Altered functional connectivity of the periaqueductal gray in chronic neck and shoulder pain

Investigating the brain functional abnormalities underlying pain hypervigilance in chronic neck and shoulder pain: a resting-state fMRI study

PURPOSE

To investigate pain hypervigilance in individuals suffering from chronic neck and shoulder pain (CNSP) and its underlying brain mechanism.

METHODS

The evaluation of pain vigilance was conducted through the utilization of pain vigilance and awareness questionnaires. Voxel-wise regional homogeneity (ReHo) from 60 CNSP patients and 60 healthy controls (HCs) using resting-state fMRI data. Voxel-wise two-sample T-test was conducted to reveal the ReHo variations between CNSP and HC. Correlation analyses were utilized to reveal the connection between brain abnormalities and medical measurements. Furthermore, a mediation analysis was conducted to elucidate the pathway-linking changes in brain function with medical measurements.

RESULTS

Our present study revealed three main findings. Firstly, patients with CSNP demonstrated a heightened vigilance of pain in comparison to healthy adults, a common occurrence among individuals with chronic pain conditions. Secondly, we observed brain abnormalities in various brain regions in CSNP patients, and these alterations were associated with the extent of pain vigilance. Lastly, the pain hypervigilance impact on the severity of pain was found to be controlled by regional neural activity in the anterior cingulate cortex (ACC) in subjects with CSNP.

CONCLUSION

Our findings suggested that long-term repetitive nociceptive input caused by chronic pain further aggravates the pain intensity by impairing the vigilance-related pain processing within the anterior cingulate cortex in CNSP patients.

Electroacupuncture Attenuates Neuropathic Pain in a Rat Model of Cervical Spondylotic Radiculopathy: Involvement of Spinal Cord Synaptic Plasticity

Purpose

Cervical spondylotic radiculopathy (CSR) is a common neurologic condition that causes chronic neck pain and motor functions, with neuropathic pain (NP) being the primary symptom. Although it has been established that electroacupuncture (EA) can yield an analgesic effect in clinics and synaptic plasticity plays a critical role in the development and maintenance of NP, the underlying mechanisms have not been fully elucidated. In this study, we explored the potential mechanisms underlying EA's effect on synaptic plasticity in CSR rat models.

Materials and Methods

The CSR rat model was established by spinal cord compression (SCC). Electroacupuncture stimulation was applied to LI4 (Hegu) and LR3 (Taichong) acupoints for 20 min once a day for 7 days. Pressure pain threshold (PPT) and mechanical pain threshold (MPT) were utilized to detect the pain response of rats. A gait score was used to evaluate the motor function of rats. Enzyme-linked immunosorbent assay (ELISA), Western blot (WB), immunohistochemistry (IHC), immunofluorescence (IF), and transmission electron microscopy (TEM) were performed to investigate the effects of EA.

Results

Our results showed that EA alleviated SCC-induced spontaneous pain and gait disturbance. ELISA showed that EA could decrease the concentration of pain mediators in the cervical nerve root. WB, IHC, and IF results showed that EA could downregulate the expression of synaptic proteins in spinal cord tissues and promote synaptic plasticity. TEM revealed that the EA could reverse the synaptic ultrastructural changes induced by CSR.

Conclusion

Our findings reveal that EA can inhibit SCC-induced NP by modulating the synaptic plasticity in the spinal cord and provide the foothold for the clinical treatment of CSR with EA.

Clinical Application of Evoked Potentials in the Operation of Cervical Spondylotic Myelopathy with Different Imaging

Objective

To observe the effects of improvement of cervical spondylotic myelopathy with different imaging signals after cortical somatosensory-evoked potentials on the functional recovery of postoperative patients and the effect of surgery.

Methods

A total of 60 patients with cervical spondylotic myelopathy who were hospitalized in our hospital from January 2020 to December 2020 were selected and divided into a case group (30 cases) with MRI-indicated changes in intramedullary signals and a control group (30 cases) with MRI-indicated spinal cord changes. Intragroup and intergroup control studies were conducted through general observation indexes, neurological evaluation indexes, imaging, and evoked potential observation indexes. Somatosensory-evoked potentials were performed before operation, 1 week after operation, and 24 weeks after operation, and the JOA score of each patient was obtained before operation, 1 week after operation, and 24 weeks after operation.

Results

The JOA score of 1 week after operation of the case group is (16.25 ± 1.54) and the control group is (11.89 ± 1.63), and there is a statistically significant difference (P < 0.05). The JOA score of the case group 24 weeks after operation is (25.27 ± 1.03) and the control group is (13.28 ± 1.03), and the difference is statistically significant (P < 0.05). The improvement rate of 1 week after operation and 24 weeks after operation was statistically significant between the two groups (P < 0.05). The case group improvement rate is (70.5 ± 8.72)% and the control group is (40.5 ± 9.81)%, and the difference is statistically significant between the two groups (P < 0.05).

Conclusion

The preoperative intramedullary signal changes can be used as an effective index for patients with cervical spondylotic myelopathy to use somatosensory-evoked potentials to assess the prognosis of patients after surgery.

Neurophysiology of hypnosis in chronic pain: A review of recent literature

Chronic pain is a complex phenomenon which includes biological, psychological, and socio-professional factors that undermine patients' everyday life. Currently, only few patients significantly benefit from pharmacological treatments and many have to stop them because of negative side effects. Moreover, no medication or treatment addresses all aspects of chronic pain at once (i.e., sensations, emotions, behaviors, and cognitions), positioning chronic pain as an important public health issue and thus contributing to high health-care costs. Consequently, patients and health-care providers are increasingly turning to complementary non-pharmacological techniques such as hypnosis. Clinical research has demonstrated a decrease of pain perception, pain interference, depression and anxiety, and an increase in global quality of life when patients with chronic pain have benefited from hypnosis learning. Neuroimaging studies offer a possible explanation of these results by focusing on neural processes of pain modulation in chronic pain patients' brain. Studies conducted with chronic pain patients showed a modulation of pain matrix activity during hypnosis with a specific involvement of the anterior cingulate cortex (related to emotional and cognitive processing of pain). Therefore, hypnosis seems to act upon regions underlying emotion and cognition, with an influence on pain perception and emotional regulation. In this review, we propose to carry out a review of the recent literature on hypnosis in chronic pain management. A better understanding of the beneficial effects of hypnosis on chronic pain and its neurophysiology should enable more systematic use of this technique in the management of this complex health problem.

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.

Abnormal connectivity model of raphe nuclei with sensory-associated cortex in Parkinson's disease with chronic pain

BACKGROUND AND OBJECTIVE

There are indicates that raphe nuclei may be involved in the occurrence of chronic pain in Parkinson's disease (PD). In the study, we investigated the functional connectivity pattern of raphe nuclei in Parkinson's disease with chronic pain (PDP) to uncover its possible pathophysiology.

METHODS

Fifteen PDP, who suffered from pain, lasted longer than 3 months, sixteen Parkinson's disease patients with no pain (nPDP) and eighteen matched normal health controls (NCs) were recruited. All subjects completed the King's Parkinson's Pain Scale (KPPS) besides Parkinson-related scale and demographics. We performed a seed-based resting-state analysis of functional magnetic resonance imaging to explore whole-brain functional connectivity of the raphe nuclei. Multiple regression model was used to explore the related factors of pain including disease duration, disease severity, Hamilton Depression Rating Scale, age, sex, levodopa equivalent dose and the strength of network functional connectivity.

RESULTS

Compared with the nPDP, the PDP group showed stronger functional connectivity between raphe nuclei and pain-related brain regions, including parietal lobe, insular lobe, cingulum cortex and prefrontal cortex, and the functional connectivity values of those areas were significantly positively correlated with KPPS independent of the clinical variables. Compared with NCs, the combined PD groups showed decreased functional connectivity including prefrontal cortex and cingulum cortex.

CONCLUSIONS

Abnormal functional connectivity model of raphe nuclei may be partly involved in pathophysiological mechanism of pain in PD.

Modulation effect of acupuncture treatment on chronic neck and shoulder pain in female patients: Evidence from periaqueductal gray-based functional connectivity

Aims

Chronic neck and shoulder pain (CNSP) is a common neurological disorder, which females are more likely to suffer from. The periaqueductal gray (PAG) plays a key role in the descending modulation of pain. This study aimed to investigate altered PAG‐based functional connectivity (FC) in female patients with CNSP related to healthy controls (HCs) and the effect of acupuncture for female patients with CNSP using PAG‐based FC biomarkers.

Methods

PAG‐based FC value was calculated based on resting‐state functional images and then compared between patients with CNSP at pre‐acupuncture, post‐acupuncture, and HCs. Then, correlational analyses were performed to examine the relationships between increased PAG‐based FC strength and improved clinical parameters in patients after acupuncture treatment.

Results

Before acupuncture treatment, compared to HCs, patients with CSNP showed altered PAG‐based FC with widely distributed brain regions, including the left medial superior frontal gyrus, bilateral posterior insula (pIns), and cingulate gyrus. After treatment, patients with CNSP exhibited specially improved PAG‐pIns FC compared to that before treatment, and no significant difference was observed in the increased PAG‐pIns FC strength between HCs and patients with CNSP after treatment. Furthermore, pain catastrophizing reduction was significantly correlated with the increased PAG‐pIns FC strength in patients after treatment.

Conclusion

The effect of acupuncture treatment may relate to the increased PAG‐pIns FC, which significantly correlated with pain catastrophizing reduction after treatment. These findings shed important mechanistic information on the role of therapeutic approaches in treating chronic neck and shoulder pain.

Machine learning approaches applied in spinal pain research

The purpose of this narrative review is to provide a critical reflection of how analytical machine learning approaches could provide the platform to harness variability of patient presentation to enhance clinical prediction. The review includes a summary of current knowledge on the physiological adaptations present in people with spinal pain. We discuss how contemporary evidence highlights the importance of not relying on single features when characterizing patients given the variability of physiological adaptations present in people with spinal pain. The advantages and disadvantages of current analytical strategies in contemporary basic science and epidemiological research are reviewed and we consider how analytical machine learning approaches could provide the platform to harness the variability of patient presentations to enhance clinical prediction of pain persistence or recurrence. We propose that machine learning techniques can be leveraged to translate a potentially heterogeneous set of variables into clinically useful information with the potential to enhance patient management.

Different modulation effects of 1 Hz and 20 Hz transcutaneous auricular vagus nerve stimulation on the functional connectivity of the periaqueductal gray in patients with migraine

Background

A growing body of evidence suggests that transcutaneous auricular vagus nerve stimulation (taVNS) may relieve symptoms of migraineurs. Frequency is one of the key stimulation parameters. The aim of this study is to investigate the modulation effect of taVNS frequency on the descending pain modulation system (DPMS) in patients with migraine.

Methods

Twenty-four episodic migraineurs without aura (21 females) were recruited for the single-blind, crossover, functional magnetic resonance imaging (fMRI) study. Each participant attended two separate fMRI scan sessions, one for 1 Hz and another for 20 Hz taVNS, in a random order. Seed-based functional connectivity analysis was applied using the ventrolateral periaqueductal gray (PAG) as the region of interest.

Results

Compared with the pre-taVNS resting state, continuous 1 Hz taVNS (during) produced a significant increase in functional connectivity between the PAG and the bilateral middle cingulate cortex (MCC), right precuneus, left middle frontal gyrus (MFG), and left cuneus. Compared with 20 Hz taVNS, 1 Hz taVNS produced greater PAG connectivity increases with the MCC, right precuneus/posterior cingulate cortex, left insula, and anterior cingulate cortex (ACC). A significant negative correlation was observed between the number of migraine attacks in the previous 4 weeks and the PAG-MCC functional connectivity in the pre-taVNS resting-state before 1 Hz taVNS.

Conclusions

Our findings suggest that taVNS with different frequencies may produce different modulation effects on the descending pain modulation system, demonstrating the important role of stimulation frequency in taVNS treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03024-9.

Acupuncture Treatment Modulates the Connectivity of Key Regions of the Descending Pain Modulation and Reward Systems in Patients with Chronic Low Back Pain

Chronic low back pain (cLBP) is a common disorder with unsatisfactory treatment options. Acupuncture has emerged as a promising method for treating cLBP. However, the mechanism underlying acupuncture remains unclear. In this study, we investigated the modulation effects of acupuncture on resting state functional connectivity (rsFC) of the periaqueductal gray (PAG) and ventral tegmental area (VTA) in patients with cLBP. Seventy-nine cLBP patients were recruited and assigned to four weeks of real or sham acupuncture. Resting state functional magnetic resonance imaging data were collected before the first and after the last treatment. Fifty patients completed the study. We found remission of pain bothersomeness in all treatment groups after four weeks, with greater pain relief after real acupuncture compared to sham acupuncture. We also found that real acupuncture can increase VTA/PAG rsFC with the amygdala, and the increased rsFC was associated with decreased pain bothersomeness scores. Baseline PAG-amygdala rsFC could predict four-week treatment response. Our results suggest that acupuncture may simultaneously modulate the rsFC of key regions in the descending pain modulation (PAG) and reward systems (VTA), and the amygdala may be a key node linking the two systems to produce antinociceptive effects. Our findings highlight the potential of acupuncture for chronic low back pain management.

Altered intrinsic brain activity and regional cerebral blood flow in patients with chronic neck and shoulder pain

Purpose

To identify the changes of intrinsic brain activity and regional cerebral blood flow in patients with chronic neck and shoulder pain (CNSP) by using amplitude of low-frequency fluctuation (ALFF) analysis and arterial spin labelling study.

Material and methods

In total, 28 CNSP patients and 25 age-matched and sex-matched healthy controls (HCs) participated in the study. Resting-state functional magnetic resonance imaging (rs-fMRI) and arterial spin labelling (ASL) MRI were acquired. Correlations between ALFF and cerebral blood flow (CBF) were analysed. Subsequently, the differences in ALFF and CBF were compared in the two groups. Finally, the visual analogue scale (VAS) was also assessed in the CNSP group.

Results

Compared with HCs, CNSP patients showed significantly abnormal ALFF and CBF in several brain regions, including the cerebellum posterior lobe, middle orbitofrontal gyrus, medial superior frontal gyrus, middle temporal gyrus, precuneus, cingulate gyrus, middle occipital gyrus, middle frontal gyrus, postcentral gyrus, precentral gyrus, and superior parietal gyrus. Correlation analysis showed that the ALFF value of the medial superior frontal gyrus positively correlated with the VAS score. However, no correlation was found between the CBF values and the VAS score.

Conclusions

The altered ALFF and CBF values in CNSP patients were observed in different pain-related brain regions that were involved in pain modulation and perception. The combination of rs-fMRI and ASL MRI might provide complementary information for increasing our understanding of the neuropathology in CNSP.

MicroRNA-204 silencing relieves pain of cervical spondylotic radiculopathy by targeting GDNF

Cervical spondylosis may cause chronic neck pain, radiculopathy and/or myelopathy, and consequently results in severe brain damage. Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for motoneurons. Accumulating microRNAs (miRNAs) have highlighted as critical regulators of GDNF signaling in the mediation of neuroinflammation and neuropathic pain. Hence, we performed this study to investigate the potential role of miR-204 in the neuropathic pain of cervical spondylotic radiculopathy (CSR) by targeting GDNF. A rat model of spinal cord compression (SCC) was established to stimulate a pathologic lesion. RT-qPCR and western blot assays characterized the downregulation of GDNF and the upregulation of miR-204 in spinal cord tissues of rats under the conditions of SCC. Moreover, miR-204 could directly target GDNF, as evidenced by dual-luciferase reporter gene assay. In order to elucidate the roles of miR-204 and GDNF in SCC-induced neuropathic pain, miR-204 sponge, GDNF, or shRNA against GDNF was introduced to the rats, followed by measurements for SCC-induced neuroinflammation and neuropathic pain. GDNF upregulation or miR-204 silencing was identified to reduce the spontaneous pain score, gait scores and cell apoptosis. Furthermore, GDNF upregulation or miR-204 silencing resulted in elevated amplitude of sensory-evoked potentials (SEPs), number of motoneurons, release of pro-inflammatory factors, TNF-α, and IL-1β in addition to an increase in the anti-inflammatory factor BDNF. Taken together, upregulation of GDNF induced by miR-204 silencing confers protection against SCC-induced pain in rat models, suggesting a potential therapeutic target for CSR treatment.

Modulatory effects of different exercise modalities on the functional connectivity of the periaqueductal grey and ventral tegmental area in patients with knee osteoarthritis: a randomised multimodal magnetic resonance imaging study

BACKGROUND

Knee osteoarthritis is a prevalent disorder with unsatisfactory treatment options. Both physical and mindful exercises may be able to relieve its pain symptoms. We compared the modulatory effects of different exercise modalities on the periaqueductal grey (PAG) and ventral tegmental area (VTA), which play important roles in descending opioidergic pathways and reward/motivation systems in patients with knee osteoarthritis.

METHODS

We recruited and randomised 140 patients into Tai Chi, Baduanjin, stationary cycling, and health education control groups for 12 weeks. Knee injury and Osteoarthritis Outcome Score (KOOS), functional and structural MRI, and blood biomarkers were measured at the beginning and end of the experiment. We used the PAG and VTA as seeds in resting-state functional connectivity (rsFC) analysis.

RESULTS

Compared with the control group: (i) all exercises significantly increased KOOS pain sub-scores (pain reduction) and serum programmed death 1 (PD-1) concentrations; (ii) all exercises decreased right PAG rsFC with the medial orbital prefrontal cortex, and the decreased rsFC was associated with improvements in knee pain; and (iii) grey matter volume in the medial orbital prefrontal cortex was significantly increased in all exercise groups. There was also significantly decreased rsFC between the left VTA and the medial orbital prefrontal cortex in the Tai Chi and Baduanjin groups.

CONCLUSIONS

Exercise can simultaneously modulate the rsFC of the descending opioidergic pathway and reward/motivation system and blood inflammation markers. Elucidating the shared and unique mechanisms of different exercise modalities may facilitate the development of exercise-based interventions for chronic pain.

CLINICAL TRIAL REGISTRATION

ChiCTR-IOR-16009308.

Periaqueductal gray and emotions: the complexity of the problem and the light at the end of the tunnel, the magnetic resonance imaging

The periaqueductal gray (PAG) is less referred in relationship with emotions than other parts of the brain (e.g. cortex, thalamus, amygdala), most probably because of the difficulty to reach and manipulate this small and deeply lying structure. After defining how to evaluate emotions, we have reviewed the literature and summarized data of the PAG contribution to the feeling of emotions focusing on the behavioral and neurochemical considerations. In humans, emotions can be characterized by three main domains: the physiological changes, the communicative expressions, and the subjective experiences. In animals, the physiological changes can mainly be studied. Indeed, early studies have considered the PAG as an important center of the emotions-related autonomic and motoric processes. However, in vivo imaging have changed our view by highlighting the PAG as a significant player in emotions-related cognitive processes. The PAG lies on the crossroad of networks important in the regulation of emotions and therefore it should not be neglected. In vivo imaging represents a good tool for studying this structure in living organism and may reveal new information about its role beyond its importance in the neurovegetative regulation.

Different mechanisms of contralateral- or ipsilateral-acupuncture to modulate the brain activity in patients with unilateral chronic shoulder pain: a pilot fMRI study

Background

Chronic shoulder pain (CSP) is a common disease causing pain and functional limitation, which is highly prevalent and has substantial negative effects on the quality of life. Acupuncture has gained popularity and has been accepted gradually by many countries because it can successfully treat patients with chronic pain, but the specific brain mechanisms under acupuncture treatment for CSP remain unclear. Therefore, in this study, we aimed to 1) compare the clinical effects between acupuncture at the contralateral and ipsilateral Tiaokou (ST 38) point in patients with unilateral shoulder pain and 2) explore how contralateral- and ipsilateral-acupuncture modulates the regional homogeneity (ReHo) of patients with CSP.

Patients and methods

This was a pilot functional magnetic resonance imaging (fMRI) trial. Twenty-four patients with CSP were recruited and randomized to the contralateral acupuncture group (contra-group) and the ipsilateral acupuncture group (ipsi-group). All patients completed resting-state functional magnetic resonance imaging (fMRI) scans before and after acupuncture treatment. Shoulder pain intensity (visual analog scale [VAS]) and shoulder joint function (Constant–Murley score [CMS]) were used to evaluate clinical efficiency of treatment. ReHo was used to assess resting-state brain activity.

Results

We found clinical improvement in decreasing pain intensity and increasing shoulder function in both groups, and the mean objective shoulder functional improvement in contra-group was better than that in ipsi-group (p = 0.010). Interestingly, the brain mechanism of contra-acupuncture at ST 38 was distinguishable from ipsi-acupuncture regarding ReHo values.

Conclusion

Anterior cingulate cortex (ACC) may play a direct role in the regulation of brain by the contralateral acupuncture at ST 38 in patients with shoulder pain. On the contrary, the pathway of brainstem-thalamus-cortex may be likely to work in mechanism of acupuncture at ipsilateral ST 38.

Significance

Our results indicate that the clinical effects and brain mechanisms are different between the stimulation given at contralateral and ipsilateral acupoints in patients with CSP and imply that the selection of either contralateral or ipsilateral acupuncture therapy to treat some chronic pain conditions is necessary.

Responsivity of Periaqueductal Gray Connectivity Is Related to Headache Frequency in Episodic Migraine

Migraineurs show hypersensitivity to sensory stimuli at various stages throughout the migraine cycle. A number of putative processes have been implicated including a dysfunction in the descending pain modulatory system in which the periaqueductal gray (PAG) is considered to play a crucial role. Recurring migraine attacks could progressively perturb this system, lowering the threshold for future attacks, and contribute to disease chronification. Here, we investigated PAG connectivity with other brain regions during a noxious thermal stimulus to determine changes in migraineurs, and associations with migraine frequency. 21 episodic migraine patients and 22 matched controls were included in the study. During functional MRI, a thermode was placed on the subjects' temple delivering noxious and non-noxious heat stimuli. A psychophysiological interaction (PPI) analysis was carried out to examine pain-induced connectivity of the PAG with other brain regions. The PPI analysis showed increased PAG connectivity with the S1 face representation area and the supplementary motor area, an area involved with pain expectancy, in patients with higher frequency of migraine attacks. PAG connectivity with regions involved with the descending pain modulatory system (i.e., prefrontal cortex) was decreased in the migraineurs versus healthy individuals. Our results suggest that high frequency migraineurs may have diminished resistance to cephalic pain and a less efficient inhibitory pain modulatory response to external stressor (i.e., noxious heat). The findings support the notion that in migraine there is less effective pain modulation (viz., decreased pain inhibition or increased pain facilitation), potentially contributing to increased occurrence of attacks/chronification of migraine.