Thickening in the somatosensory cortex of patients with migraine

Neural Plasticity in Common Forms of Chronic Headaches

Headaches are universal experiences and among the most common disorders. While headache may be physiological in the acute setting, it can become a pathological and persistent condition. The mechanisms underlying the transition from episodic to chronic pain have been the subject of intense study. Using physiological and imaging methods, researchers have identified a number of different forms of neural plasticity associated with migraine and other headaches, including peripheral and central sensitization, and alterations in the endogenous mechanisms of pain modulation. While these changes have been proposed to contribute to headache and pain chronification, some findings are likely the results of repetitive noxious stimulation, such as atrophy of brain areas involved in pain perception and modulation. In this review, we provide a narrative overview of recent advances on the neuroimaging, electrophysiological and genetic aspects of neural plasticity associated with the most common forms of chronic headaches, including migraine, cluster headache, tension-type headache, and medication overuse headache.

Catecholaminergic Gene Polymorphisms Are Associated with GI Symptoms and Morphological Brain Changes in Irritable Bowel Syndrome

BACKGROUND

Genetic and environmental factors contribute to the pathophysiology of irritable bowel syndrome (IBS). In particular, early adverse life events (EALs) and the catecholaminergic system have been implicated.

AIMS

To investigate whether catecholaminergic SNPs with or without interacting with EALs are associated with: 1) a diagnosis of IBS, 2) IBS symptoms and 3) morphological alterations in brain regions associated with somatosensory, viscerosensory, and interoceptive processes.

METHODS

In 277 IBS and 382 healthy control subjects (HCs), 11 SNPs in genes of the catecholaminergic signaling pathway were genotyped. A subset (121 IBS, 209 HCs) underwent structural brain imaging (magnetic resonance imaging [MRI]). Logistic and linear regressions evaluated each SNP separately and their interactions with EALs in predicting IBS and GI symptom severity, respectively. General linear models determined grey matter (GM) alterations from the SNPs and EALs that were predictive of IBS.

RESULTS

1) DIAGNOSIS: There were no statistically significant associations between the SNPs and IBS status with or without the interaction with EAL after adjusting for multiple comparisons. 2) SYMPTOMS: GI symptom severity was associated with ADRA1D rs1556832 (P = 0.010). 3) Brain morphometry: In IBS, the homozygous genotype of the major ADRA1D allele was associated with GM increases in somatosensory regions (FDR q = 0.022), left precentral gyrus (q = 0.045), and right hippocampus (q = 0.009). In individuals with increasing sexual abuse scores, the ADRAβ2 SNP was associated with GM changes in the left posterior insula (q = 0.004) and left putamen volume (q = 0.029).

CONCLUSION

In IBS, catecholaminergic SNPs are associated with symptom severity and morphological changes in brain regions concerned with sensory processing and modulation and affect regulation. Thus, certain adrenergic receptor genes may facilitate or worsen IBS symptoms.

Motor cortex stimulation and neuropathic pain: how does motor cortex stimulation affect pain-signaling pathways?

OBJECTIVE

Neuropathic pain is often severe. Motor cortex stimulation (MCS) is used for alleviating neuropathic pain, but the mechanism of action is still unclear. This study aimed to understand the mechanism of action of MCS by investigating pain-signaling pathways, with the expectation that MCS would regulate both descending and ascending pathways.

METHODS

Neuropathic pain was induced in Sprague-Dawley rats. Surface electrodes for MCS were implanted in the rats. Tactile allodynia was measured by behavioral testing to determine the effect of MCS. For the pathway study, immunohistochemistry was performed to investigate changes in c-fos and serotonin expression; micro-positron emission tomography (mPET) scanning was performed to investigate changes of glucose uptake; and extracellular electrophysiological recordings were performed to demonstrate brain activity.

RESULTS

MCS was found to modulate c-fos and serotonin expression. In the mPET study, altered brain activity was observed in the striatum, thalamic area, and cerebellum. In the electrophysiological study, neuronal activity was increased by mechanical stimulation and suppressed by MCS. After elimination of artifacts, neuronal activity was demonstrated in the ventral posterolateral nucleus (VPL) during electrical stimulation. This neuronal activity was effectively suppressed by MCS.

CONCLUSIONS

This study demonstrated that MCS effectively attenuated neuropathic pain. MCS modulated ascending and descending pain pathways. It regulated neuropathic pain by affecting the striatum, periaqueductal gray, cerebellum, and thalamic area, which are thought to regulate the descending pathway. MCS also appeared to suppress activation of the VPL, which is part of the ascending pathway.

Gray matter correlates of migraine and gender effect: A meta-analysis of voxel-based morphometry studies

BACKGROUND

An increasing number of neuroimaging studies have revealed gray matter (GM) anomalies of several brain regions by voxel-based morphometry (VBM) studies in migraineurs. However, not all the studies reported entirely consistent findings. Our aim is to investigate concurrence across VBM studies to help clarify the structural anomalies underpinning this condition.

METHODS

A systematic search of VBM studies of patients with migraine and healthy controls (HC) published in PubMed and Embase databases from January 2000 to March 2014 was conducted. A quantitative meta-analysis of whole-brain VBM studies in patients with migraine compared with HC was performed by means of anisotropic effect size version of signed differential mapping (AES-SDM) software package.

RESULTS

Nine studies comprising 222 patients with migraine and 230 HC subjects were included in the present study. Compared to HC subjects, the patients group showed consistent decreased GM in the posterior insular-opercular regions, the prefrontal cortex, and the anterior cingulate cortex. Results remained largely unchanged in the following jackknife sensitivity analyses. Meta-regression analysis showed that a higher percentage of females in the patient sample was associated with decreased GM in the right dorsolateral prefrontal cortex.

CONCLUSIONS

This is the first quantitative whole-brain VBM meta-analysis in migraine showing strong evidence of brain GM anomalies within the pain-processing neural network. Further longitudinal investigations are needed to determine whether these structural anomalies are reversible with effective treatment on migraine.

Neuroimaging of chronic pain

Chronic pain is an important public health problem, and there is a need to understand the mechanisms that lead to pain chronification. From a neurobiological perspective, the mechanisms contributing to the transition from acute to subacute and chronic pain are heterogeneous and are thought to take place at various levels of the peripheral and central nervous system. In the past decade, brain imaging studies have shed light on neural correlates of pain perception and pain modulation, but they have also begun to disentangle neural mechanisms that underlie chronic pain. This review summarizes important and recent findings in pain research using magnetic resonance tomography. Especially new developments in functional, structural and neurochemical imaging such as resting-state connectivity and γ-aminobutyric acid (GABA) spectroscopy, which have advanced our understanding of chronic pain and which can potentially be integrated in clinical practice, will be discussed.

Migraine: multiple processes, complex pathophysiology

Migraine is a common, multifactorial, disabling, recurrent, hereditary neurovascular headache disorder. It usually strikes sufferers a few times per year in childhood and then progresses to a few times per week in adulthood, particularly in females. Attacks often begin with warning signs (prodromes) and aura (transient focal neurological symptoms) whose origin is thought to involve the hypothalamus, brainstem, and cortex. Once the headache develops, it typically throbs, intensifies with an increase in intracranial pressure, and presents itself in association with nausea, vomiting, and abnormal sensitivity to light, noise, and smell. It can also be accompanied by abnormal skin sensitivity (allodynia) and muscle tenderness. Collectively, the symptoms that accompany migraine from the prodromal stage through the headache phase suggest that multiple neuronal systems function abnormally. As a consequence of the disease itself or its genetic underpinnings, the migraine brain is altered structurally and functionally. These molecular, anatomical, and functional abnormalities provide a neuronal substrate for an extreme sensitivity to fluctuations in homeostasis, a decreased ability to adapt, and the recurrence of headache. Advances in understanding the genetic predisposition to migraine, and the discovery of multiple susceptible gene variants (many of which encode proteins that participate in the regulation of glutamate neurotransmission and proper formation of synaptic plasticity) define the most compelling hypothesis for the generalized neuronal hyperexcitability and the anatomical alterations seen in the migraine brain. Regarding the headache pain itself, attempts to understand its unique qualities point to activation of the trigeminovascular pathway as a prerequisite for explaining why the pain is restricted to the head, often affecting the periorbital area and the eye, and intensifies when intracranial pressure increases.

Cortical spreading depolarization stimulates gliogenesis in the rat entorhinal cortex

Recently, we showed that cortical spreading depolarizations (CSDs) are a potent trigger of hippocampal neurogenesis. Here, we evaluated CSD-induced cytogenesis in the entorhinal cortex (EC), which provides the major afferent input to the dentate gyrus. Cortical spreading depolarizations were induced by epidural application of 3 mol/L KCl, controls received equimolar NaCl. Cytogenesis was analyzed at different time points thereafter by means of intraperitoneal 5-bromodeoxyuridine injections (day 2, 4, or days 1 to 7) and immunohistochemistry. Recurrent CSD significantly increased numbers of newborn cells in the ipsilateral EC. The majority of these cells expressed glial markers. Microglia proliferation was maximal at day 2, whereas NG2 glia and astrocytes responded for a prolonged period of time (days 2 to 4). Newborn glia remained detectable for 6 weeks after CSD. Whereas we furthermore detected newborn cells immunopositive for doublecortin, a marker for immature neuronal cells, we found no evidence for the generation of new neurons in the EC. Our results indicate that CSD is a potent gliogenic stimulus, leading to rapid and enduring changes in the glial cellular composition of the affected brain tissue. Thus, CSD facilitates ongoing structural remodeling of the directly affected cortex that might contribute to the pathophysiology of CSD-related brain pathologies.

Cortical hot spots and labyrinths: why cortical neuromodulation for episodic migraine with aura should be personalized

Stimulation protocols for medical devices should be rationally designed. For episodic migraine with aura we outline model-based design strategies toward preventive and acute therapies using stereotactic cortical neuromodulation. To this end, we regard a localized spreading depression (SD) wave segment as a central element in migraine pathophysiology. To describe nucleation and propagation features of the SD wave segment, we define the new concepts of cortical hot spots and labyrinths, respectively. In particular, we firstly focus exclusively on curvature-induced dynamical properties by studying a generic reaction-diffusion model of SD on the folded cortical surface. This surface is described with increasing level of details, including finally personalized simulations using patient's magnetic resonance imaging (MRI) scanner readings. At this stage, the only relevant factor that can modulate nucleation and propagation paths is the Gaussian curvature, which has the advantage of being rather readily accessible by MRI. We conclude with discussing further anatomical factors, such as areal, laminar, and cellular heterogeneity, that in addition to and in relation to Gaussian curvature determine the generalized concept of cortical hot spots and labyrinths as target structures for neuromodulation. Our numerical simulations suggest that these target structures are like fingerprints, they are individual features of each migraine sufferer. The goal in the future will be to provide individualized neural tissue simulations. These simulations should predict the clinical data and therefore can also serve as a test bed for exploring stereotactic cortical neuromodulation.

Temporal lobe cortical thickness correlations differentiate the migraine brain from the healthy brain

Background

Interregional cortical thickness correlations reflect underlying brain structural connectivity and functional connectivity. A few prior studies have shown that migraine is associated with atypical cortical brain structure and atypical functional connectivity amongst cortical regions that participate in sensory processing. However, the specific brain regions that most accurately differentiate the migraine brain from the healthy brain have yet to be determined. The aim of this study was to identify the brain regions that comprised interregional cortical thickness correlations that most differed between migraineurs and healthy controls.

Methods

This was a cross-sectional brain magnetic resonance imaging (MRI) investigation of 64 adults with migraine and 39 healthy control subjects recruited from tertiary-care medical centers and their surrounding communities. All subjects underwent structural brain MRI imaging on a 3T scanner. Cortical thickness was determined for 70 brain regions that cover the cerebral cortex and cortical thickness correlations amongst these regions were calculated. Cortical thickness correlations that best differentiated groups of six migraineurs from controls and vice versa were identified.

Results

A model containing 15 interregional cortical thickness correlations differentiated groups of migraineurs from healthy controls with high accuracy. The right temporal pole was involved in 13 of the 15 interregional correlations while the right middle temporal cortex was involved in the other two.

Conclusions

A model consisting of 15 interregional cortical thickness correlations accurately differentiates the brains of small groups of migraineurs from those of healthy controls. Correlations with the right temporal pole were highly represented in this classifier, suggesting that this region plays an important role in migraine pathophysiology.

Migraine and the Mu-opioidergic system-Can we directly modulate it? Evidence from neuroimaging studies

Migraine is a chronic trigeminal pain condition that affects the daily lives of a large part of our population. Its debilitating headache attacks, with increased sensitivity to multiple forms of stimuli, force many patients to rely on over the counter analgesics and resort to abuse of prescription medications, particularly opioid agonists. In the latter case, the indiscriminate medication-driven activation of the opioid system can lead to undesired side effects, such as the augmentation of hyperalgesia and allodynia, as well as the chronification of the attacks. However, we still lack information regarding the impact of migraine attacks and their relief on the function of μ-opioid receptor (μOR) mediated neurotransmission, the primary target of opioid medications. This line of inquiry is of particular importance as this neurotransmitter system is arguably the brain's most important endogenous mechanism involved in pain regulation, and understanding this endogenous mechanism is crucial in determining the effectiveness of opioid medications. Recently, new advances in molecular neuroimaging and neuromodulation have provided important information that can elucidate, in vivo, the role of the endogenous opioid system in migraine suffering and relief.

The neuromodulation of neuropathic pain by measuring pain response rate and pain response duration in animal

Objective

Neuropathic pain causes patients feel indescribable pain. Deep Brain Stimulation (DBS) is one of the treatment methods in neuropathic pain but the action mechanism is still unclear. To study the effect and mechanism of analgesic effects from DBS in neuropathic pain and to enhance the analgesic effect of DBS, we stimulated the ventral posterolateral nucleus (VPL) in rats.

Methods

To observe the effect from VPL stimulation, we established 3 groups : normal group (Normal group), neuropathic pain group (Pain group) and neuropathic pain+DBS group (DBS group). Rats in DBS group subjected to electrical stimulation and the target is VPL.

Results

We observed the behavioral changes by DBS in VPL (VPL-DBS) on neuropathic pain rats. In our study, the pain score which is by conventional test method was effectively decreased. In specific, the time of showing withdrawal response from painful stimulation which is not used measuring method in our animal model was also decreased by DBS.

Conclusion

The VPL is an effective target on pain modulation. Specifically we could demonstrate changes of pain response duration which is not used, and it was also significantly meaningful. We thought that this study would be helpful in understanding the relation between VPL-DBS and neuropathic pain.

Altered Brain Structure and Function Correlate with Disease Severity and Pain Catastrophizing in Migraine Patients

To investigate the neuroanatomical and functional brain changes in migraine patients relative to healthy controls, we used a combined analytical approach including voxel- and surface-based morphometry along with resting-state functional connectivity to determine whether areas showing structural alterations in patients also showed abnormal functional connectivity. Additionally, we wanted to assess whether these structural and functional changes were associated with group differences in pain catastrophizing and migraine-related disease variables in patients. We acquired T1-weighted anatomical and functional magnetic resonance imaging scans during rest in human subjects with a diagnosis of migraine and healthy controls. Structural analyses revealed greater left hippocampal gray matter volume and reduced cortical thickness in the left anterior midcingulate in patients compared with controls. We also observed negative associations between pain catastrophizing and migraine disease variables and gray matter in areas implicated in processing the sensory, affective, and cognitive aspects of pain in patients. Functional connectivity analyses showed that migraine patients displayed disrupted connectivity between default mode, salience, cognitive, visuospatial, and sensorimotor networks, which was associated with group differences in pain catastrophizing and migraine-related disease variables in patients. Together, our findings show widespread morphological and functional brain abnormalities in migraineurs in affective, cognitive, visual, and pain-related brain areas, which are associated with increased pain catastrophizing, disease chronicity, and severity of symptoms, suggesting that these structural and functional changes may be a consequence of repeated, long-term nociceptive signaling leading to increased pain sensitivity, mood disturbances, and maladaptive coping strategies to deal with unrelenting pain.

Features of migraine aura in teenagers

BACKGROUND

Complex migraine aura in teenagers can be complicated to diagnose. The aim of this study was to present detailed features of migraine aura in teenage migraineurs.

METHODS

This cross-sectional study was conducted in the period from 2008 till 2013. A total number of 40 teenage migraineurs (20 females and 20 males) met criteria for this study. The patients were interviewed using a specially designed questionnaire for collecting data about migraine aura features. Main outcome measures were frequency of visual, somatosensory and higher cortical dysfunction (HCD) symptoms in teenage migraineurs population during the aura, and also within each individual.

RESULTS

Visual aura was reported in every attack, followed by somatosensory (60%) and dysphasic (36.4%) aura. Scintillating scotoma and blurry vision were mostly reported and predominant visual symptoms. The most common somatosensory symptom was numbness in hand. HCD were reported by 22 (55%) patients. Slowed speech was mostly reported symptom of HCD, followed by dyslexia, déjà vu phenomenon, color dysgnosia, and dyspraxia. In patients with HCD, aura frequency per year (6.18 ± 3.17 vs. 3.33 ± 2.03, p = 0.003) and prevalence of somatosensory symptoms (77.3% vs. 38.9%, p = 0.014) were significantly higher than in patients without HCD.

CONCLUSIONS

Aura symptoms vary to a great extent in complexity in teenage migraineurs. Consequently, results obtained in this study provide useful information for clinicians when faced with unusual migraine aura.

Evidence for brain morphometric changes during the migraine cycle: a magnetic resonance-based morphometry study

Neurophysiological investigations have demonstrated that there are unique fluctuations in the migraine brain functional activity between the ictal and interictal periods. Here we investigated the possibility that there are fluctuations over time also in whole brain morphometry of patients affected by episodic migraine without aura (MO).Twenty-four patients with untreated MO underwent 3T MRI scans during (n = 10) or between attacks (n = 14) and were compared to a group of 15 healthy volunteers (HVs). We then performed voxel-based-morphometry (VBM) analysis of structural T1-weighted MRI scans to determine if changes in brain structure were observed over the course of the migraine cycle.Interictally, MO patients had a significantly lower gray matter (GM) density within the right inferior parietal lobule, right temporal inferior gyrus, right superior temporal gyrus, and left temporal pole than did HVs. Ictally, GM density increased within the left temporal pole, bilateral insula, and right lenticular nuclei, but no areas exhibited decreased GM density.These morphometric GM changes between ictal and interictal phases suggest that abnormal structural plasticity may be an important mechanism of migraine pathology. Given the functional neuroanatomy of these areas, our findings suggest that migraine is a condition associated with global dysfunction of multisensory integration and memory processing.

Migraine and reward system-or is it aversive?

Migraine is a debilitating neurological disorder with grave consequences for both the individual and society. This review will focus on recent literature investigating how brain structures implicated in reward and aversion contribute to the genesis of migraine pain. There exist many overlapping and interacting brain regions within pain and reward circuitry that contribute to negative affect and subjective experience of pain. The emotional component of pain has been argued to be a greater metric of quality of life than its sensory component, and thus understanding the processes that influence this pain characteristic is essential to developing novel treatment strategies for mitigating migraine pain. We emphasize and provide evidence that abnormalities within the mesolimbic cortical reward pathways contribute to migraine pain and that there are structural and functional neuroplasticity within the overlapping brain regions common to both pain and reward.

The role of the blood-brain barrier in the development and treatment of migraine and other pain disorders

The function of the blood-brain barrier (BBB) related to chronic pain has been explored for its classical role in regulating the transcellular and paracellular transport, thus controlling the flow of drugs that act at the central nervous system, such as opioid analgesics (e.g., morphine) and non-steroidal anti-inflammatory drugs. Nonetheless, recent studies have raised the possibility that changes in the BBB permeability might be associated with chronic pain. For instance, changes in the relative amounts of occludin isoforms, resulting in significant increases in the BBB permeability, have been demonstrated after inflammatory hyperalgesia. Furthermore, inflammatory pain produces structural changes in the P-glycoprotein, the major efflux transporter at the BBB. One possible explanation for these findings is the action of substances typically released at the site of peripheral injuries that could lead to changes in the brain endothelial permeability, including substance P, calcitonin gene-related peptide, and interleukin-1 beta. Interestingly, inflammatory pain also results in microglial activation, which potentiates the BBB damage. In fact, astrocytes and microglia play a critical role in maintaining the BBB integrity and the activation of those cells is considered a key mechanism underlying chronic pain. Despite the recent advances in the understanding of BBB function in pain development as well as its interference in the efficacy of analgesic drugs, there remain unknowns regarding the molecular mechanisms involved in this process. In this review, we explore the connection between the BBB as well as the blood-spinal cord barrier and blood-nerve barrier, and pain, focusing on cellular and molecular mechanisms of BBB permeabilization induced by inflammatory or neuropathic pain and migraine.

Cortical spreading depression: origins and paths as inferred from the sequence of events during migraine aura

Patients with migraine with aura often experience a variety of visual and somatosensory phenomena and disturbances of higher cortical functions. Analysis of these alterations may provide important information about the involvement of different cortical regions in cortical spreading depression (CSD). We report five cases of migraineurs who experience unusually abundant clinical phenomena during auras. These patients were selected from a cohort of migraine with aura patients who were interviewed, using a specially designed questionnaire, to evaluate the presence of higher cortical dysfunctions. On the basis of the aura symptoms they reported, we attempted to infer the origin and the possible paths of CSD in each patient. According to their reported symptoms, CSD could begin in the primary visual cortex, in the primary somatosensory cortex or simultaneously in both, and propagate to the posterior parietal cortex, the temporal lobe and Broca's area. We believe that clinical descriptions of aura could play an important role in further investigations of the pathophysiology of migraine.

Correlations between brain cortical thickness and cutaneous pain thresholds are atypical in adults with migraine

BACKGROUND/OBJECTIVE

Migraineurs have atypical pain processing, increased expectations for pain, and hypervigilance for pain. Recent studies identified correlations between brain structure and pain sensation in healthy adults. The objective of this study was to compare cortical thickness-to-pain threshold correlations in migraineurs to healthy controls. We hypothesized that migraineurs would have aberrant relationships between the anatomical neurocorrelates of pain processing and pain thresholds.

METHODS

Pain thresholds to cutaneously applied heat were determined for 31 adult migraineurs and 32 healthy controls. Cortical thickness was determined from magnetic resonance imaging T1-weighted sequences. Regional cortical thickness-to-pain threshold correlations were determined for migraineurs and controls separately using a general linear model whole brain vertex-wise analysis. A pain threshold-by-group interaction analysis was then conducted to estimate regions where migraineurs show alterations in the pain threshold-to-cortical thickness correlations relative to healthy controls.

RESULTS

Controls had negative correlations (p<0.01 uncorrected) between pain thresholds and cortical thickness in left posterior cingulate/precuneus, right superior temporal, right inferior parietal, and left inferior temporal regions, and a negative correlation (p<0.01 Monte Carlo corrected) with a left superior temporal/inferior parietal region. Migraineurs had positive correlations (p<0.01 uncorrected) between pain thresholds and cortical thickness in left superior temporal/inferior parietal, right precuneus, right superior temporal/inferior parietal, and left inferior parietal regions. Cortical thickness-to-pain threshold correlations differed between migraine and control groups (p<0.01 uncorrected) for right superior temporal/inferior parietal, right precentral, left posterior cingulate/precuneus, and right inferior parietal regions and (p<0.01 Monte Carlo corrected) for a left superior temporal/inferior parietal region.

CONCLUSIONS

Unlike healthy control subjects who have a significant negative correlation between cortical thickness in a superior temporal/inferior parietal region with pain thresholds, migraineurs have a non-significant positive correlation between cortical thickness in a superior temporal/inferior parietal region with pain thresholds. Since this region participates in orienting and attention to painful stimuli, absence of the normal correlation might represent a migraineurs inability to inhibit pain sensation via shifting attention away from the painful stimulus.

Structural gray matter abnormalities in migraine relate to headache lateralization, but not aura

Background

The hallmark of migraine aura (MA) is transient cortical dysfunction but it is not known if MA is associated with structural cortical or subcortical changes. To determine the relation between MA and structural gray matter abnormalities, we studied a unique sample of 20 patients with frequent side-locked MA, i.e. visual aura consistently occurring in the same hemifield.

Methods

We applied a highly sensitive within-patient design to assess anatomical differences with both voxel-based morphometry and surface-based morphometry on a whole-hemisphere level and for specific anatomical regions of interest. Within-subject comparisons were made with regard to aura symptoms ( N = 20 vs 20) and with regard to headache ( N = 13 vs 13).

Results

We found no differences in gray matter structure with regard to aura symptoms in MA patients. Comparing the typical migraine headache side of the patients to the contralateral side revealed a difference in cortical thickness in the inferior frontal gyrus (mean difference 0.12 mm, p = 0.036).

Conclusion

MA per se is associated with abnormal function but not with lateralized abnormalities of gray matter structure. Alteration of the inferior frontal cortex suggests structural reorganization of pain inhibitory circuits in response to the repeated intense nociceptive input due to the headache attacks.

Atypical age-related cortical thinning in episodic migraine

Background

Prior studies demonstrate reduced cortical thickness and volume in migraineurs. However, the effect of age on cortical thickness has not been assessed in migraineurs. In this study we investigated whether the process of aging on cortical thickness affects migraineurs differently compared to age-matched healthy controls, i.e. whether aging exacerbates cortical thinning in migraineurs.

Methods

Cortical thickness was estimated using a general linear model vertex-by-vertex approach for 32 healthy controls (mean age = 35.3 years; SD = 11.6) and 27 episodic migraine patients (mean age = 33.6 years; SD = 12.3). Results were modeled using a main effect analysis to estimate the effect of age on cortical thickness for each group separately, and an age-by-group analysis to estimate differences in age-related cortical thinning between migraine patients and normal controls.

Results

Although migraineurs and normal controls both have expected age-related thinning in many regions along the cortical mantle, migraineurs have age-related thinning of regions that do not thin in healthy controls, including: bilateral postcentral, right fusiform, and right temporal pole areas. Cortical thinning of these regions is more prominent with advancing age.

Conclusion

Results suggest that migraine is associated with atypical cortical aging, suggesting that the migraine disease process interacts with aging to affect cortical integrity.

Thickening of the somatosensory cortex in migraine without aura

OBJECTIVE

We aimed to explore cortical thickness abnormalities in a homogeneous group of patients with migraine without aura and to delineate possible relationships between cortical thickness changes and clinical variables.

METHODS

Fifty-six female migraine patients without aura and T2-visible white matter hyperintensities and 34 female controls were scanned on a 3T magnetic resonance imager. Cortical thickness was estimated and compared between patients and controls using a whole-brain vertex-by-vertex analysis. Correlation analysis was conducted between cortical thickness of significant clusters and clinical variables.

RESULTS

Compared to controls, migraine patients had cortical thickening in left rostral middle frontal gyrus and bilateral post-central gyri. Region-of-interest analysis revealed cortical thickening of bilateral post-central gyri in migraine patients relative to controls. The average thickness of bilateral post-central gyri positively correlated with disease duration as well as estimated lifetime headache frequency.

CONCLUSIONS

We have provided evidence for interictal cortical abnormalities of thickened prefrontal cortex and somatosensory cortex in female migraine patients without aura. Our findings of greater thickening of the somatosensory cortex in relation to increasing disease duration and increasing headache frequency suggest that repeated migraine attacks over time may lead to structural changes of the somatosensory cortex through increased noxious afferent input within the trigemino-thalamo-cortical pathway in migraine.

Brain functional connectivity and morphology changes in medication-overuse headache: Clue for dependence-related processes?

BACKGROUND

Several imaging studies have identified localized anatomical and functional brain changes in medication-overuse headache (MOH).

OBJECTIVE

The objective of this article is to evaluate whole-brain functional connectivity at rest together with voxel-based morphometry in MOH patients, in comparison with episodic migraine (EM) patients and healthy controls (HCs).

METHODS

Anatomical MRI and resting-state functional MRI scans were obtained in MOH patients (n = 17 and 9, respectively), EM patients (n = 18 and 15, respectively) and HCs (n = 17 and 17). SPM8 was used to analyze voxel-based morphometry and seed (left precuneus) to voxel connectivity data in the whole brain.

RESULTS

Functional connectivity at rest was altered in MOH patients. Connectivity was decreased between precuneus and regions of the default-mode network (frontal and parietal cortices), but increased between precuneus and hippocampal/temporal areas. These functional modifications were not accompanied by significant gross morphological changes. Furthermore, connectivity between precuneus and frontal areas in MOH was negatively correlated with migraine duration and positively correlated with self-evaluation of medication dependence. Gray matter volumes of frontal regions, precuneus and hippocampus were also negatively related to migraine duration. Functional connectivity within the default-mode network appeared to predict anxiety scores of MOH patients while gray matter volumes in this network predicted their depression scores.

CONCLUSIONS

Our data suggest that MOH is associated with functional alterations within intrinsic brain networks rather than with macrostructural changes. They also support the view that dependence-related processes might play a prominent role in its development and maintenance.

Cortical spreading depression and central pain networks in trigeminal nuclei modulation: time for an integrated migraine pathogenesis perspective

The role of the cortical spreading depression (CSD)-dependent trigeminovascular activation in migraine etiopathogenesis, long considered paradigmatic, has remained substantially unproven in humans. The parallel advancement of functional neuroimaging techniques promoted the extensive exploration of the brain networks involved in pain processing in search of a possible central migraine generator. However, despite initial enthusiasms, it has not been possible to clarify whether the functional central "markers" of pain observed in primary headaches could be considered as causative or just the neural correlates of the ongoing pain. Nonetheless, our knowledge on the complex interactions between CSD, neurogenic inflammation, peripheral trigeminovascular input, central cortico-trigeminal nuclei direct modulation and pain processing and limbic system networks has enormously grown, allowing the reconceptualisation of migraine from a neurovascular to a pure neurolimbic pain disorder, therefore relocating it in the much broader frame of the brain and whole organism homeostatic control. In this work, the available evidences currently supporting the relevance of CSD, of peripheral trigeminovascular input and of direct cortico-trigeminal nuclei modulation in migraine pathogenesis are reviewed in the light of a possible integrated migraine etiopathogenetic perspective.

Regional neuroplastic brain changes in patients with chronic inflammatory and non-inflammatory visceral pain

Regional cortical thickness alterations have been reported in many chronic inflammatory and painful conditions, including inflammatory bowel diseases (IBD) and irritable bowel syndrome (IBS), even though the mechanisms underlying such neuroplastic changes remain poorly understood. In order to better understand the mechanisms contributing to grey matter changes, the current study sought to identify the differences in regional alterations in cortical thickness between healthy controls and two chronic visceral pain syndromes, with and without chronic gut inflammation. 41 healthy controls, 11 IBS subjects with diarrhea, and 16 subjects with ulcerative colitis (UC) underwent high-resolution T1-weighted magnetization-prepared rapid acquisition gradient echo scans. Structural image preprocessing and cortical thickness analysis within the region of interests were performed by using the Laboratory of Neuroimaging Pipeline. Group differences were determined using the general linear model and linear contrast analysis. The two disease groups differed significantly in several cortical regions. UC subjects showed greater cortical thickness in anterior cingulate cortical subregions, and in primary somatosensory cortex compared with both IBS and healthy subjects. Compared with healthy subjects, UC subjects showed lower cortical thickness in orbitofrontal cortex and in mid and posterior insula, while IBS subjects showed lower cortical thickness in the anterior insula. Large effects of correlations between symptom duration and thickness in the orbitofrontal cortex and postcentral gyrus were only observed in UC subjects. The findings suggest that the mechanisms underlying the observed gray matter changes in UC subjects represent a consequence of peripheral inflammation, while in IBS subjects central mechanisms may play a primary role.

Stimulation of dural vessels excites the SI somatosensory cortex of the cat via a relay in the thalamus

Aim

We carried out experiments in cats to determine the thalamo-cortical projection sites of trigeminovascular sensory neurons.

Methods

1) We stimulated the middle meningeal artery (MMA) with C-fibre intensity electrical shocks and made field potential recordings over the somatosensory cortical surface. 2) We then recorded neurons in the ventroposteromedial (VPM) nucleus of the thalamus in search of neurons which could be activated from the skin, MMA and superior sagittal sinus. 3) Finally, we attempted to antidromically activate the neurons found in stage 2 by stimulating the responsive cortical areas revealed in stage 1.

Results

VPM neurons received trigeminovascular input, input from the V1 facial skin and could also be activated by electrical stimulation of the somatosensory cortex. VPM neurons activated from the cortex responded with short and invariant latencies (6.7 ± 7.7 msec mean and SD). They could follow high rates of stimulation and sometimes showed collision with orthodromic action potentials.

Conclusions

We conclude that somatosensory (SI) cortical stimulation excites trigeminovascular VPM neurons antidromically. In consequence, these VPM neurons project to the somatosensory cortex. These findings may help to explain the ability of migraineurs with headache in the trigeminal distribution to localise their pain to a particular region in this distribution.

Recent progress in migraine pathophysiology: role of cortical spreading depression and magnetic resonance imaging

Migraine is characterised by debilitating pain, which affects the quality of life in affected patients in both the western and the eastern worlds. The purpose of this article is to give a detailed outline of the pathophysiology of migraine pain, which is one of the most confounding pathologies among pain disorders in clinical conditions. We critically evaluate the scientific basis of various theories concerning migraine pathophysiology, and draw insights from brain imaging approaches that have unraveled the prevalence of cortical spreading depression (CSD) in migraine. The findings supporting the role of CSD as a physiological substrate in clinical pain are discussed. We also give an exhaustive overview of brain imaging approaches that have been employed to solve the genesis of migraine pain, and its possible links to the brainstem, the neocortex, genetic endophenotypes, and pathogenetic factors (such as dopaminergic hypersensitivity). Furthermore, a roadmap is proposed to provide a better understanding of pain pathophysiology in migraine, to enable the development of strategies using leads from brain imaging studies for the identification of early biomarkers, efficient prognosis, and treatment planning, which eventually may help in alleviating some of the devastating impact of pain morbidity in patients afflicted with migraine.

Putative physiological mechanisms underlying tDCS analgesic effects

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that induces changes in excitability, and activation of brain neurons and neuronal circuits. It has been observed that beyond regional effects under the electrodes, tDCS also alters activity of remote interconnected cortical and subcortical areas. This makes the tDCS stimulation technique potentially promising for modulation of pain syndromes. Indeed, utilizing specific montages, tDCS resulted in analgesic effects in experimental settings, as well as in post-operative acute pain and chronic pain syndromes. The promising evidence of tDCS-induced analgesic effects raises the challenging and complex question of potential physiologic mechanisms that underlie/mediate the accomplished pain relief. Here we present hypotheses on how the specific montages and targets for stimulation may affect the pain processing network.

Irritable bowel syndrome in female patients is associated with alterations in structural brain networks

Alterations in gray matter (GM) density/volume and cortical thickness (CT) have been demonstrated in small and heterogeneous samples of subjects with differing chronic pain syndromes, including irritable bowel syndrome (IBS). Aggregating across 7 structural neuroimaging studies conducted at University of California, Los Angeles, Los Angeles, CA, USA, between August 2006 and April 2011, we examined group differences in regional GM volume in 201 predominantly premenopausal female subjects (82 IBS, mean age: 32±10 SD, 119 healthy controls [HCs], 30±10 SD). Applying graph theoretical methods and controlling for total brain volume, global and regional properties of large-scale structural brain networks were compared between the group with IBS and the HC group. Relative to HCs, the IBS group had lower volumes in the bilateral superior frontal gyrus, bilateral insula, bilateral amygdala, bilateral hippocampus, bilateral middle orbital frontal gyrus, left cingulate, left gyrus rectus, brainstem, and left putamen. Higher volume was found in the left postcentral gyrus. Group differences were no longer significant for most regions when controlling for the Early Trauma Inventory global score, with the exception of the right amygdala and the left postcentral gyrus. No group differences were found for measures of global and local network organization. Compared to HCs, in patients with IBS, the right cingulate gyrus and right thalamus were identified as being significantly more critical for information flow. Regions involved in endogenous pain modulation and central sensory amplification were identified as network hubs in IBS. Overall, evidence for central alterations in patients with IBS was found in the form of regional GM volume differences and altered global and regional properties of brain volumetric networks.

S1 is associated with chronic low back pain: a functional and structural MRI study

A fundamental characteristic of neural circuits is the capacity for plasticity in response to experience. Neural plasticity is associated with the development of chronic pain disorders. In this study, we investigated 1) brain resting state functional connectivity (FC) differences between patients with chronic low back pain (cLBP) and matched healthy controls (HC); 2) FC differences within the cLBP patients as they experienced different levels of endogenous low back pain evoked by exercise maneuvers, and 3) morphometric differences between cLBP patients and matched HC. We found the dynamic character of FC in the primary somatosensory cortex (S1) in cLBP patients, i.e., S1 FC decreased when the patients experienced low intensity LBP as compared with matched healthy controls, and FC at S1 increased when cLBP patients experienced high intensity LBP as compared with the low intensity condition. In addition, we also found increased cortical thickness in the bilateral S1 somatotopically associated with the lower back in cLBP patients as compared to healthy controls. Our results provide evidence of structural plasticity co-localized with areas exhibiting FC changes in S1 in cLBP patients.

Sensorimotor and Pain Modulation Brain Abnormalities in Trigeminal Neuralgia: A Paroxysmal, Sensory-Triggered Neuropathic Pain

OBJECTIVE

Idiopathic trigeminal neuralgia (TN) is characterized by paroxysms of severe facial pain but without the major sensory loss that commonly accompanies neuropathic pain. Since neurovascular compression of the trigeminal nerve root entry zone does not fully explain the pathogenesis of TN, we determined whether there were brain gray matter abnormalities in a cohort of idiopathic TN patients. We used structural MRI to test the hypothesis that TN is associated with altered gray matter (GM) in brain areas involved in the sensory and affective aspects of pain, pain modulation, and motor function. We further determined the contribution of long-term TN on GM plasticity.

METHODS

Cortical thickness and subcortical GM volume were measured from high-resolution 3T T1-weighted MRI scans in 24 patients with right-sided TN and 24 healthy control participants.

RESULTS

TN patients had increased GM volume in the sensory thalamus, amygdala, periaqueductal gray, and basal ganglia (putamen, caudate, nucleus accumbens) compared to healthy controls. The patients also had greater cortical thickness in the contralateral primary somatosensory cortex and frontal pole compared to controls. In contrast, patients had thinner cortex in the pregenual anterior cingulate cortex, the insula and the orbitofrontal cortex. No relationship was observed between GM abnormalities and TN pain duration.

CONCLUSIONS

TN is associated with GM abnormalities in areas involved in pain perception, pain modulation and motor function. These findings may reflect increased nociceptive input to the brain, an impaired descending modulation system that does not adequately inhibit pain, and increased motor output to control facial movements to limit pain attacks.

Clinical use of brain volumetry

Magnetic resonance imaging (MRI)-based brain volumetry is increasingly being used in the clinical setting to assess brain volume changes from structural MR images in a range of neurologic conditions. Measures of brain volumes have been shown to be valid biomarkers of the clinical state and progression by offering high reliability and robust inferences on the underlying disease-related mechanisms. This review critically examines the different scenarios of the application of MRI-based brain volumetry in neurology: 1) supporting disease diagnosis, 2) understanding mechanisms and tracking clinical progression of disease, and 3) monitoring treatment effect. These aspects will be discussed in a wide range of neurologic conditions, with particular emphasis on Alzheimer's disease and multiple sclerosis.

Brain imaging in migraine research

Understanding the pathophysiology and pharmacology of migraine has been driven by astute clinical observations, elegant experimental medicine studies, and importantly by studying highly effective anti-migraine agents in the laboratory and the clinic. Significant progress has been made in the use of functional brain imaging to compliment observational studies of migraine phenotypes by highlighting pathways within the brain that may be involved in predisposition to migraine, modulating migraine pain or that could be sensitive to pharmacological or behavioral therapeutic intervention. In drug discovery, molecular imaging approaches compliment functional neuroimaging by visualizing migraine drug targets within the brain. Molecular imaging enables the selection and evaluation of drug candidates by confirming that they engage their targets sufficiently at well tolerated doses to test our therapeutic hypotheses. Migraine is a progressive disorder. Developing our knowledge of where drugs act in the brain and of how the brain is altered in both episodic migraine (interictal state and ictal state) and chronic migraine are important steps to understanding why there is such differential responsiveness to therapeutics among migraine patients and to improving how they are evaluated and treated.

Ventral posterolateral deep brain stimulation treatment for neuropathic pain shortens pain response after cold stimuli

Neuropathic pain is often severe. Deep brain stimulation (DBS) is a treatment method for neuropathic pain, but its mechanism of action remains unclear. Patients with neuropathic pain are affected by various stimulations, such as mechanical and cold stimuli, but studies of cold allodynia showed the associated pain to be less than that caused by mechanical stimuli. This study focused on the effects of DBS on cold allodynia in rats. To observe the effects of DBS, we established three groups: a normal group (normal), a neuropathic pain group (pain), and a DBS with neuropathic pain group (DBS). The stimulation target was the ventral posterolateral nucleus (VPL). We observed differences in the degree of cold allodynia elicited between a conventional method that measured the number of pain responses and our altered novel method that measured the duration of pain responses. Cold allodynia after DBS did not differ when conventional analysis was applied, but the pain response duration was decreased. We suggest that VPL DBS was partially effective in cold allodynia, implicating complex pathways of pain signaling.

Cortical abnormalities in patients with migraine: a surface-based analysis

PURPOSE

To explore the patterns of cortical thickness and cortical surface area abnormalities in patients with migraine (with the expectation of seeing reduced cortical thickness and surface area in regions subserving nociception and increased cortical thickness and surface area in regions involved in migraine pathogenesis) and to assess their correlation with clinical and radiologic manifestations of the disease.

MATERIALS AND METHODS

Approval of the local ethical committee was obtained, as well as written informed consent from each participant. T2-weighted and three-dimensional T1-weighted magnetic resonance images of the brain were acquired in 63 migraineurs and 18 matched healthy control subjects. Cortical thickness and cortical surface area were estimated. By using a general linear model approach, a vertex-by-vertex statistical analysis (P < .01) was used to assess between-group comparisons (migraineurs vs control subjects, the aura effect, the effect of white matter hyperintensities [WMHs]) and the correlations between cortical thickness and surface area measurements and patients' clinical and radiologic characteristics.

RESULTS

Compared with control subjects, patients with migraine showed reduced cortical thickness and surface area in regions subserving pain processing (P < .01). These two metrics were increased in regions involved in executive functions and visual motion processing (P < .01). The anatomic overlap of cortical thickness and cortical surface area abnormalities was only minimal, with cortical surface area abnormalities being more pronounced and more widely distributed than cortical thickness abnormalities. Cortical thickness and surface area abnormalities were related to aura and WMHs (P < .01) but not to disease duration and attack frequency.

CONCLUSION

Cortical abnormalities occur in migraineurs and may represent the results of a balance between an intrinsic predisposition, as suggested by cortical surface area abnormalities, and disease-related processes, as indicated by cortical thickness abnormalities.

Hierarchical alteration of brain structural and functional networks in female migraine sufferers

BACKGROUND

Little is known about the changes of brain structural and functional connectivity networks underlying the pathophysiology in migraine. We aimed to investigate how the cortical network reorganization is altered by frequent cortical overstimulation associated with migraine.

METHODOLOGY/PRINCIPAL FINDINGS

Gray matter volumes and resting-state functional magnetic resonance imaging signal correlations were employed to construct structural and functional networks between brain regions in 43 female patients with migraine (PM) and 43 gender-matched healthy controls (HC) by using graph theory-based approaches. Compared with the HC group, the patients showed abnormal global topology in both structural and functional networks, characterized by higher mean clustering coefficients without significant change in the shortest absolute path length, which indicated that the PM lost optimal topological organization in their cortical networks. Brain hubs related to pain-processing revealed abnormal nodal centrality in both structural and functional networks, including the precentral gyrus, orbital part of the inferior frontal gyrus, parahippocampal gyrus, anterior cingulate gyrus, thalamus, temporal pole of the middle temporal gyrus and the inferior parietal gyrus. Negative correlations were found between migraine duration and regions with abnormal centrality. Furthermore, the dysfunctional connections in patients' cortical networks formed into a connected component and three dysregulated modules were identified involving pain-related information processing and motion-processing visual networks.

CONCLUSIONS

Our results may reflect brain alteration dynamics resulting from migraine and suggest that long-term and high-frequency headache attacks may cause both structural and functional connectivity network reorganization. The disrupted information exchange between brain areas in migraine may be reshaped into a hierarchical modular structure progressively.

Structural and functional neuroimaging in migraine: insights from 3 decades of research

Modern imaging methods provide unprecedented insights into brain structure, perfusion, metabolism, and neurochemistry, both during and between migraine attacks. Neuroimaging investigations conducted in recent decades bring us closer to uncovering migraine as a multifaceted, primarily central nervous system disorder. Three main categories of structural and functional brain changes are described in this review, corresponding to the migrainous aura, ictal headache, and interictal states. These changes greatly advance our understanding of multiple pathophysiologic underpinnings of migraine, from central "migraine generating" loci, to cortical spreading depression, intimate mechanisms underlying activation of neuronal pain pathways in vulnerable patients, central sensitization, and chronification. Structural imaging begins to explain the complex connections between migraine and cerebral vascular events, white matter lesions, grey matter density alterations, iron deposition, and microstructural brain damage. Selected structural and functional alterations of brain structures, as identified with imaging methods, may represent the foundation of new diagnostic strategies and serve as markers of therapeutic efficacy.

Grey matter changes associated with medication-overuse headache: correlations with disease related disability and anxiety

OBJECTIVES

Medication-overuse headache (MOH) is associated with psychiatric comorbidities. Neurobiological similarities to substance dependence have been suggested. This study investigated grey matter changes, focussing on pain and reward systems.

METHODS

Using voxel-based morphometry, structural MRIs were compared between 29 patients with both, MOH and migraine, according to International Headache Society criteria, and healthy controls. The Migraine Disability Assessment (MIDAS) score was used. Anxiety and depression were screened for with the Hospital Anxiety and Depression Scale (HADS) and confirmed by a psychiatrist, using the Mini International Neuropsychiatric Interview.

RESULTS

Nineteen patients (66%) had a present or past psychiatric disorder, mainly affective (N = 11) and anxiety disorders (N = 8). In all patients a significant increase of grey matter volume (GMV) was found in the periaqueductal grey matter of the midbrain, which correlated positively with the MIDAS and the HADS-anxiety subscale. A GMV increase was found bilaterally in the thalamus, and the ventral striatum. A significant GMV decrease was detected in frontal regions including orbitofrontal cortex, anterior cingulate cortex, the left and right insula, and the precuneus.

CONCLUSION

These findings are consistent with dysfunction of antinociceptive systems in MOH, which is influenced by anxiety. Dysfunction of the reward system may be a neurobiological basis for dependence in a subgroup of MOH patients.

Migraine changes the brain: neuroimaging makes its mark

PURPOSE OF REVIEW

This review summarizes key findings of the current literature on functional neuroimaging in migraine and describes how these studies have changed our view of the disorder.

RECENT FINDINGS

Recent studies have started not only to investigate the global cerebral activation pattern during migraine attacks, but to address specific aspects of migraine attacks such as photophobia, osmophobia as well as pain perception with the aim of disentangling the underlying mechanisms. There is also more and more evidence that the migraine brain is abnormal even outside of attacks and that repeated attacks are leading to functional and structural alterations in the brain, which may in turn drive the transformation of migraine to its chronic form. Some new results are pinpointing toward a potential role of interesting new brain areas in migraine pathophysiology such as the temporal cortex or the basal ganglia.

SUMMARY

Neuroimaging studies are beginning to shed light on the mechanisms underlying the development and evolution of migraine and its specific symptoms. Future studies have the potential to also improve our understanding of established and upcoming treatment approaches and to monitor treatment effects in an objective and noninvasive way.