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1.  Anatomical Alterations of the Visual Motion Processing Network in Migraine with and without Aura 
PLoS Medicine  2006;3(10):e402.
Background
Patients suffering from migraine with aura (MWA) and migraine without aura (MWoA) show abnormalities in visual motion perception during and between attacks. Whether this represents the consequences of structural changes in motion-processing networks in migraineurs is unknown. Moreover, the diagnosis of migraine relies on patient's history, and finding differences in the brain of migraineurs might help to contribute to basic research aimed at better understanding the pathophysiology of migraine.
Methods and Findings
To investigate a common potential anatomical basis for these disturbances, we used high-resolution cortical thickness measurement and diffusion tensor imaging (DTI) to examine the motion-processing network in 24 migraine patients (12 with MWA and 12 MWoA) and 15 age-matched healthy controls (HCs). We found increased cortical thickness of motion-processing visual areas MT+ and V3A in migraineurs compared to HCs. Cortical thickness increases were accompanied by abnormalities of the subjacent white matter. In addition, DTI revealed that migraineurs have alterations in superior colliculus and the lateral geniculate nucleus, which are also involved in visual processing.
Conclusions
A structural abnormality in the network of motion-processing areas could account for, or be the result of, the cortical hyperexcitability observed in migraineurs. The finding in patients with both MWA and MWoA of thickness abnormalities in area V3A, previously described as a source in spreading changes involved in visual aura, raises the question as to whether a “silent” cortical spreading depression develops as well in MWoA. In addition, these experimental data may provide clinicians and researchers with a noninvasively acquirable migraine biomarker.
A structural abnormality in the network of motion-processing areas could account for, or be the result of, the cortical hyperexcitability seen in people who have migraine.
Editors' Summary
Background.
Migraine is a disabling brain disorder that affects more than one in ten people during their lifetimes. It is characterized by severe, recurrent headaches, often accompanied by nausea, vomiting, and light sensitivity. In some migraineurs (people who have migraines), the headaches are preceded by neurological disturbances known as “aura.” These usually affect vision, causing illusions of flashing lights, zig-zag lines, or blind spots. There are many triggers for migraine attacks—including some foods, stress, and bright lights—and every migraineur has to learn what triggers his or her attacks. There is no cure for migraine, although over-the-counter painkillers can ease the symptoms and doctors can prescribe stronger remedies or drugs to reduce the frequency of attacks. Exactly what causes migraine is unclear but scientists think that, for some reason, the brains of migraineurs are hyperexcitable. That is, some nerve cells in their brains overreact when they receive electrical messages from the body. This triggers a local disturbance of brain function called “cortical spreading depression,” which, in turn, causes aura, headache, and the other symptoms of migraine.
Why Was This Study Done?
Researchers need to know more about what causes migraine to find better treatments. One clue comes from the observation that motion perception is abnormal in migraineurs, even between attacks—they can be very sensitive to visually induced motion sickness, for example. Another clue is that aura are usually visual. So could brain regions that process visual information be abnormal in people who have migraines? In this study, the researchers investigated the structure of the motion processing parts of the brain in people who have migraine with aura, in people who have migraine without aura, and in unaffected individuals to see whether there were any differences that might help them understand migraine.
What Did the Researchers Do and Find?
The researchers used two forms of magnetic resonance imaging—a noninvasive way to produce pictures of internal organs—to examine the brains of migraineurs (when they weren't having a migraine) and healthy controls. They concentrated on two brain regions involved in motion processing known as the MT+ and V3A areas and first measured the cortical thickness of these areas—the cortex is the wrinkled layer of gray matter on the outside of the brain that processes information sent from the body. They found that the cortical thickness was increased in both of these areas in migraineurs when compared to healthy controls. There was no difference in cortical thickness between migraineurs who had aura and those who did not, but the area of cortical thickening in V3A corresponded to the source of cortical spreading depression previously identified in a person who had migraine with aura. The researchers also found differences between the white matter (the part of the brain that transfers information between different regions of the gray matter) immediately below the V3A and MT+ areas in the migraineurs and the controls but again not between the two groups of migraineurs.
What Do These Findings Mean?
This study provides new information about migraine. First, it identifies structural changes in the brains of people who have migraines. Until now, it has been thought that abnormal brain function causes migraine but that migraineurs have a normal brain structure. The observed structural differences might either account for or be caused by the hyperexcitability that triggers migraines. Because migraine runs in families, examining the brains of children of migraineurs as they grow up might indicate which of these options is correct, although it is possible that abnormalities in brain areas not examined here actually trigger migraines. Second, the study addresses a controversial question about migraine: Is migraine with aura the same as migraine without aura? The similar brain changes in both types of migraine suggest that they are one disorder. Third, the abnormalities in areas MT+ and V3A could help to explain why migraineurs have problems with visual processing even in between attacks. Finally, this study suggests that it might be possible to develop a noninvasive test to help doctors diagnose migraine.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0030402.
The MedlinePlus encyclopedia has several pages on migraine
The US National Institute of Neurological Disorders and Stroke offers patient information on migraine and other headaches
The NHS Direct Online contains patient information on migraine from the UK National Health Service
MAGNUM provides information from The US National Migraine Association
The Migraine Trust is a UK charity that supports research and provides support for patients
The Migraine Aura Foundation is a site about aura that includes a section on art and aura
doi:10.1371/journal.pmed.0030402
PMCID: PMC1609120  PMID: 17048979
2.  Studies on the Pathophysiology and Genetic Basis of Migraine 
Current Genomics  2013;14(5):300-315.
Migraine is a neurological disorder that affects the central nervous system causing painful attacks of headache. A genetic vulnerability and exposure to environmental triggers can influence the migraine phenotype. Migraine interferes in many facets of people’s daily life including employment commitments and their ability to look after their families resulting in a reduced quality of life. Identification of the biological processes that underlie this relatively common affliction has been difficult because migraine does not have any clearly identifiable pathology or structural lesion detectable by current medical technology. Theories to explain the symptoms of migraine have focused on the physiological mechanisms involved in the various phases of headache and include the vascular and neurogenic theories. In relation to migraine pathophysiology the trigeminovascular system and cortical spreading depression have also been implicated with supporting evidence from imaging studies and animal models. The objective of current research is to better understand the pathways and mechanisms involved in causing pain and headache to be able to target interventions. The genetic component of migraine has been teased apart using linkage studies and both candidate gene and genome-wide association studies, in family and case-control cohorts. Genomic regions that increase individual risk to migraine have been identified in neurological, vascular and hormonal pathways. This review discusses knowledge of the pathophysiology and genetic basis of migraine with the latest scientific evidence from genetic studies.
doi:10.2174/13892029113149990007
PMCID: PMC3763681  PMID: 24403849
Migraine; Migraine with aura; Migraine without aura; Familial hemiplegic migraine; Molecular genetics; Genes
3.  Pediatric migraine and episodic syndromes that may be associated with migraine 
Importance
Migraine is a common disorder and a frequent cause of medical consultation in children. Many childhood episodic syndromes have been described as common precursors of migraine.
Objective
To review current knowledge on migraine and childhood episodic syndromes, and to discuss future directions for research and clinical practice.
Findings
For most children it is difficult to describe a headache and fully verbalize symptoms such as photophobia and phonophobia that must be inferred from behaviour. Classical migraine features are rare before the age of 6 years, but some migraine-related syndromes have been described. Benign paroxysmal torticollis of infancy, benign paroxysmal vertigo of childhood, cyclic vomiting syndrome and abdominal migraine are currently classified as childhood episodic syndromes, and therefore common precursors of migraine. A strong association between infantile colic and migraine has recently been reported. There are similarities between children with episodic syndromes and children with migraine, regarding social and demographic factors, precipitating and relieving factors, and accompanying gastrointestinal, neurologic, and vasomotor features. The real pathophysiological mechanisms of migraine are not fully understood. Current data obtained through molecular and functional studies provide a complex model in which vascular and neurologic events cooperate in the pathogenesis of migraine attacks. Genetic factors causing disturbances in neuronal ion channels, make a migraineur more sensitive to multiple trigger factors that activate the nociception cascade. The expanding knowledge on migraine genetics and pathophysiology may be applicable to childhood episodic syndromes. Migraine preventive strategies are particularly important in children, and could be beneficial in childhood episodic syndromes. Nonspecific analgesics like ibuprofen and acetaminophen are widely used in pediatrics to control pain and have been found to be effective also in the treatment of acute migraine attacks. Triptans are the specific fist-line drugs for acute migraine treatment.
Conclusions and relevance
Migraine phenotype differs somewhat in the developing brain, and childhood episodic syndromes may arise before typical migraine headache. Diagnosing pediatric migraine may be difficult because of children’s language and cognitive abilities. The risk of underestimating migraine in pediatric age is high. An adequate diagnosis is important to maintain a good quality of life and to avoid inappropriate therapy.
doi:10.1186/s13052-014-0092-4
PMCID: PMC4239406  PMID: 25407042
Infantile colic; Migraine; Cyclic vomiting; Recurrent abdominal pain; Functional abdominal pain; Torticollis
4.  Selectivity in Genetic Association with Sub-classified Migraine in Women 
PLoS Genetics  2014;10(5):e1004366.
Migraine can be sub-classified not only according to presence of migraine aura (MA) or absence of migraine aura (MO), but also by additional features accompanying migraine attacks, e.g. photophobia, phonophobia, nausea, etc. all of which are formally recognized by the International Classification of Headache Disorders. It remains unclear how aura status and the other migraine features may be related to underlying migraine pathophysiology. Recent genome-wide association studies (GWAS) have identified 12 independent loci at which single nucleotide polymorphisms (SNPs) are associated with migraine. Using a likelihood framework, we explored the selective association of these SNPs with migraine, sub-classified according to aura status and the other features in a large population-based cohort of women including 3,003 active migraineurs and 18,108 free of migraine. Five loci met stringent significance for association with migraine, among which four were selective for sub-classified migraine, including rs11172113 (LRP1) for MO. The number of loci associated with migraine increased to 11 at suggestive significance thresholds, including five additional selective associations for MO but none for MA. No two SNPs showed similar patterns of selective association with migraine characteristics. At one extreme, SNPs rs6790925 (near TGFBR2) and rs2274316 (MEF2D) were not associated with migraine overall, MA, or MO but were selective for migraine sub-classified by the presence of one or more of the additional migraine features. In contrast, SNP rs7577262 (TRPM8) was associated with migraine overall and showed little or no selectivity for any of the migraine characteristics. The results emphasize the multivalent nature of migraine pathophysiology and suggest that a complete understanding of the genetic influence on migraine may benefit from analyses that stratify migraine according to both aura status and the additional diagnostic features used for clinical characterization of migraine.
Author Summary
Migraine is among the most common and debilitating neurological disorders. Diagnostic criteria for migraine recognize a variety of symptoms including a primary dichotomous classification for the presence or absence of aura, typically a visual disturbance phenomenon, as well as others such as sensitivity to light or sound, and nausea, etc. We explored whether any of 12 recently discovered genetic variants associated with common migraine might have selective association for migraine sub-classified by aura status or nine additional migraine features in a population of middle-aged women including 3,003 migraineurs and 18,180 non-migraineurs. Five of the 12 genetic variants met the most stringent significance criterion for association with migraine, among which four had selective association with sub-classified migraine, including one that was selective for migraine without aura. At suggestive significance, all of the remaining genetic variants were selective for sub-classifications of migraine although no two variants showed the same pattern of selectivity. The selectivity patterns suggest very different contributions to migraine pathophysiology among the 12 loci and their implicated genes. Further, the results suggest that future discovery efforts for new migraine susceptibility loci would benefit by considering associations with sub-classified migraine toward the ultimate goals of more specific diagnosis and personalized treatment.
doi:10.1371/journal.pgen.1004366
PMCID: PMC4031047  PMID: 24852292
5.  Migraine Features, Associated Symptoms, and Triggers: A Principal Component Analysis in the Women's Health Study 
Aims
Migraine has a wide clinical spectrum. Our aim was to group information on migraine characteristics into meaningful components and to identify key components of the migraine phenotype.
Methods
We performed two principal component analyses, one among participants in the Women's Health Study enrolment cohort and one in a sub-cohort with additional migraine-specific information.
Results
Among the 9,427 women with migraine attack-related information at enrolment, the three most important components pertained to central nervous system (CNS) sensitization, attack frequency/pain location, and aura/visual phenomena. In the sub-group of 1,675 women with more detailed information, food triggers and unspecific symptoms constituted two principal components that explain more of the variance of the migraine phenotype than the three attack-related components.
Conclusions
Our results indicate that information on migraine-associated features, symptoms, and triggers is highly correlated allowing the extraction of principal components. Migraine attack-related symptoms are best summarized by symptoms related to CNS sensitization, attack frequency/pain location, and aura/visual phenomena. Taking a more general view, unspecific symptoms and food triggers appear to carry stronger importance in characterizing the migraine phenotype. These components are useful for future research on the pathophysiology and genetics of migraine and may have implications for diagnosing and treating patients.
doi:10.1177/0333102411401635
PMCID: PMC3100409  PMID: 21398421
migraine; features; triggers; sensitization; principal component analysis
6.  The pathophysiology of migraine: year 2005 
The Journal of Headache and Pain  2005;6(3):105-111.
Migraine is a complex patholophysiology in which both central and peripheral components of the trigeminal pain pathway probably play a significant role, both in the symptoms and signs of the attack and in the mechanisms of action of antimigraine compounds, such as triptans, which constitute the most important therapy for aborting migraine pain and posses several mechanisms on 5–HT receptor–mediated actions. The experimental neurogenic inflammation model represents a simple procedure to obtain preliminary information on well characterized receptortargeted drugs. The apparent paradox observed with certain drugs that are shown to be effective in this model but not in clinical trials offers the opportunity to better manipulate structure–activity to obtain the best pharmacological profile using an array of experimental models. The observation that nitric oxide donors induce migraine–like pain in migraineours and that nitric oxide plays a pivotal role in the control of several functions in the central nervous system, has prompted the use of such molecules for better understanding the pathophysiology of migraine attacks. A link between central and peripheral components of the trigeminal pain pathway is provided by the observation that cortical spreading depression in the rat activates trigeminovascular afferents and induces a series of cortical meningeal and brainstem events consistent with the development of headache. Studies in humans support the hypothesis that cortical spreading depression underlies migraine.aura. Therefore, tt is possible that visual, motor or sensory aura might be responsible for the generation of the pain through the above mechanisms
doi:10.1007/s10194-005-0165-2
PMCID: PMC3451639  PMID: 16355290
Trigeminovascular system; Neurogenic inflammation; Nitric oxide; Cortical Spreading depression; Migraine aura
7.  Variants in the human potassium channel gene (KCNN3) are associated with migraine in a high risk genetic isolate 
The Journal of Headache and Pain  2011;12(6):603-608.
The calcium-activated potassium ion channel gene (KCNN3) is located in the vicinity of the familial hemiplegic migraine type 2 locus on chromosome 1q21.3. This gene is expressed in the central nervous system and plays a role in neural excitability. Previous association studies have provided some, although not conclusive, evidence for involvement of this gene in migraine susceptibility. To elucidate KCNN3 involvement in migraine, we performed gene-wide SNP genotyping in a high-risk genetic isolate from Norfolk Island, a population descended from a small number of eighteenth century Isle of Man ‘Bounty Mutineer’ and Tahitian founders. Phenotype information was available for 377 individuals who are related through the single, well-defined Norfolk pedigree (96 were affected: 64 MA, 32 MO). A total of 85 SNPs spanning the KCNN3 gene were genotyped in a sub-sample of 285 related individuals (76 affected), all core members of the extensive Norfolk Island ‘Bounty Mutineer’ genealogy. All genotyping was performed using the Illumina BeadArray platform. The analysis was performed using the statistical program SOLAR v4.0.6 assuming an additive model of allelic effect adjusted for the effects of age and sex. Haplotype analysis was undertaken using the program HAPLOVIEW v4.0. A total of four intronic SNPs in the KCNN3 gene displayed significant association (P < 0.05) with migraine. Two SNPs, rs73532286 and rs6426929, separated by approximately 0.1 kb, displayed complete LD (r2 = 1.00, D′ = 1.00, D′ 95% CI = 0.96–1.00). In all cases, the minor allele led to a decrease in migraine risk (beta coefficient = 0.286–0.315), suggesting that common gene variants confer an increased risk of migraine in the Norfolk pedigree. This effect may be explained by founder effect in this genetic isolate. This study provides evidence for association of variants in the KCNN3 ion channel gene with migraine susceptibility in the Norfolk genetic isolate with the rarer allelic variants conferring a possible protective role. This the first comprehensive analysis of this potential candidate gene in migraine and also the first study that has utilised the unique Norfolk Island large pedigree isolate to implicate a specific migraine gene. Studies of additional variants in KCNN3 in the Norfolk pedigree are now required (e.g. polyglutamine variants) and further analyses in other population data sets are required to clarify the association of the KCNN3 gene and migraine risk in the general outbred population.
doi:10.1007/s10194-011-0392-7
PMCID: PMC3208049  PMID: 22030984
Migraine; Norfolk Island; Association; Population isolate; KCNN3
8.  Variants in the human potassium channel gene (KCNN3) are associated with migraine in a high risk genetic isolate 
The Journal of Headache and Pain  2011;12(6):603-608.
The calcium-activated potassium ion channel gene (KCNN3) is located in the vicinity of the familial hemiplegic migraine type 2 locus on chromosome 1q21.3. This gene is expressed in the central nervous system and plays a role in neural excitability. Previous association studies have provided some, although not conclusive, evidence for involvement of this gene in migraine susceptibility. To elucidate KCNN3 involvement in migraine, we performed gene-wide SNP genotyping in a high-risk genetic isolate from Norfolk Island, a population descended from a small number of eighteenth century Isle of Man ‘Bounty Mutineer’ and Tahitian founders. Phenotype information was available for 377 individuals who are related through the single, well-defined Norfolk pedigree (96 were affected: 64 MA, 32 MO). A total of 85 SNPs spanning the KCNN3 gene were genotyped in a sub-sample of 285 related individuals (76 affected), all core members of the extensive Norfolk Island ‘Bounty Mutineer’ genealogy. All genotyping was performed using the Illumina BeadArray platform. The analysis was performed using the statistical program SOLAR v4.0.6 assuming an additive model of allelic effect adjusted for the effects of age and sex. Haplotype analysis was undertaken using the program HAPLOVIEW v4.0. A total of four intronic SNPs in the KCNN3 gene displayed significant association (P < 0.05) with migraine. Two SNPs, rs73532286 and rs6426929, separated by approximately 0.1 kb, displayed complete LD (r2 = 1.00, D′ = 1.00, D′ 95% CI = 0.96–1.00). In all cases, the minor allele led to a decrease in migraine risk (beta coefficient = 0.286–0.315), suggesting that common gene variants confer an increased risk of migraine in the Norfolk pedigree. This effect may be explained by founder effect in this genetic isolate. This study provides evidence for association of variants in the KCNN3 ion channel gene with migraine susceptibility in the Norfolk genetic isolate with the rarer allelic variants conferring a possible protective role. This the first comprehensive analysis of this potential candidate gene in migraine and also the first study that has utilised the unique Norfolk Island large pedigree isolate to implicate a specific migraine gene. Studies of additional variants in KCNN3 in the Norfolk pedigree are now required (e.g. polyglutamine variants) and further analyses in other population data sets are required to clarify the association of the KCNN3 gene and migraine risk in the general outbred population.
doi:10.1007/s10194-011-0392-7
PMCID: PMC3208049  PMID: 22030984
Migraine; Norfolk Island; Association; Population isolate; KCNN3
9.  Neurological mechanisms of migraine: potential of the gap-junction modulator tonabersat in prevention of migraine 
Migraine is a neurovascular disorder characterized by recurrent episodic headaches, and is caused by abnormal processing of sensory information due to peripheral and/or central sensitization. The exact pathophysiological mechanism underlying migraine is not fully understood; however, cortical spreading depression (CSD) is thought to provide the basis for migraine aura and may serve as a trigger of migraine pain. CSD depends on neuronal–glial cell communication, which is mediated by intercellular transfer of messengers through connexin-containing gap junctions, as well as messengers released into the extracellular space by non-junctional connexin-containing hemichannels. These processes are believed to be important in peripheral sensitization within the trigeminal ganglion and to lead to central sensitization. The novel benzopyran compound tonabersat binds selectively to a unique site in the brain. In preclinical studies, tonabersat markedly reduced CSD and CSD-associated events and inhibited gap-junction communication between neurons and satellite glial cells in the trigeminal ganglion. Together, these findings suggest that tonabersat should have clinical application in preventing migraine attacks.
doi:10.1111/j.1468-2982.2009.01976.x
PMCID: PMC3142555  PMID: 19723120
Connexins; cortical spreading depression; gap junctions; tonabersat; trigeminovascular
10.  Molecular mechanisms of antimigraine drugs: past, present, and future 
The Journal of Headache and Pain  2004;5(Suppl 2):s99-s102.
Pharmacotherapeutic treatments for migraine have been documented for more than a century. Drugs that are effective in aborting an ongoing migraine attack exhibit a diversity of molecular mechanisms of action, but usually produce constriction of cranial arterial blood vessels, reversal of neurogenic inflammatory processes, and/or inhibition of sensory neuronal firing. This general understanding of drug action has led to the development of a unitary hypothesis for migraine pathophysiology, in which the onset of migraine is associated with activation of the trigemino-vascular system. Drugs which inhibit or reverse the activation of this system are effective acute treatments for migraine. Drugs useful in migraine prophylaxis have been discovered largely serendipitously, and display a fundamentally different pharmacology to the acutely effective agents. These drugs act at membrane receptors and ion channels, or by targeting intracellular biochemical pathways, and tend to reduce neuronal excitability in higher centers of the CNS. However, other than to suggest that this inhibits various migraine trigger events, it is not yet possible to delineate precisely how these drugs act to decrease the frequency and severity of migraine attacks. More recently, it has been observed that migraine is accompanied by sensory neuronal central sensitization that manifests as cutaneous allodynia in territory innervated by the trigeminal nerve. Although little is presently known about the ability of prophylactic drugs to modulate this process, it was recently shown that acute relief of migraine with triptan drugs is only reliably achieved when the drugs are given prior to the development of central sensitization. This important observation suggests that inhibition of migraine-related central sensitization could be an important new focus for future drug discovery, and may, for the first time, provide a rational target for the development of preventative medicines.
doi:10.1007/s10194-004-0120-7
PMCID: PMC3451579
Trigemino-vascular system; Migraine; Acute treatment; Prophylaxis; Pathophysiology
11.  New Insights into Pathophysiology of Vestibular Migraine 
Vestibular migraine (VM) is a common disorder in which genetic, epigenetic, and environmental factors probably contribute to its development. The pathophysiology of VM is unknown; nevertheless in the last few years, several studies are contributing to understand the neurophysiological pathways involved in VM. The current hypotheses are mostly based on the knowledge of migraine itself. The evidence of trigeminal innervation of the labyrinth vessels and the localization of vasoactive neuropeptides in the perivascular afferent terminals of these trigeminal fibers support the involvement of the trigemino-vascular system. The neurogenic inflammation triggered by activation of the trigeminal-vestibulocochlear reflex, with the subsequent inner ear plasma protein extravasation and the release of inflammatory mediators, can contribute to a sustained activation and sensitization of the trigeminal primary afferent neurons explaining VM symptoms. The reciprocal connections between brainstem vestibular nuclei and the structures that modulate trigeminal nociceptive inputs (rostral ventromedial medulla, ventrolateral periaqueductal gray, locus coeruleus, and nucleus raphe magnus) are critical to understand the pathophysiology of VM. Although cortical spreading depression can affect cortical areas involved in processing vestibular information, functional neuroimaging techniques suggest a dysmodulation in the multimodal sensory integration and processing of vestibular and nociceptive information, resulting from a vestibulo-thalamo-cortical dysfunction, as the pathogenic mechanism underlying VM. The elevated prevalence of VM suggests that multiple functional variants may confer a genetic susceptibility leading to a dysregulation of excitatory–inhibitory balance in brain structures involved in the processing of sensory information, vestibular inputs, and pain. The interactions among several functional and structural neural networks could explain the pathogenic mechanisms of VM.
doi:10.3389/fneur.2015.00012
PMCID: PMC4319397
migraine; aura; vertigo; multisensory integration; vestibulo-thalamo-cortical system; Meniere’s disease; vestibular system
12.  Favorable outcome of early treatment of new onset child and adolescent migraine-implications for disease modification 
The Journal of Headache and Pain  2009;10(4):227-233.
There is evidence that the prevalence of migraine in children and adolescents may be increasing. Current theories of migraine pathophysiology in adults suggest activation of central cortical and brainstem pathways in conjunction with the peripheral trigeminovascular system, which ultimately results in release of neuropeptides, facilitation of central pain pathways, neurogenic inflammation surrounding peripheral vessels, and vasodilatation. Although several risk factors for frequent episodic, chronic, and refractory migraine have been identified, the causes of migraine progression are not known. Migraine pathophysiology has not been fully evaluated in children. In this review, we will first discuss the evidence that early therapeutic interventions in the child or adolescent new onset migraineur, may halt or limit progression and disability. We will then review the evidence suggesting that many adults with chronic or refractory migraine developed their migraine as children or adolescents and may not have been treated adequately with migraine-specific therapy. Finally, we will show that early, appropriate and optimal treatment of migraine during childhood and adolescence may result in disease modification and prevent progression of this disease.
doi:10.1007/s10194-009-0133-3
PMCID: PMC3451739  PMID: 19506799
Disease modification; Child; Adolescent; Migraine
13.  Involvement of gap junction channels in the pathophysiology of migraine with aura 
Migraine is a common, recurrent, and disabling primary headache disorder with a genetic component which affects up to 20% of the population. One third of all patients with migraine experiences aura, a focal neurological disturbance that manifests itself as visual, sensitive or motor symptoms preceding the headache. In the pathophysiology of migraine with aura, activation of the trigeminovascular system from the meningeal vessels mediates migraine pain via the brainstem and projections ascend to the thalamus and cortex. Cortical spreading depression (CSD) was proposed to trigger migraine aura and to activate perivascular trigeminal nerves in the cortex. Quinine, quinidine and the derivative mefloquine are able to inhibit CSD suggesting an involvement of neuronal connexin36 channels in CSD propagation. More recently, CSD was shown to induce headache by activating the trigeminovascular system through the opening of stressed neuronal Pannexin1 channels. A novel benzopyran compound, tonabersat, was selected for clinical trial on the basis of its inhibitory activity on CSD and neurogenic inflammation in animal models of migraine. Interestingly, in the time course of animal model trials, tonabersat was shown to inhibit trigeminal ganglion (TGG) neuronal-glial cell gap junctions, suggesting that this compound could prevent peripheral sensitization within the ganglion. Three clinical trials aimed at investigating the effectiveness of tonabersat as a preventive drug were negative, and conflicting results were obtained in other trials concerning its ability to relieve attacks. In contrast, in another clinical trial, tonabersat showed a preventive effect on attacks of migraine with aura but had no efficacy on non-aura attacks. Gap junction channels seem to be involved in several ways in the pathophysiology of migraine with aura and emerge as a new promising putative target in treatment of this disorder.
doi:10.3389/fphys.2014.00078
PMCID: PMC3933780  PMID: 24611055
aura; connexin; cortical spreading depression; gap junction; pannexin; tonabersat; trigeminovascular
14.  Electrophysiological response patterns of primary sensory cortices in migraine 
The Journal of Headache and Pain  2006;7(6):377-388.
Migraine is an ictal disorder characterised by a particular vulnerability of patients to sensory overload, both during and outside of the attack. Central nervous system dysfunctions are supposed to play a pivotal role in migraine. Electroneurophysiological methods, which aim to investigate sensory processing, seem thus particularly appropriate to study the pathophysiology of migraine. We have thus reviewed evoked potential studies performed in migraine patients. Although results are in part contradictory, these studies nonetheless demonstrate an interictal dysfunction of sensory cortices, and possibly of subcortical structures, in migraine with and without aura. The predominant abnormality is a deficient habituation of evoked responses to repeated stimuli, probably due to cortical, and possibly widespread neural, "dysexcitability".
doi:10.1007/s10194-006-0343-x
PMCID: PMC3452223  PMID: 17164990
Migraine; Pathophysiology; Evoked potentials; Sensory cortices; Cortical excitability
15.  Migraine and estrogen 
Current opinion in neurology  2014;27(3):315-324.
Purpose of review
The aim is to systematically and critically review the relationship between migraine and estrogen, the predominant female sex hormone, with a focus on studies published in the last 18 months.
Recent findings
Recent functional MRI (fMRI) studies of the brain support the existence of anatomical and functional differences between men and women, as well as between participants with migraine and healthy controls. In addition to the naturally occurring changes in endogenous sex hormones over the lifespan (e.g. puberty and menopause), exogenous sex hormones (e.g. hormonal contraception or hormone therapy) also may modulate migraine. Recent data support the historical view of an elevated risk of migraine with significant drops in estrogen levels. In addition, several lines of research support that reducing the magnitude of decline in estrogen concentrations prevents menstrually related migraine (MRM) and migraine aura frequency.
Summary
Current literature has consistently demonstrated that headache, in particular migraine, is more prevalent in women as compared with men, specifically during reproductive years. Recent studies have found differences in headache characteristics, central nervous system anatomy, as well as functional activation by fMRI between the sexes in migraine patients. Although the cause underlying these differences is likely multifactorial, considerable evidence supports an important role for sex hormones. Recent studies continue to support that MRM is precipitated by drops in estrogen concentrations, and minimizing this decline may prevent these headaches. Limited data also suggest that specific regimens of combined hormone contraceptive use in MRM and migraine with aura may decrease both headache frequency and aura.
doi:10.1097/WCO.0000000000000091
PMCID: PMC4102139  PMID: 24792340
estradiol; estrogen; headache; migraine; sex hormone
16.  3D-Neuronavigation In Vivo Through a Patient's Brain During a Spontaneous Migraine Headache 
A growing body of research, generated primarily from MRI-based studies, shows that migraine appears to occur, and possibly endure, due to the alteration of specific neural processes in the central nervous system. However, information is lacking on the molecular impact of these changes, especially on the endogenous opioid system during migraine headaches, and neuronavigation through these changes has never been done. This study aimed to investigate, using a novel 3D immersive and interactive neuronavigation (3D-IIN) approach, the endogenous µ-opioid transmission in the brain during a migraine headache attack in vivo. This is arguably one of the most central neuromechanisms associated with pain regulation, affecting multiple elements of the pain experience and analgesia. A 36 year-old female, who has been suffering with migraine for 10 years, was scanned in the typical headache (ictal) and nonheadache (interictal) migraine phases using Positron Emission Tomography (PET) with the selective radiotracer [11C]carfentanil, which allowed us to measure µ-opioid receptor availability in the brain (non-displaceable binding potential - µOR BPND). The short-life radiotracer was produced by a cyclotron and chemical synthesis apparatus on campus located in close proximity to the imaging facility. Both PET scans, interictal and ictal, were scheduled during separate mid-late follicular phases of the patient's menstrual cycle. During the ictal PET session her spontaneous headache attack reached severe intensity levels; progressing to nausea and vomiting at the end of the scan session. There were reductions in µOR BPND in the pain-modulatory regions of the endogenous µ-opioid system during the ictal phase, including the cingulate cortex, nucleus accumbens (NAcc), thalamus (Thal), and periaqueductal gray matter (PAG); indicating that µORs were already occupied by endogenous opioids released in response to the ongoing pain. To our knowledge, this is the first time that changes in µOR BPND during a migraine headache attack have been neuronavigated using a novel 3D approach. This method allows for interactive research and educational exploration of a migraine attack in an actual patient's neuroimaging dataset.
doi:10.3791/50682
PMCID: PMC4186390  PMID: 24962460
Medicine; Issue 88; μ-opioid; opiate; migraine; headache; pain; Positron Emission Tomography; molecular neuroimaging; 3D; neuronavigation
17.  Genetics of migraine in the age of genome-wide association studies 
Genetic factors importantly contribute to migraine. However, unlike for rare monogenic forms of migraine, approaches to identify genes for common forms of migraine have been of limited success. Candidate gene association studies were often negative and positive results were often not replicated or replication failed. Further, the significance of positive results from linkage studies remains unclear owing to the inability to pinpoint the genes under the peaks that may be involved in migraine. Problems hampering these studies include limited sample sizes, methods of migraine ascertainment, and the heterogeneous clinical phenotype. Three genome-wide association studies are available now and have successfully identified four new genetic variants associated with migraine. One new variant (rs1835740) modulates glutamate homeostasis, thus integrates well with current concepts of neurotransmitter disturbances. This variant may be more specific for severe forms of migraine such as migraine with aura than migraine without aura. Another variant (rs11172113) implicates the lipoprotein receptor LRP1, which may interact with neuronal glutamate receptors, thus also providing a link to the glutamate pathway. In contrast, rs10166942 is in close proximity to TRPM8, which codes for a cold and pain sensor. For the first time this links a gene explicitly implicated in pain related pathways to migraine. The potential function of the fourth variant rs2651899 (PRDM16) in migraine is unclear. All these variants only confer a small to moderate change in risk for migraine, which concurs with migraine being a heterogeneous disorder. Ongoing large international collaborations will likely identify additional gene variants for migraine.
doi:10.1007/s10194-011-0399-0
PMCID: PMC3253157  PMID: 22072275
Migraine; Migraine with aura; Genetics; Genome-wide association studies; Glutamate; TRPM8; PRDM16; LRP1
18.  Genetics of migraine in the age of genome-wide association studies 
Genetic factors importantly contribute to migraine. However, unlike for rare monogenic forms of migraine, approaches to identify genes for common forms of migraine have been of limited success. Candidate gene association studies were often negative and positive results were often not replicated or replication failed. Further, the significance of positive results from linkage studies remains unclear owing to the inability to pinpoint the genes under the peaks that may be involved in migraine. Problems hampering these studies include limited sample sizes, methods of migraine ascertainment, and the heterogeneous clinical phenotype. Three genome-wide association studies are available now and have successfully identified four new genetic variants associated with migraine. One new variant (rs1835740) modulates glutamate homeostasis, thus integrates well with current concepts of neurotransmitter disturbances. This variant may be more specific for severe forms of migraine such as migraine with aura than migraine without aura. Another variant (rs11172113) implicates the lipoprotein receptor LRP1, which may interact with neuronal glutamate receptors, thus also providing a link to the glutamate pathway. In contrast, rs10166942 is in close proximity to TRPM8, which codes for a cold and pain sensor. For the first time this links a gene explicitly implicated in pain related pathways to migraine. The potential function of the fourth variant rs2651899 (PRDM16) in migraine is unclear. All these variants only confer a small to moderate change in risk for migraine, which concurs with migraine being a heterogeneous disorder. Ongoing large international collaborations will likely identify additional gene variants for migraine.
doi:10.1007/s10194-011-0399-0
PMCID: PMC3253157  PMID: 22072275
Migraine; Migraine with aura; Genetics; Genome-wide association studies; Glutamate; TRPM8; PRDM16; LRP1
19.  Hierarchical Alteration of Brain Structural and Functional Networks in Female Migraine Sufferers 
PLoS ONE  2012;7(12):e51250.
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.
doi:10.1371/journal.pone.0051250
PMCID: PMC3515541  PMID: 23227257
20.  Migraine Increases Centre-Surround Suppression for Drifting Visual Stimuli 
PLoS ONE  2011;6(4):e18211.
Background
The pathophysiology of migraine is incompletely understood, but evidence points to hyper-responsivity of cortical neurons being a key feature. The basis of hyper-responsiveness is not clear, with an excitability imbalance potentially arising from either reduced inhibition or increased excitation. In this study, we measure centre-surround contrast suppression in people with migraine as a perceptual analogue of the interplay between inhibition and excitation in cortical areas responsible for vision. We predicted that reduced inhibitory function in migraine would reduce perceptual surround suppression. Recent models of neuronal surround suppression incorporate excitatory feedback that drives surround inhibition. Consequently, an increase in excitation predicts an increase in perceptual surround suppression.
Methods and Findings
Twenty-six people with migraine and twenty approximately age- and gender-matched non-headache controls participated. The perceived contrast of a central sinusoidal grating patch (4 c/deg stationary grating, or 2 c/deg drifting at 2 deg/sec, 40% contrast) was measured in the presence and absence of a 95% contrast annular grating (same orientation, spatial frequency, and drift rate). For the static grating, similar surround suppression strength was present in control and migraine groups with the presence of the surround resulting in the central patch appearing to be 72% and 65% of its true contrast for control and migraine groups respectively (t(44) = 0.81, p = 0.42). For the drifting stimulus, the migraine group showed significantly increased surround suppression (t(44) = 2.86, p<0.01), with perceived contrast being on average 53% of actual contrast for the migraine group and 68% for non-headache controls.
Conclusions
In between migraines, when asymptomatic, visual surround suppression for drifting stimuli is greater in individuals with migraine than in controls. The data provides evidence for a behaviourally measurable imbalance in inhibitory and excitatory visual processes in migraine and is incompatible with a simple model of reduced cortical inhibitory function within the visual system.
doi:10.1371/journal.pone.0018211
PMCID: PMC3073931  PMID: 21494594
21.  New directions in migraine 
BMC Medicine  2011;9:116.
Migraine is a highly prevalent neurological disorder imparting a major burden on health care around the world. The primary pathology may be a state of hyperresponsiveness of the nervous system, but the molecular mechanisms are yet to be fully elucidated. We could now be at a watershed moment in this respect, as the genetic loci associated with typical forms of migraine are being revealed. The genetic discoveries are the latest step in the evolution of our understanding of migraine, which was initially considered a cerebrovascular condition, then a neuroinflammatory process and now primarily a neurogenic disorder. Indeed, the genetic findings, which have revealed ion channels and transporter mutations as causative of migraine, are a powerful argument for the neurogenic basis of migraine. Modulations of ion channels leading to amelioration of the migraine 'hyperresponsive' brain represent attractive targets for drug discovery. There lies ahead an exciting and rapidly progressing phase of migraine translational research, and in this review we highlight recent genetic findings and consider how these may affect the future of migraine neurobiology and therapy.
doi:10.1186/1741-7015-9-116
PMCID: PMC3217871  PMID: 22027350
22.  Migraine pathophysiology: anatomy of the trigeminovascular pathway and associated neurological symptoms, CSD, sensitization and modulation of pain 
Pain  2013;154 Suppl 1:10.1016/j.pain.2013.07.021.
Scientific evidence support the notion that migraine pathophysiology involves inherited alteration of brain excitability, intracranial arterial dilatation, recurrent activation and sensitization of the trigeminovascular pathway, and consequential structural and functional changes in genetically susceptible individuals. Evidence of altered brain excitability emerged from clinical and preclinical investigation of sensory auras, ictal and interictal hypersensitivity to visual, auditory and olfactory stimulation, and reduced activation of descending inhibitory pain pathways. Data supporting the activation and sensitization of the trigeminovascular system include the progressive development of cephalic and whole-body cutaneous allodynia during a migraine attack. Also, structural and functional alterations include the presence of subcortical white mater lesions, thickening of cortical areas involved in processing sensory information, and cortical neuroplastic changes induced by cortical spreading depression. Here, we review recent anatomical data on the trigeminovascular pathway and its activation by cortical spreading depression, a novel understanding of the neural substrate of migraine-type photophobia, and modulation of the trigeminovascular pathway by the brainstem, hypothalamus and cortex.
doi:10.1016/j.pain.2013.07.021
PMCID: PMC3858400  PMID: 24347803
23.  Possible sites of action of the new calcitonin gene-related peptide receptor antagonists 
Migraine is considered a neurovascular disease affecting more than 10% of the general population. Currently available drugs for the acute treatment of migraine are vasoconstrictors, which have limitations in their therapeutic use. The calcitonin gene-related peptide (CGRP) has a key role in migraine, where levels of CGRP are increased during acute migraine attacks. CGRP is expressed throughout the central and peripheral nervous system, consistent with control of vasodilatation and transmission of nociceptive information. In migraine, CGRP is released from the trigeminal system. At peripheral synapses CGRP results in vasodilatation via receptors on the smooth muscle cells. At central synapses, CGRP acts postjunctionally on second-order neurons to transmit pain centrally via the brainstem and midbrain to higher cortical pain regions. The recently developed CGRP-receptor antagonists have demonstrated clinical efficacy in the treatment of acute migraine attacks. A remaining question is their site of action. The CGRP-receptor components (calcitonin receptor-like receptor, receptor activity modifying protein 1 and receptor component protein) are found to colocalize in the smooth muscle cells of intracranial arteries and in large-sized neurons in the trigeminal ganglion. The CGRP receptor has also been localized within parts of the brain and the brainstem. The aim of this paper is to review recent localization studies of CGRP and its receptor components within the nervous system and to discuss whether these sites could be possible targets for the CGRP-receptor antagonists.
doi:10.1177/1756285610388343
PMCID: PMC3002638  PMID: 21179597
brainstem; calcitonin gene-related peptide; calcitonin gene-related peptide antagonists; migraine; trigeminal ganglion
24.  How Well Do Clinical Pain Assessment Tools Reflect Pain in Infants? 
PLoS Medicine  2008;5(6):e129.
Background
Pain in infancy is poorly understood, and medical staff often have difficulty assessing whether an infant is in pain. Current pain assessment tools rely on behavioural and physiological measures, such as change in facial expression, which may not accurately reflect pain experience. Our ability to measure cortical pain responses in young infants gives us the first opportunity to evaluate pain assessment tools with respect to the sensory input and establish whether the resultant pain scores reflect cortical pain processing.
Methods and Findings
Cortical haemodynamic activity was measured in infants, aged 25–43 wk postmenstrual, using near-infrared spectroscopy following a clinically required heel lance and compared to the magnitude of the premature infant pain profile (PIPP) score in the same infant to the same stimulus (n = 12, 33 test occasions). Overall, there was good correlation between the PIPP score and the level of cortical activity (regression coefficient = 0.72, 95% confidence interval [CI] limits 0.32–1.11, p = 0.001; correlation coefficient = 0.57). Of the different PIPP components, facial expression correlated best with cortical activity (regression coefficient = 1.26, 95% CI limits 0.84–1.67, p < 0.0001; correlation coefficient = 0.74) (n = 12, 33 test occasions). Cortical pain responses were still recorded in some infants who did not display a change in facial expression.
Conclusions
While painful stimulation generally evokes parallel cortical and behavioural responses in infants, pain may be processed at the cortical level without producing detectable behavioural changes. As a result, an infant with a low pain score based on behavioural assessment tools alone may not be pain free.
Rebeccah Slater and colleagues show that although painful stimulation generally evokes parallel cortical and behavioral responses in infants, pain may produce cortical responses without detectable behavioral changes.
Editors' Summary
Background.
Pain is a sensory and emotional experience. It is normally triggered by messages transmitted from specialized receptors (nociceptors) in the body to integrative centers in the spinal cord and brainstem and on to the brain, where it undergoes higher sensory and cognitive analysis, allowing the body to respond appropriately to the stimuli. While the experience of pain may be considered to be unpleasant, it is a useful tool in communicating to us and to others that there is something wrong with our bodies. Ultimately, these responses help restrict further damage to the body and start the process of healing.
In a clinical setting, the ability to communicate about pain allows an individual to seek strategies to ease the pain, such as taking analgesics. Being unable to effectively communicate one's experience of pain leaves the individual vulnerable to prolonged suffering. One such vulnerable group is infants.
Ignored and untreated pain in infants has been shown to have immediate and long-term effects as a result of structural and physiological changes within the nervous system. For example, the body responds to untreated pain by increased release of stress hormones, which may be associated with increased morbidity and mortality in the short term. Long-term effects of pain may include altered pain perception, chronic pain syndromes, and somatic complaints such as sleep disturbances, feeding problems, and inability to self-regulate in response to internal and external stressors. It has been proposed that attention deficit disorders, learning disorders, and behavioral problems in later childhood may be linked to repetitive pain in the preterm infant.
Why Was This Study Done?
Until as recently as the 1990s, newborns in some clinical centres underwent surgery with minimal anesthesia. Also, newborns received little or no pain management postoperatively or for painful procedures such as lumbar punctures or circumcisions. Since then, there has been growing awareness amongst clinicians that pain may be experienced from the earliest stages of postnatal life and that inadequate analgesia may lead to the type of long-term consequences mentioned above. However, gauging how much pain infants and young children are experiencing remains a substantial challenge. The researchers in this study wanted to assess the association between cortical pain responses in young infants and currently used tools for the assessment of pain in these infants. These current tools are based on behavioral and physiological measures, such as change in facial expression, and it is possible that these tools do not give an adequate measure of pain especially in infants born preterm.
What Did the Researchers Do and Find?
Twelve clinically stable infants were studied on 33 occasions when they required a heel lance to obtain a blood sample for a clinical reason. The researchers examined the relationship between brain activity and a clinical pain score, calculated using the premature infant pain profile (PIPP) in response to a painful event. Activity in the somatosensory cortex was measured noninvasively by near-infrared spectroscopy, which measures brain regional changes in oxygenated and deoxygenated hemoglobin concentration. The PIPP is a well-established pain score that ascribes a value to infant behavior such as change in facial expression.
They found that changes in brain activity in response to a painful stimulus were related to the PIPP scores. These changes were more strongly linked to the behavioral components of the PIPP, e.g., facial expression, than physiological components, e.g., heart rate. They also found that a positive brain response could occur in the absence of any facial expression.
What Do These Findings Mean?
Behaviors to communicate pain require motor responses to sensory and emotional stimuli. The maturity of this complex system in infants is not clearly understood. The results of this study raise further awareness of the ability of infants to experience pain and highlight the possibility that pain assessment based on behavioral tools alone may underestimate the pain response in infants.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050129.
Important papers on pain in human neonates are discussed in the open access Paediatric Pain Letter with links to original articles
The Institute of Child Health in London has a Web site describing a three-year international project on improving the assessment of pain in hospitalized children, with many useful links
The International Association for the Study of Pain (IASP) provides accurate and up-to-date information and links about pain mechanisms and treatment
doi:10.1371/journal.pmed.0050129
PMCID: PMC2504041  PMID: 18578562
25.  Habituation and sensitization in primary headaches 
The phenomena of habituation and sensitization are considered most useful for studying the neuronal substrates of information processing in the CNS. Both were studied in primary headaches, that are functional disorders of the brain characterized by an abnormal responsivity to any kind of incoming innocuous or painful stimuli and it’s cycling pattern over time (interictal, pre-ictal, ictal). The present review summarizes available data on stimulus responsivity in primary headaches obtained with clinical neurophysiology. In migraine, the majority of electrophysiological studies between attacks have shown that, for a number of different sensory modalities, the brain is characterised by a lack of habituation of evoked responses to repeated stimuli. This abnormal processing of the incoming information reaches its maximum a few days before the beginning of an attack, and normalizes during the attack, at a time when sensitization may also manifest itself. An abnormal rhythmic activity between thalamus and cortex, namely thalamocortical dysrhythmia, may be the pathophysiological mechanism subtending abnormal information processing in migraine. In tension-type headache (TTH), only few signs of deficient habituation were observed only in subgroups of patients. By contrast, using grand-average responses indirect evidence for sensitization has been found in chronic TTH with increased nociceptive specific reflexes and evoked potentials. Generalized increased sensitivity to pain (lower thresholds and increased pain rating) and a dysfunction in supraspinal descending pain control systems may contribute to the development and/or maintenance of central sensitization in chronic TTH. Cluster headache patients are chrarcterized during the bout and on the headache side by a pronounced lack of habituation of the brainstem blink reflex and a general sensitization of pain processing. A better insight into the nature of these ictal/interictal electrophysiological dysfunctions in primary headaches paves the way for novel therapeutic targets and may allow a better understanding of the mode of action of available therapies.
doi:10.1186/1129-2377-14-65
PMCID: PMC3733593  PMID: 23899115
Migraine; Tension-type headache; Cluster headache; Trigeminal autonomic cephalalgias; Sensitization; Habituation; Evoked potentials; Reflex; Pain mechanisms; Thalamocortical dysrhythmia

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