pain was not associated with M1 alterations. Age, sex, and time since the accident had no influence on TMS measures.

DISCUSSION

These findings show altered M1 in the context of acute moderate to severe pain, suggesting early signs of altered GABAergic inhibitory and glutamatergic facilitatory activities.

Strengthened Hippocampal Circuits Underlie Enhanced Retrieval of Extinguished Fear Memories Following Mindfulness Training

BACKGROUND

The role of hippocampus in context-dependent recall of extinction is well recognized. However, little is known about how intervention-induced changes in hippocampal networks relate to improvements in extinction learning. In this study, we hypothesized that mindfulness training creates an optimal exposure condition by heightening attention and awareness of present moment sensory experience, leading to enhanced extinction learning, improved emotion regulation, and reduced anxiety symptoms.

METHODS

We tested this hypothesis in a randomized controlled longitudinal study design using a 2-day fear conditioning and extinction protocol. The mindfulness training group included 42 participants (28 women) and the control group included 25 participants (15 women).

RESULTS

We show that mindfulness training is associated with differential engagement of the right supramarginal gyrus as well as hippocampal-cortical reorganization. We also report enhanced hippocampal connectivity to the primary sensory cortex during retrieval of extinguished stimuli following mindfulness training.

CONCLUSIONS

These findings suggest hippocampal-dependent changes in contextual retrieval as one plausible neural mechanism through which mindfulness-based interventions enhance fear extinction and foster stress resilience.

The "virtual lesion" approach to transcranial magnetic stimulation: studying the brain-behavioral relationships in experimental pain

Transcranial magnetic stimulation (TMS) can be used to create a temporary “virtual lesion” (VL) of a target cortical area, disrupting its function and associated behavior. Transcranial magnetic stimulation can therefore test the functional role of specific brain areas. This scoping review aims at investigating the current literature of the “online” TMS-evoked VL approach to studying brain–behavioral relationships during experimental pain in healthy subjects. Ovid-Medline, Embase, and Web of Science electronic databases were searched. Included studies tested different TMS-based VLs of various pain brain areas during continuous experimental pain or when time-locked to a noxious stimulus. Outcome measures assessed different pain measurements. Initial screening resulted in a total of 403 studies, of which 17 studies were included in the review. The VLs were directed to the prefrontal, primary and secondary somatosensory, primary motor, and parietal cortices through single/double/triple/sequence of five-TMS pulses or through repeated TMS during mechanical, electrical contact, radiant heat, or capsaicin-evoked noxious stimulation. Despite a wide variability among the VL protocols, outcome measures, and study designs, a behavioral VL effect (decrease or increase in pain responses) was achieved in the majority of the studies. However, such findings on the relationships between the modified brain activity and the manifested pain characteristics were often mixed. To conclude, TMS–elicited VLs during experimental pain empower our understanding of brain–behavior relationships at specific time points during pain processing. The mixed findings of these relationships call for an obligatory standard of all pain-related TMS protocols for clearly determining the magnitude and direction of TMS-induced behavioral effects.

Effects of continuous theta-burst stimulation of the primary motor and secondary somatosensory areas on the central processing and the perception of trigeminal nociceptive input in healthy volunteers

Supplemental Digital Content is Available in the Text.

Inactivating paired continuous theta-burst stimulation of the primary motor cortex but not on the secondary somatosensory area flattened the relationship between brain activation and stimulus strength while not impacting on the subjective perceptions.

Noninvasive modulation of the activity of pain-related brain regions by means of transcranial magnetic stimulation promises an innovative approach at analgesic treatments. However, heterogeneous successes in pain modulation by setting reversible “virtual lesions” at different brain areas point at unresolved problems including the optimum stimulation site. The secondary somatosensory cortex (S2) has been previously identified to be involved in the perception of pain-intensity differences. Therefore, impeding its activity should impede the coding of the sensory component of pain intensity, resulting in a flattening of the relationship between pain intensity and physical stimulus strength. This was assessed using inactivating spaced continuous theta-burst stimulation (cTBS) in 18 healthy volunteers. In addition, cTBS was applied on the primary motor cortex (M1) shown previously to yield moderate and variable analgesic effects, whereas sham stimulation at both sites served as placebo condition. Continuous theta-burst stimulation flattened the relationship between brain activation and stimulus strength, mainly at S2, the insular cortex, and the postcentral gyrus (16 subjects analyzed). However, these effects were observed after inactivation of M1 while this effect was not observed after inactivation of S2. Nevertheless, both the M1 and the S2-spaced cTBS treatment were not reflected in the ratings of the nociceptive stimuli of different strengths (17 subjects analyzed), contrasting with the clear coding of stimulus strength by these data. Hence, while modulating the central processing of nociceptive input, cTBS failed to produce subjectively relevant changes in pain perception, indicating that the method in the present implementation is still unsuitable for clinical application.

Suppression of Somatosensory Evoked Cortical Responses by Noxious Stimuli

Paired-pulse suppression refers to attenuation of neural activity in response to a second stimulus and has a pivotal role in inhibition of redundant sensory inputs. Previous studies have suggested that cortical responses to a somatosensory stimulus are modulated not only by a preceding same stimulus, but also by stimulus from a different submodality. Using magnetoencephalography, we examined somatosensory suppression induced by three different conditioning stimuli. The test stimulus was a train of electrical pulses to the dorsum of the left hand at 100 Hz lasting 1500 ms. For the pulse train, the intensity of the stimulus was abruptly increased at 1200 ms. Cortical responses to the abrupt intensity change were recorded and used as the test response. Conditioning stimuli were presented at 600 ms as pure tones, either innocuous or noxious electrical stimulation to the right foot. Four stimulus conditions were used: (1) Test alone, (2) Test + auditory stimulus, (3) Test + somatosensory stimulus, and (4) Test + nociceptive stimulus. Our results showed that the amplitude of the test response was significantly smaller for conditions (3) and (4) in the secondary somatosensory cortex contralateral (cSII) and ipsilateral (iSII) to the stimulated side as compared to the response to condition (1), whereas the amplitude of the response in the primary somatosensory cortex did not differ among the conditions. The auditory stimulus did not have effects on somatosensory change-related response. These findings show that somatosensory suppression was induced by not only a conditioning stimulus of the same somatosensory submodality and the same cutaneous site to the test stimulus, but also by that of a different submodality in a remote area.

Clinical neurophysiology of pain

Clinical neurophysiologic investigation of pain pathways in humans is based on specific techniques and approaches, since conventional methods of nerve conduction studies and somatosensory evoked potentials do not explore these pathways. The proposed techniques use various types of painful stimuli (thermal, laser, mechanical, or electrical) and various types of assessments (measurement of sensory thresholds, study of nerve fiber excitability, or recording of electromyographic reflexes or cortical potentials). The two main tests used in clinical practice are quantitative sensory testing and pain-related evoked potentials (PREPs). In particular, PREPs offer the possibility of an objective assessment of nociceptive pathways. Three types of PREPs can be distinguished depending on the type of stimulation used to evoke pain: laser-evoked potentials, contact heat evoked potentials, and intraepidermal electrical stimulation evoked potentials (IEEPs). These three techniques investigate both small-diameter peripheral nociceptive afferents (mainly Aδ nerve fibers) and spinothalamic tracts without theoretically being able to differentiate the level of lesion in the case of abnormal results. In routine clinical practice, PREP recording is a reliable method of investigation for objectifying the existence of a peripheral or central lesion or loss of function concerning the nociceptive pathways, but not the existence of pain. Other methods, such as nerve fiber excitability studies using microneurography, more directly reflect the activities of nociceptive axons in response to provoked pain, but without detecting or quantifying the presence of spontaneous pain. These methods are more often used in research or experimental study design. Thus, it should be kept in mind that most of the results of neurophysiologic investigation performed in clinical practice assess small fiber or spinothalamic tract lesions rather than the neuronal mechanisms directly at the origin of pain and they do not provide objective quantification of pain.

Altered intrinsic brain activity in patients with toothaches using the amplitude of low-frequency fluctuations: a resting-state fMRI study

BACKGROUND

The results of previous studies have indicated that pain-associated diseases can result in marked functional and anatomical alterations in the brain. However, differences in spontaneous brain activity occurring in toothache (TA) patients remain unclear.

OBJECTIVE

This study investigated intrinsic brain activity changes in TA subjects using the amplitude of low-frequency fluctuation (ALFF) technique.

METHODS

A total of 18 patients with TA (eight males, and 10 females) and 18 healthy controls (HCs) who were matched for gender, age, and educational status were enrolled. Resting-state functional MRI was used to examine the participants. Spontaneous cerebral activity variations were investigated using the ALFF technique. The mean ALFF values of the TA patients and the HCs were classified using receiver operating characteristic (ROC) curves. The correlations between ALFF signals of distinct regions of the cerebrum and the clinical manifestations of the TA patients were evaluated using Pearson's correlation analysis.

RESULTS

Compared with HCs, TA patients showed notably higher ALFF in the left postcentral gyrus, right paracentral lobule, right lingual gyrus, right inferior occipital gyrus, left fusiform gyrus, and right superior occipital gyrus. ROC curve analysis of each brain region showed that the accuracy area under the curve was excellent. In the TA group, the visual analog scale of the left side was positively correlated with the ALFF signal values of the right paracentral lobule (r=0.639, P=0.025).

CONCLUSION

Multiple brain regions, including pain- and vision-related areas, exhibited aberrant intrinsic brain activity patterns, which may help to explain the underlying neural mechanisms in TA.

Characterizing the Short-Term Habituation of Event-Related Evoked Potentials

Fast-rising sensory events evoke a series of functionally heterogeneous event-related potentials (ERPs). Stimulus repetition at 1 Hz induces a strong habituation of the largest ERP responses, the vertex waves (VWs). VWs are elicited by stimuli regardless of their modality, provided that they are salient and behaviorally relevant. In contrast, the effect of stimulus repetition on the earlier sensory components of ERPs has been less explored, and the few existing results are inconsistent. To characterize how the different ERP waves habituate over time, we recorded the responses elicited by 60 identical somatosensory stimuli (activating either non-nociceptive Aβ or nociceptive Aδ afferents), delivered at 1 Hz to healthy human participants. We show that the well-described spatiotemporal sequence of lateralized and vertex ERP components elicited by the first stimulus of the series is largely preserved in the smaller-amplitude, habituated response elicited by the last stimuli of the series. We also found that the earlier lateralized sensory wave habituates across the 60 trials following the same decay function of the VWs: this decay function is characterized by a large drop at the first stimulus repetition followed by smaller decreases at subsequent repetitions. Interestingly, the same decay functions described the habituation of ERPs elicited by repeated non-nociceptive and nociceptive stimuli. This study provides a neurophysiological characterization of the effect of prolonged and repeated stimulation on the main components of somatosensory ERPs. It also demonstrates that both lateralized waves and VWs are obligatory components of ERPs elicited by non-nociceptive and nociceptive stimuli.

The increased release of amino acid neurotransmitters of the primary somatosensory cortical area in rats contributes to remifentanil-induced hyperalgesia and its inhibition by lidocaine

Background

Studies have confirmed that activation of the neurons of primary somatosensory cortex (S1) is involved in the process of remifentanil (Remi)-induced hyperalgesia (RIH), which can be suppressed by lidocaine (Lido). A total intravenous anesthesia model of rats mimicking clinical Remi-based anesthesia was set up to explore the release of amino acid neurotransmitters of S1 cortex in RIH and its inhibition by Lido in this study.

Materials and methods

Sprague Dawley rats were randomly divided into the following four groups: propofol (Pro), Remi, Remi combined Lido, and Lido groups. Mechanical hyperalgesia was evaluated by von Frey test; the amino acid neurotransmitters in the microdialysates of S1 area were detected by high-performance liquid chromatography (HPLC)-fluorescence, and conventional protein kinase C (cPKC)γ levels in the whole-cell lysates and membrane lipid rafts (MLRs) were determined by Western blotting.

Results

The von Frey test showed that co-administration of Lido significantly inhibited a Remi-induced decrease in the threshold of the paw withdrawal response in Remi group at 2 h postinfusion. Meanwhile, the Remi-induced increases in both the excitatory and inhibitory amino acid releases in S1 were suppressed by co-administrating Lido within 5 h postinfusion. Western blotting showed that the increased cPKCγ level in the membrane lipid rafts (MLR) induced by Remi was also inhibited by Lido.

Conclusion

The increased release of amino acid neurotransmitters and the translocation of cPKCγ in MLR suggest the activation of S1 neurons, which may be one of the mechanisms underlying RIH. Lido reduces the release of amino acid neurotransmitters in S1 neurons and the translocation of cPKCγ in MLRs after stopping Remi, which may be one of its antihyperalgesic mechanisms.

Designing Brains for Pain: Human to Mollusc

There is compelling evidence that the "what it feels like" subjective experience of sensory stimuli arises in the cerebral cortex in both humans as well as mammalian experimental animal models. Humans are alone in their ability to verbally communicate their experience of the external environment. In other species, sensory awareness is extrapolated on the basis of behavioral indicators. For instance, cephalopods have been claimed to be sentient on the basis of their complex behavior and anecdotal reports of human-like intelligence. We have interrogated the findings of avoidance learning behavioral paradigms and classical brain lesion studies and conclude that there is no evidence for cephalopods feeling pain. This analysis highlighted the questionable nature of anthropometric assumptions about sensory experience with increased phylogenetic distance from humans. We contend that understanding whether invertebrates such as molluscs are sentient should first begin with defining the computational processes and neural circuitries underpinning subjective awareness. Using fundamental design principles, we advance the notion that subjective awareness is dependent on observer neural networks (networks that in some sense introspect the neural processing generating neural representations of sensory stimuli). This introspective process allows the observer network to create an internal model that predicts the neural processing taking place in the network being surveyed. Predictions arising from the internal model form the basis of a rudimentary form of awareness. We develop an algorithm built on parallel observer networks that generates multiple levels of sensory awareness. A network of cortical regions in the human brain has the appropriate functional properties and neural interconnectivity that is consistent with the predicted circuitry of the algorithm generating pain awareness. By contrast, the cephalopod brain lacks the necessary neural circuitry to implement such an algorithm. In conclusion, we find no compelling behavioral, functional, or neuroanatomical evidence to indicate that cephalopods feel pain.

Assessment of synchronous neural activities revealed by regional homogeneity in individuals with acute eye pain: a resting-state functional magnetic resonance imaging study

Objective

Previous neuroimaging studies have demonstrated that pain-related diseases are associated with brain function and anatomical abnormalities, whereas altered synchronous neural activity in acute eye pain (EP) patients has not been investigated. The purpose of this study was to explore whether or not synchronous neural activity changes were measured with the regional homogeneity (ReHo) method in acute EP patients.

Methods

A total of 20 patients (15 males and 5 females) with EP and 20 healthy controls (HCs) consisting of 15 and 5 age-, sex-, and education-matched males and females, respectively, underwent resting-state functional magnetic resonance imaging. The ReHo method was applied to assess synchronous neural activity changes.

Results

Compared with HCs, acute EP patients had significantly lower ReHo values in the left precentral/postcentral gyrus (Brodmann area [BA]3/4), right precentral/postcentral gyrus (BA3/4), and left middle frontal gyrus (BA6). In contrast, higher ReHo values in acute EP patients were observed in the left superior frontal gyrus (BA11), right inferior parietal lobule (BA39/40), and left precuneus (BA7). However, no relationship was found between the mean ReHo signal values of the different areas and clinical manifestations, which included both the duration and degree of pain in EP patients.

Conclusion

Our study highlighted that acute EP patients showed altered synchronous neural activities in many brain regions, including somatosensory regions. These findings might provide useful information for exploration of the neural mechanisms underlying acute EP.

Can a single pulse transcranial magnetic stimulation targeted to the motor cortex interrupt pain processing?

The modulatory role of the primary motor cortex (M1), reflected by an inhibitory effect of M1-stimulation on clinical pain, motivated us to deepen our understanding of M1’s role in pain modulation. We used Transcranial Magnetic Stimulation (TMS)-induced virtual lesion (VL) to interrupt with M1 activity during noxious heat pain. We hypothesized that TMS-VL will effect experimental pain ratings. Three VL protocols were applied consisting of single-pulse TMS to transiently interfere with right M1 activity: (1) VL_M1- TMS applied to 11 subjects, 20 msec before the individual’s first pain-related M1 peak activation, as determined by source analysis (sLORETA), (2) VL_-50 (N = 16; TMS applied 50 ms prior to noxious stimulus onset), and (3) VL₊₁₅₀ (N = 16; TMS applied 150 ms after noxious stimulus onset). Each protocol included 3 conditions ('pain-alone', ' TMS-VL', and ‘SHAM-VL’), each consisted of 30 noxious heat stimuli. Pain ratings were compared, in each protocol, for TMS-VL vs. SHAM-VL and vs. pain-alone conditions. Repeated measures analysis of variance, corrected for multiple comparisons revealed no significant differences in the pain ratings between the different conditions within each protocol. Therefore, our results from this exploratory study suggest that a single pulse TMS-induced VL that is targeted to M1 failed to interrupt experimental pain processing in the specific three stimulation timing examined here.

Advancing Transcranial Magnetic Stimulation Methods for Complex Regional Pain Syndrome: An Open-Label Study of Paired Theta Burst and High-Frequency Stimulation

INTRODUCTION

Complex Regional Pain Syndrome (CRPS), a rare and severe chronic pain condition, often responds poorly to existing treatments. Previous studies demonstrated Transcranial Magnetic Stimulation (TMS) provided short-term pain relief for upper extremity CRPS.

METHODS

Building on previous methodologies, we employed a TMS protocol that may lead to significant pain relief for upper and lower extremity CRPS in a nonrandomized open label pilot trial involving 21 participants. We individualized TMS coil positioning over motor cortex of somatic pain location, and administered intermittent theta-burst stimulation followed by 10 Hz high-frequency stimulation using a deeper targeting coil. We assessed response (≥30% pain reduction) from a single session (n = 5) and five consecutive daily sessions (n = 12) and compared change in pain from baseline, after one treatment and one-week posttreatment between groups using a mixed ANVOA.

RESULTS

Both groups demonstrated significant pain reduction after one session and one-week posttreatment; however, no group differences were present. From a single session, 60% of participants responded at Week 1. From five sessions, 58% and 50% of participants responded at Weeks 1 and 2, respectively. Two from each group achieved >50% pain reduction beyond six to eight weeks. No serious adverse events occurred. Though headache and nausea were the most common side-effects, we urge careful monitoring to prevent seizures with this protocol.

CONCLUSIONS

We used a TMS protocol that, for the first time, led to significant pain relief in upper and lower extremity CRPS, and will soon examine our protocol in a larger, controlled trial.

Pain syndromes and the parietal lobe

Pain was considered to be integrated subcortically during most of the 20^th century, and it was not until 1956 that focal injury to the parietal opercular-insular cortex was shown to produce selective loss of pain senses. The parietal operculum and adjacent posterior insula are the main recipients of spinothalamic afferents in primates. The innermost operculum appears functionally associated with the posterior insula and can be segregated histologically, somatotopically and neurochemically from the more lateral S2 areas. The Posterior Insula and Medial Operculum (PIMO) encompass functional networks essential to initiate cortical nociceptive processing. Destruction of this region selectively abates pain sensations; direct stimulation generates acute pain, and epileptic foci trigger painful seizures. Lesions of the PIMO have also high potential to develop central pain with dissociated loss of pain and temperature. The PIMO region behaves as a somatosensory area on its own, which handles phylogenetically old somesthetic capabilities based on thinly myelinated or unmyelinated inputs. It integrates spinothalamic-driven information - not only nociceptive but also innocuous heat and cold, crude touch, itch, and possibly viscero-somatic interoception. Conversely, proprioception, graphesthesia or stereognosis are not processed in this area but in S1 cortices. Given its anatomo-functional properties, thalamic connections, and tight relations with limbic and multisensory cortices, the region comprising the inner parietal operculum and posterior insula appears to contain a third somatosensory cortex contributing to the spinothalamic attributes of the final perceptual experience.

Evidence-based source modeling of nociceptive cortical responses: A direct comparison of scalp and intracranial activity in humans

BACKGROUND

Source modeling of EEG traditionally relies on interplay between physiological hypotheses and mathematical estimates. We propose to optimize the process by using evidence gathered from brain imaging and intracortical recordings.

METHODS

We recorded laser-evoked potentials in 18 healthy participants, using high-density EEG. Brain sources were modeled during the first second poststimulus, constraining their initial position to regions where nociceptive-related activity has been ascertained by intracranial EEG. These comprised the two posterior operculo-insular regions, primary sensorimotor, posterior parietal, anterior cingulate/supplementary motor (ACC/SMA), bilateral frontal/anterior insular, and posterior cingulate (PCC) cortices.

RESULTS

The model yielded an average goodness of fit of 91% for individual and 95.8% for grand-average data. When compared with intracranial recordings from 27 human subjects, no significant difference in peak latencies was observed between modeled and intracranial data for 5 of the 6 assessable regions. Morphological match was excellent for operculo-insular, frontal, ACC/SMA and PCC regions (cross-correlation > 0.7) and fair for sensori-motor and posterior parietal cortex (c-c ∼ 0.5).

CONCLUSIONS

Multiple overlapping activities evoked by nociceptive input can be disentangled from high-density scalp EEG guided by intracranial data. Modeled sources accurately described the timing and morphology of most activities recorded with intracranial electrodes, including those coinciding with the emergence of stimulus awareness. Hum Brain Mapp 38:6083-6095, 2017. © 2017 Wiley Periodicals, Inc.

High-resolution functional MRI identified distinct global intrinsic functional networks of nociceptive posterior insula and S2 regions in squirrel monkey brain

Numerous functional imaging and electrophysiological studies in humans and animals indicate that the two contiguous areas of secondary somatosensory cortex (S2) and posterior insula (pIns) are core regions in nociceptive processing and pain perception. In this study, we tested the hypothesis that the S2-pIns connection serves as a hub for connecting distinct sensory and affective nociceptive processing networks in the squirrel monkey brain. At 9.4T, we first mapped the brain regions that respond to nociceptive heat stimuli with high-resolution fMRI, and then used seed-based resting-state fMRI (rsfMRI) analysis to delineate and refine the global intrinsic functional connectivity circuits of the proximal S2 and pIns regions. In each subject, nociceptive (47.5°C) heat-evoked fMRI activations were detected in many brain regions, including primary somatosensory (S1), S2, pIns, area 7b, anterior cingulate cortex (ACC), primary motor cortex, prefrontal cortex, supplementary motor area, thalamus, and caudate. Using the heat-evoked fMRI activation foci in S2 and pIns as the seeds, voxel-wise whole-brain resting-state functional connectivity (rsFC) analysis revealed strong functional connections between contralateral S2 and pIns, as well as their corresponding regions in the ipsilateral hemisphere. Spatial similarity and overlap analysis identified each region as part of two distinct intrinsic functional networks with 7% overlap: sensory S2-S1-area 7b and affective pIns-ACC-PCC networks. Moreover, a high degree of overlap was observed between the combined rsFC maps of nociceptive S2 and pIns regions and the nociceptive heat-evoked activation map. In summary, our study provides evidence for the existence of two distinct intrinsic functional networks for S2 and pIns nociceptive regions, and these two networks are joined via the S2-pIns connection. Brain regions that are involved in processing nociceptive inputs are also highly interconnected at rest. The presence of robust and distinct S1-S2-area 7b and pIns-ACC-PCC rsFC networks under anesthesia underscores their fundamental roles in processing nociceptive information.

The relationship of corticospinal excitability with pain, motor performance and disability in subjects with chronic wrist/hand pain

There is a growing body of evidence of changes in corticospinal excitability associated with musculoskeletal disorders, however there is a lack of knowledge of how these changes relate to measures of pain, motor performance and disability. An exploratory study was performed utilizing Transcranial Magnetic Stimulation to investigate differences in corticospinal excitability in the Abductor Pollicis Brevis (APB) between 15 pain-free subjects and 15 subjects with chronic wrist/hand pain and to determine how corticospinal excitability was associated with measures of pain (visual analog scale, AUSCAN™), hand motor performance (isometric and key pinch strength, Purdue Pegboard Test), disability (AUSCAN™), and spinal motoneuronal excitability. Input-output curves demonstrated increased corticospinal excitability of the APB in the affected hand of subjects with chronic pain (p<0.01). Changes in corticospinal excitability were significantly correlated with pain intensity (r=0.77), disability (r=0.58), and negatively correlated with motoneuronal excitability (r=-0.57). Corticospinal excitability in subjects with heterogeneous injuries of the wrist/hand was associated with disability and pain.

Localized N20 Component of Somatosensory Evoked Magnetic Fields in Frontoparietal Brain Tumor Patients Using Noise-Normalized Approaches

PURPOSE

To localize sensorimotor cortical activation in 10 patients with frontoparietal tumors using quantitative magnetoencephalography (MEG) with noise-normalized approaches.

MATERIAL AND METHODS

Somatosensory evoked magnetic fields (SEFs) were elicited in 10 patients with somatosensory tumors and in 10 control participants using electrical stimulation of the median nerve via the right and left wrists. We localized the N20m component of the SEFs using dynamic statistical parametric mapping (dSPM) and standardized low-resolution brain electromagnetic tomography (sLORETA) combined with 3D magnetic resonance imaging (MRI). The obtained coordinates were compared between groups. Finally, we statistically evaluated the N20m parameters across hemispheres using non-parametric statistical tests.

RESULTS

The N20m sources were accurately localized to Brodmann area 3b in all members of the control group and in seven of the patients; however, the sources were shifted in three patients relative to locations outside the primary somatosensory cortex (SI). Compared with the affected (tumor) hemispheres in the patient group, N20m amplitudes and the strengths of the current sources were significantly lower in the unaffected hemispheres and in both hemispheres of the control group. These results were consistent for both dSPM and sLORETA approaches.

CONCLUSION

Tumors in the sensorimotor cortex lead to cortical functional reorganization and an increase in N20m amplitude and current-source strengths. Noise-normalized approaches for MEG analysis that are integrated with MRI show accurate and reliable localization of sensorimotor function.