Trigeminal nociceptive transmission in migraineurs predicts migraine attacks

The migraine generator revisited: continuous scanning of the migraine cycle over 30 days and three spontaneous attacks

Functional imaging using positron emission tomography and later functional magnetic resonance imaging revealed a particular brainstem area that is believed to be specifically activated in migraine during, but not outside of the attack, and consequently has been coined the 'migraine generator'. However, the pathophysiological concept behind this term is not undisputed and typical migraine premonitory symptoms such as fatigue and yawning, but also a typical association of attacks to circadian and menstrual cycles, all make the hypothalamus a possible regulating region of migraine attacks. Neuroimaging studies investigating native human migraine attacks however are scarce and for methodological but also clinical reasons there are currently no studies investigating the last 24 h before headache onset. Here we report a migraine patient who had magnetic resonance imaging every day for 30 days, always in the morning, to cover, using functional imaging, a whole month and three complete, untreated migraine attacks. We found that hypothalamic activity as a response to trigeminal nociceptive stimulation is altered during the 24 h prior to pain onset, i.e. increases towards the next migraine attack. More importantly, the hypothalamus shows altered functional coupling with the spinal trigeminal nuclei and the region of the migraine generator, i.e. the dorsal rostral pons during the preictal day and the pain phase of native human migraine attacks. These data suggest that although the brainstem is highly linked to the migraine biology, the real driver of attacks might be the functional changes in hypothalamo-brainstem connectivity.

The surgical management of cephalalgia

PURPOSE OF REVIEW

Management of headache disorders is not part of most craniomaxillofacial surgery practices; however there are certain indications for surgical management of headaches by the craniomaxillofacial surgeon.

RECENT FINDINGS

Migraine headaches are the most amenable to surgical management and while the exact mechanism of migraine is unknown, a central or peripheral trigger such as compressive neuropathy of trigeminal nerve branches leading to neurogenic inflammation has been suggested. The primary management for episodic migraine headache should be lifestyle modification and medication, whereas for chronic migraine (>15 headache days/month) use of medication and botulinum neurotoxin is effective, whereas some patients may choose to explore surgical options. Trigger site decompression for chronic migraine surgically relieves anatomic impingement at various sites and has been shown to reduce by at least 50% the frequency, intensity, and duration of headaches in over 85% and elimination of headaches in almost 60%. Trigger points may also lead to exacerbation of cluster headaches and treatment with botulinum neurotoxin may reduce attacks.

SUMMARY

Trigger site decompression is an effective treatment for chronic migraine, as are botulinum neurotoxin injections in reducing attacks in cluster headaches. The craniomaxillofacial surgeon is uniquely qualified to treat these primary headache disorders.

Functional imaging and migraine: new connections?

PURPOSE OF REVIEW

Over the last several years, a growing number of brain functional imaging studies have provided insights into mechanisms underlying migraine. This article reviews the recent migraine functional neuroimaging literature and provides recommendations for future studies that will help fill knowledge gaps.

RECENT FINDINGS

PET and functional MRI studies have identified brain regions that might be responsible for mediating the onset of a migraine attack and those associated with migraine symptoms. Enhanced activation of brain regions that facilitate processing of sensory stimuli suggests a mechanism by which migraineurs are hypersensitive to visual, olfactory, and cutaneous stimuli. Resting state functional connectivity MRI studies have identified numerous brain regions and functional networks with atypical functional connectivity in migraineurs, suggesting that migraine is associated with aberrant brain functional organization.

SUMMARY

Functional MRI and PET studies that have identified brain regions and brain networks that are atypical in migraine have helped to describe the neurofunctional basis for migraine symptoms. Future studies should compare functional imaging findings in migraine to other headache and pain disorders and should explore the utility of functional imaging data as biomarkers for diagnostic and treatment purposes.

Trigeminal somatosensorial evoked potentials suggest increased excitability during interictal period in patients with long disease duration in migraine

INTRODUCTION

Migraine pathogenesis is suggested to involve many structures in cerebral cortex, brainstem and trigeminovascular system. Electrophysiological studies revealed loss of habituation, decreased cortical preactivation, segmental hypersensitivity and reduction in control of inhibitory descending pathways. Given these information, we aimed to evaluate the excitability changes of the trigeminal pathway in the cortex and brainstem in migraine using trigeminal nerve somatosensory evoked potentials (TSEP).

PATIENTS AND METHOD

Fifty-one women with migraine without aura and 32 age-matched healthy women were included. TSEPs were recorded in migraine patients during interictal period and in healthy subjects. Sensory thresholds, stimulation intensities, latencies of N1, P1, N2 and P2 waves as well as N1/P1 and N2/P1 amplitudes were measured.

RESULTS

Comparisons of ipsilateral latencies with N1-P1 and N2-P1 amplitudes between migraine and control groups showed no difference. Sensory thresholds were also similar. Stimulation thresholds decreased as the attack frequency increased and ipsilateral N1/P1 amplitude increased with prolonged disease duration (p=0.043).

CONCLUSION

Our study did not show significant difference between migraine patients and healthy subjects during interictal period. However, migraine with long duration affects the excitability of the cortical and brainstem trigeminal pathways even during interictal periods.

Hypoechogenicity of brainstem raphe nuclei is associated with increased attack frequency in episodic migraine

INTRODUCTION

Reduced echogenicity of the brainstem raphe nuclei (BRN) was demonstrated in major depression, possibly indicating serotonergic dysfunction. Postulating that migraine may constitute a "chronic low serotonin syndrome," we aimed to evaluate the echogenicity of midbrain structures, including serotonergic BRN in episodic migraine.

METHODS

Transcranial sonography was performed in 39 patients with episodic migraine (median age 35, interquartile range (IQR): 27-47 years; 27 women) and 35 controls (median age 31, IQR: 29-47 years; 19 women). Individuals with concomitant depression were excluded. Echogenicity of BRN, substantia nigra (SN) and third ventricle width was evaluated according to an internationally established examination protocol.

RESULTS

Hypoechogenicity of BRN was depicted in 23.1% of migraine patients and 20% of controls, showing no significant difference. Migraine patients with hypoechogenic BRN had significantly higher attack frequency (median 3, IQR 2-5 vs. 1.5, IQR 1-2 days/month; p = 0.029) and a trend toward earlier disease manifestation. The rate of hyperechogenic SN and width of the third ventricle were similar between both groups. We did not observe any differences between migraine patients with and without aura.

CONCLUSION

Sonographic findings did not differ between migraine patients and controls. Hypoechogenic BRN correlated to a higher migraine attack frequency, probably indicating more severe disease activity.

Lateral inhibition in the somatosensory cortex during and between migraine without aura attacks: Correlations with thalamocortical activity and clinical features

Background

We studied lateral inhibition in the somatosensory cortex of migraineurs during and between attacks, and searched for correlations with thalamocortical activity and clinical features.

Participants and methods

Somatosensory evoked potentials (SSEP) were obtained by electrical stimulation of the right median (M) or ulnar (U) nerves at the wrist or by simultaneous stimulation of both nerves (MU) in 41 migraine without aura patients, 24 between (MO), 17 during attacks, and in 17 healthy volunteers (HVs). We determined the percentage of lateral inhibition of the N20–P25 component by using the formula [(100)–MU/(M + U)*100]. We also studied high-frequency oscillations (HFOs) reflecting thalamocortical activation.

Results

In migraine, both lateral inhibition (MO 27.9% vs HVs 40.2%; p = 0.009) and thalamocortical activity (MO 0.5 vs HVs 0.7; p = 0.02) were reduced between attacks, but not during. In MO patients, the percentage of lateral inhibition negatively correlated with days elapsed since the last migraine attack ( r = −0.510, p = 0.01), monthly attack duration ( r = −0.469, p = 0.02) and severity ( r = −0.443, p = 0.03), but positively with thalamocortical activity ( r = −0.463, p = 0.02).

Conclusions

We hypothesize that abnormal migraine cycle-dependent dynamics of connectivity between subcortical and cortical excitation/inhibition networks may contribute to clinical features of MO and recurrence of attacks.

Responsiveness of the autonomic nervous system during paced breathing and mental stress in migraine patients

Background

Migraine is a stress-related disorder, suggesting that there may be sympathetic hyperactivity in migraine patients. However, there are contradictory results concerning general sympathetic activation in migraine patients. To shed more light on the involvement of the autonomic nervous system (ANS) in migraine pathophysiology, we investigated cardiac and cardiovascular reactions during vagal (paced breathing) and sympathetic activation (mental stress test).

Methods

Heart rate variability parameters and skin conductance responses were recorded interictally in 22 episodic migraine patients without aura and 25 matched controls during two different test conditions. The paced breathing test consisted of a five-minute baseline, followed by two minutes of paced breathing (6 breathing cycles per minute) and a five-minute recovery phase. The mental stress test consisted of a five-minute baseline, followed by one minute of stress anticipation, three and a half minutes of mental stress and a five-minute recovery phase. Furthermore we measured blood pressure and heart rate once daily over 2 weeks. Subjects rated their individual current stress level and their stress level during paced breathing and during the mental stress test.

Results

There were no significant differences between migraine patients and controls in any of the heart rate variability parameters in either time domain or frequency domain analysis. However, all parameters showed a non-significant tendency for larger sympathetic activation in migraine patients. Also, no significant differences could be observed in skin conductance responses and average blood pressure. Only heart rates during the 2-week period and stress ratings showed significantly higher values in migraine patients compared to controls.

Conclusions

Generally there were no significant differences between migraine patients and controls concerning the measured autonomic parameters. There was a slight but not significant tendency in the migraine patients to react with less vagal and more sympathetic activation in all these tests, indicating a slightly changed set point of the autonomic system. Heart rate variability and blood pressure in migraine patients should be investigated for longer periods and during more demanding sympathetic activation.

Central Nervous System Underpinnings of Sensory Hypersensitivity in Migraine: Insights from Neuroimaging and Electrophysiological Studies

Whereas considerable data have been generated about the pathophysiology of pain processing during migraine attacks, relatively little is known about the neural basis of sensory hypersensitivity. In migraine, the term "hypersensitivity" encompasses different and probably distinct pathophysiological aspects of sensory sensitivity. During attacks, many patients have enhanced sensitivity to visual, auditory and/or olfactory stimuli, which can enhance headache while interictally, migraineurs often report abnormal sensitivity to environmental stimuli that can cause nonpainful discomfort. In addition, sensorial stimuli can influence and trigger the onset of migraine attacks. The pathophysiological mechanisms and the origin of such sensitivity (individual predisposition to develop migraine disease or consequence of repeated migraine attacks) are ill understood. Functional neuroimaging and electrophysiological studies allow for noninvasive measures of neuronal responses to external stimuli and have contributed to our understanding of mechanisms underlying sensory hypersensitivity in migraine. The purpose of this review is to present pivotal neuroimaging and neurophysiological studies that explored the basal state of brain responsiveness to sensory stimuli in migraineurs, the alterations in habituation and attention to sensory inputs, the fluctuations of responsiveness to sensory stimuli before and during migraine attacks, and the relations between sensory hypersensitivity and clinical sensory complaints.

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.

Localization of CGRP receptor components and receptor binding sites in rhesus monkey brainstem: A detailed study using in situ hybridization, immunofluorescence, and autoradiography

Functional imaging studies have revealed that certain brainstem areas are activated during migraine attacks. The neuropeptide calcitonin gene-related peptide (CGRP) is associated with activation of the trigeminovascular system and transmission of nociceptive information and plays a key role in migraine pathophysiology. Therefore, to elucidate the role of CGRP, it is critical to identify the regions within the brainstem that process CGRP signaling. In situ hybridization and immunofluorescence were performed to detect mRNA expression and define cellular localization of calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1), respectively. To define CGRP receptor binding sites, in vitro autoradiography was performed with [(3)H]MK-3207 (a CGRP receptor antagonist). CLR and RAMP1 mRNA and protein expression were detected in the pineal gland, medial mammillary nucleus, median eminence, infundibular stem, periaqueductal gray, area postrema, pontine raphe nucleus, gracile nucleus, spinal trigeminal nucleus, and spinal cord. RAMP1 mRNA expression was also detected in the posterior hypothalamic area, trochlear nucleus, dorsal raphe nucleus, medial lemniscus, pontine nuclei, vagus nerve, inferior olive, abducens nucleus, and motor trigeminal nucleus; protein coexpression of CLR and RAMP1 was observed in these areas via immunofluorescence. [(3)H]MK-3207 showed high binding densities concordant with mRNA and protein expression. The present study suggests that several regions in the brainstem may be involved in CGRP signaling. Interestingly, we found receptor expression and antagonist binding in some areas that are not protected by the blood-brain barrier, which suggests that drugs inhibiting CGRP signaling may not be able to penetrate the central nervous system to antagonize receptors in these brain regions.

Laser-evoked potential habituation and central sensitization symptoms in childhood migraine

Objectives

Few studies have addressed central sensitization symptoms and pain processing in childhood migraine. Our aims were to examine pain sensitivity and responses, including habituation, evoked by CO2 laser stimuli (laser-evoked potentials (LEPs)) in a cohort of children with migraine compared to non-migraine controls and to determine the correlation between LEP features and signs of central sensitization.

Methods

Thirty-five patients 8–15 years of age with migraines without aura were evaluated during the inter-critical phase and were compared to 17 controls. LEPs were analyzed, and their main features were correlated with clinical symptoms including allodynia and pericranial tenderness.

Results

The laser-evoked pain threshold was lower and the N2P2 vertex complex amplitude was higher in children with migraines. Furthermore, habituation of vertex waves of LEPs clearly showed a tendency toward progressive amplitude enhancement in the migraine group. Acute allodynia and inter-critical pericranial tenderness correlated with trigeminal LEP features, particularly with the abnormal habituation pattern.

Discussion

Abnormalities of pain processing and symptoms of central sensitization appear to be characteristics of children with migraine. Reduced habituation and progressive amplification of cortical responses to laser stimuli indicate an overactive nociceptive system at the onset of migraine, and this hyperactivity may subtend allodynia and pericranial tenderness. Future prospective trials may aid in the early identification of clinical phenotypes that display a tendency to develop into the chronic form of migraine, warranting a timely therapeutic approach.

The estrous cycle modulates voltage-gated ion channels in trigeminal ganglion neurons

Migraines typically occur more frequently in women than men because of the effects of estrogen on both the frequency and severity of migraine attacks. Many women suffer from migraine attacks during menstruation, which are known as menstrual migraines. The pathophysiology of menstrual migraines can be explored by using the rat estrous cycle, which shows a cyclical fluctuation of estrogen level that resembles the menstrual cycle. The aim of this study was to investigate whether different stages of the estrous cycle are involved in migraine development by comparing the excitability of trigeminal ganglion (TG) neurons in four different stages of the estrous cycle by using action potential (AP) parameter assessments. The stages of the estrous cycle were identified by a vaginal smear and measuring the estrogen levels in collected blood. The proestrus and estrus stages had higher estrogen levels compared with the diestrus and metestrus stages. Whole-cell patch clamp recordings demonstrated that TG neurons in the proestrus and estrus stage had lower AP threshold, lower rheobase, higher AP height, shorter AP falling time and deeper afterhyperpolarization (AHP) depth. Hence, our results revealed that the high level of estrogen in the proestrus and estrus stage alters the AP properties of TG neurons. Estrogen may increase membrane excitability and the summation of cellular responses, which alters the AP properties. The alterations of the AP properties in the proestrus and estrus stage may relate to a modification of voltage-gated ion channels in TG neurons, which is a pathogenesis for menstrual migraine. No COI.

Photo-, osmo- and phonophobia in the premonitory phase of migraine: mistaking symptoms for triggers?

Background

Certain environmental stimuli are frequently reported as typical triggers of migraine pain. Whether these so-called triggers are independent precipitators of migraine pain or mere symptoms of the premonitory phase of migraine remains to be elucidated.

Methods

In this retrospective cohort study of 1010 migraine patients of a tertiary headache center we assessed the frequency of common trigger factors, premonitory symptoms and accompanying symptoms as well as basic headache characteristics and demographic data.

Results

Premonitory symptoms with an onset of 2 or more hours prior to the headache were present in 38.9% of migraine patients, the most frequent being a tense neck, phonophobia and difficulty concentrating. There was a clear overlap of certain trigger factors and the presence of corresponding premonitory symptoms: flickering or bright light as a trigger was associated with higher frequency of photophobia in the premonitory phase. The same applied to the presence of food craving and osmophobia in the premonitory phase and certain foods or odours as trigger factors.

Conclusions

Our data thus support the view that commonly reported trigger factors of migraine are not so much independent precipitators of migraine pain, but that they are most likely just misinterpreted results of enhanced attention to certain stimuli mediated by typical premonitory symptoms of migraine pain.

No microstructural white matter alterations in chronic and episodic migraineurs: a case-control diffusion tensor magnetic resonance imaging study

BACKGROUND

In patients with episodic migraine (EM), diffusion tensor imaging (DTI) revealed microstructural white matter alterations in various brain regions related to pain processing. Some of these changes were correlated with migraine duration and attack frequency, suggesting that migraine is a progressive disease with proceeding structural alterations of the brain. This study aimed to identify possible microstructural white matter alterations in patients with chronic migraine (CM) using DTI. We hypothesized that alterations in DTI are more pronounced in patients with CM compared with EM.

METHODS

Individually, age- and sex-matched subjects with CM without aura, EM without aura, and healthy controls (n = 21 per group) underwent conventional head magnetic resonance imaging and DTI imaging in a 3T MRI scanner and were included in analysis. DTI data were analyzed using a tract-based spatial statistics approach. Fractional anisotropy (FA), mean diffusivity, radial diffusivity, and axial diffusivity were compared between subjects with CM and EM, CM and controls, EM and controls, as well as between all subjects with migraine (EM + CM) and controls.

RESULTS

In chronic migraineurs (mean age 49 ± 7.5 years), we did not find any statistically significant difference (P < .05, threshold-free cluster enhancement corrected for multiple comparison) in DTI-derived parameters in comparison with episodic migraineurs (FA: P > .245) and healthy controls (FA: P > .099). In contrast to previous DTI studies, we did not find alterations in DTI-derived indices in subjects with EM compared with healthy controls (FA: P > .486).

CONCLUSIONS

No microstructural white matter changes could be observed in middle-aged chronic and episodic migraineurs using DTI. CM does not seem to be a risk factor for progressive microstructural changes in DTI.

Functional MRI of migraine

Migraine is a disabling neurological condition manifesting with attacks of headache, hypersensitivities to visual, auditory, olfactory and somatosensory stimuli, nausea, and vomiting. Exposure to sensory stimuli, such as odours, visual stimuli, and sounds, commonly triggers migraine attacks, and hypersensitivities to sensory stimuli are prominent during migraine attacks, but can persist with less magnitude between attacks. Functional MRI (fMRI) has been used to investigate the mechanisms that lead to migraine sensory hypersensitivities by measuring brain responses to visual, olfactory, and painful cutaneous stimulation, and functional connectivity analyses have investigated the functional organisation of specific brain regions and networks responsible for sensory processing. These studies have consistently shown atypical brain responses to sensory stimuli, absence of the normal habituating response between attacks, and atypical functional connectivity of sensory processing regions. Identification of the mechanisms that lead to migraine sensory hypersensitivities and that trigger migraine attacks in response to sensory stimuli might help to better understand neural dysfunction in migraine and provide new targets for migraine prevention, and could provide fMRI biomarkers that indicate early responses to preventive therapy.

Understanding migraine using dynamic network biomarkers

Background

Mathematical modeling approaches are becoming ever more established in clinical neuroscience. They provide insight that is key to understanding complex interactions of network phenomena, in general, and interactions within the migraine-generator network, in particular.

Purpose

In this study, two recent modeling studies on migraine are set in the context of premonitory symptoms that are easy to confuse for trigger factors. This causality confusion is explained, if migraine attacks are initiated by a transition caused by a tipping point.

Conclusion

We need to characterize the involved neuronal and autonomic subnetworks and their connections during all parts of the migraine cycle if we are ever to understand migraine. We predict that mathematical models have the potential to dismantle large and correlated fluctuations in such subnetworks as a dynamic network biomarker of migraine.

Central effects of acetylsalicylic acid on trigeminal-nociceptive stimuli

BACKGROUND

Acetylsalicylic acid is one of the most used analgesics to treat an acute migraine attack. Next to the inhibitory effects on peripheral prostaglandin synthesis, central mechanisms of action have also been discussed.

METHODS

Using a standardized model for trigeminal-nociceptive stimulation during fMRI scanning, we investigated the effect of acetylsalicylic acid on acute pain compared to saline in 22 healthy volunteers in a double-blind within-subject design. Painful stimulation was applied using gaseous ammonia and presented in a pseudo-randomized order with several control stimuli. All participants were instructed to rate the intensity and unpleasantness of every stimulus on a VAS scale. Based on previous results, we hypothesized to find an effect of ASA on central pain processing structures like the ACC, SI and SII as well as the trigeminal nuclei and the hypothalamus.

RESULTS

Even though we did not find any differences in pain ratings between saline and ASA, we observed decreased BOLD signal changes in response to trigemino-nociceptive stimulation in the ACC and SII after administration of ASA compared to saline. This finding is in line with earlier imaging results investigating the effect of ASA on acute pain. Contrary to earlier findings from animal studies, we could not find an effect of ASA on the trigeminal nuclei in the brainstem or within the hypothalamic area.

CONCLUSION

Taken together our study replicates earlier findings of an attenuating effect of ASA on pain processing structures, which adds further evidence to a possibly central mechanism of action of ASA.

Chaos and commotion in the wake of cortical spreading depression and spreading depolarizations

Punctuated episodes of spreading depolarizations erupt in the brain, encumbering tissue structure and function, and raising fascinating unanswered questions concerning their initiation and propagation. Linked to migraine aura and headache, cortical spreading depression contributes to the morbidity in the world's migraine with aura population. Even more ominously, erupting spreading depolarizations accelerate tissue damage during brain injury. The once-held view that spreading depolarizations may not exist in the human brain has changed, largely because of the discovery of migraine genes that confer cortical spreading depression susceptibility, the application of sophisticated imaging tools and efforts to interrogate their impact in the acutely injured human brain.

μ-Opioid activation in the midbrain during migraine allodynia - brief report II

We investigated in vivo the allodynic response of the central μ-opioid system during spontaneous migraine headaches, following a sustained pain threshold challenge on the trigeminal ophthalmic region. Six migraineurs were scanned during the ictal and interictal phases using positron emission tomography (PET) with the selective μ-opioid receptor (μOR) radiotracer [11C]carfentanil. Females were scanned during the mid-late follicular phase of two separate cycles. Patients showed ictal trigeminal allodynia during the thermal challenge that was concurrent and positively correlated with μOR activation in the midbrain, extending from red nucleus to ventrolateral periaqueductal gray matter. These findings demonstrate for the first time in vivo the high μOR activation in the migraineurs' brains in response to their allodynic experience.

Is the migrainous brain normal outside of acute attacks? Lessons learned from psychophysical, neurochemical and functional neuroimaging studies

Migraine is a largely inherited disorder of the brain with recurrent head pain attacks. There is an increasing awareness, however, that the manifestation of migrainous biology is not restricted to such acute head pain attacks, but that migraine is rather a disorder with a continuous complex and broad sensory processing dysfunction in which normal sensory stimuli (somatosensory, visual, auditory and olfactory) are misinterpreted by the brain. This dysfunction is most prominent during attacks, but there are more and more evidences that the processing and perception of stimuli is abnormal also outside of attacks to a varying degree. In this topical review, we will summarize and discuss the current clinical, neurochemical and functional neuroimaging literature on this paradigm shift from a strictly episodic head pain disorder to migraine as a more general dysfunction of sensory processing.

Altered hypothalamic functional connectivity with autonomic circuits and the locus coeruleus in migraine

The hypothalamus has been implicated in migraine based on the manifestation of autonomic symptoms with the disease, as well as neuroimaging evidence of hypothalamic activation during attacks. Our objective was to determine functional connectivity (FC) changes between the hypothalamus and the rest of the brain in migraine patients vs. control subjects. This study uses fMRI (functional magnetic resonance imaging) to acquire resting state scans in 12 interictal migraine patients and 12 healthy matched controls. Hypothalamic connectivity seeds were anatomically defined based on high-resolution structural scans, and FC was assessed in the resting state scans. Migraine patients had increased hypothalamic FC with a number of brain regions involved in regulation of autonomic functions, including the locus coeruleus, caudate, parahippocampal gyrus, cerebellum, and the temporal pole. Stronger functional connections between the hypothalamus and brain areas that regulate sympathetic and parasympathetic functions may explain some of the hypothalamic-mediated autonomic symptoms that accompany or precede migraine attacks.

The role of BOLD-fMRI in elucidating migraine pathophysiology

Migraine is a neurologic disorder characterized by disabling attacks of throbbing headache with specific features and associated symptoms. Despite the recent discoveries in basic neurosciences, migraine pathophysiology is not completely understood. Nevertheless, in the last decades, advances in functional magnetic resonance imaging (fMRI) have significantly provided new insights into migraine mechanisms. Blood oxygen level dependent (BOLD) fMRI technique is the most commonly used method to explore brain function and connectivity due to high temporal and spatial resolution. The purpose of this review is to present a synthesis of recent BOLD-fMRI studies which have allowed us to elucidate the complex process involved in migraine pathophysiology.

Migraine pathophysiology: anatomy of the trigeminovascular pathway and associated neurological symptoms, CSD, sensitization and modulation of pain

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.

Differential brain activity in subjects with painful trigeminal neuropathy and painful temporomandibular disorder

Human brain imaging investigations have revealed that acute pain is associated with coactivation of numerous brain regions, including the thalamus, somatosensory, insular, and cingulate cortices. Surprisingly, a similar set of brain structures is not activated in all chronic pain conditions, particularly chronic neuropathic pain, which is associated with almost exclusively decreased thalamic activity. These inconsistencies may reflect technical issues or fundamental differences in the processing of acute compared with chronic pain. The appreciation of any differences is important because better treatment development will depend on understanding the underlying mechanisms of different forms of pain. In this investigation, we used quantitative arterial spin labeling to compare and contrast regional cerebral blood flow (CBF) patterns in individuals with chronic neuropathic orofacial pain (painful trigeminal neuropathy) and chronic nonneuropathic orofacial pain (painful temporomandibular disorder). Neuropathic pain was associated with CBF decreases in a number of regions, including the thalamus and primary somatosensory and cerebellar cortices. In contrast, chronic nonneuropathic pain was associated with significant CBF increases in regions commonly associated with higher-order cognitive and emotional functions, such as the anterior cingulate and dorsolateral prefrontal cortices and the precuneus. Furthermore, in subjects with nonneuropathic pain, blood flow increased in motor-related regions as well as within the spinal trigeminal nucleus.

Relevance of functional neuroimaging studies for understanding migraine mechanisms

Advances in imaging have provided further insights into the complex migraine pathophysiology. Functional neuroimaging by means of PET and functional MRI studies have addressed crucial migraine-related issues, improving our understanding of the circuitry that may be involved in the generation, maintenance and recurrence of pain symptoms in migraine. In the last few years, a growing body of imaging literature has also explored pathophysiology of associated migraine symptoms. Of great interest will be the use of advanced imaging techniques to elucidate neural correlates of migraine prodromal, in order to identify clinical subgroups of migrainous subjects. However, the interpretation of the biological significance of these various functional changes could remain incomplete without a combination of expanding genomic information about neurochemical pathways and genetic polymorphisms linked to specific migraine subtypes. Hopefully, a more detailed picture of the migraine neurobiology will emerge from future neuroimaging studies, which may eventually lead to better and more rational treatments.

Pearls and pitfalls: Neuroimaging in headache

Premise

One of the most exciting developments in modern neuroscience was the development of imaging techniques providing a non-invasive technique for detection of structure-function relationships characteristic of pain and headache. There is no question that neuroimaging has provided us with a better understanding of how the aura in migraine develops, and it has served as a bridge between neurophysiological studies and clinical findings, although doubtless several questions remain.

Pearls

Neuroimaging drew attention toward central mechanisms in idiopathic headache syndromes. Outstanding functional studies have reinforced the crucial role of the brainstem in acute and chronic migraine and the hypothalamic area in trigemino-autonomic headaches. Several morphometric studies suggest a decreased gray matter in pain-transmitting areas in headache patients; however, those have to be seen in the light of a wealth of pain studies and studies on exercise-dependent plasticity.

Goal

This review focuses on neuroimaging as a scientific tool and highlights the recent advances made in studying primary headache syndromes using functional and structural neuroimaging techniques. It will also point toward open questions and gives recommendations for future studies.

Functional neuroimaging of migraine

This review summarizes the history of migraine imaging and key findings of studies on functional neuroimaging in migraine and describes how these data have changed our view of the disorder. Functional neuroimaging during migraine attacks and also interictally has initiated the description of "the migraine brain". These studies have led to the demonstration of cortical spreading depression in migraine with aura, the crucial role for the brainstem during migraine attacks, and cortical hypersensitivity in migraineurs modulated by the trigeminal pathway, explaining sensory sensitization such as photophobia and osmophobia.

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.

Neuronal correlates of impaired habituation in response to repeated trigemino-nociceptive but not to olfactory input in migraineurs: An fMRI study

Introduction:

Using functional magnetic resonance imaging (fMRI), we aimed to explore the habituation behaviour to trigemino-nociceptive as well as olfactory stimuli in migraine patients. We exclusively focussed on intrasessional behavioural rating patterns and the related blood oxygen level dependent (BOLD) signal changes.

Findings:

We observed that groups significantly differ in the time course of pain intensity ratings during the stimulation session: whereas interictal migraineurs sensitized (increasing pain ratings), control subjects habituated (decreasing pain ratings). Pain ratings of ictal patients remained unchanged. This behaviour is accompanied by a similar time course of neuronal activity in the bilateral anterior insula, in the middle cingulate cortex and in the thalamus. In these areas, the brain activity increased in migraineurs but decreased in the control group during the session. In contrast to these findings, the rating patterns for the olfactory stimuli (rose odour) did not differ between patients and controls and a gradual decrease of perceived stimulus intensity was found in all three groups. This stimulus specific response may occur because the olfactory system is the only sensory system not passing the thalamus.

Conclusion:

Our data suggest that impaired habituation in functional brain systems in migraine is fundamental only to specific modalities including the trigemino-nociceptive, but, at least, excluding the olfactory system. Our findings further suggest that there is no single neuronal modulator responsible for the altered rating pattern in migraineurs.

Pathophysiology of migraine

Migraine is a collection of perplexing neurological conditions in which the brain and its associated tissues have been implicated as major players during an attack. Once considered exclusively a disorder of blood vessels, compelling evidence has led to the realization that migraine represents a highly choreographed interaction between major inputs from both the peripheral and central nervous systems, with the trigeminovascular system and the cerebral cortex among the main players. Advances in in vivo and in vitro technologies have informed us about the significance to migraine of events such as cortical spreading depression and activation of the trigeminovascular system and its constituent neuropeptides, as well as about the importance of neuronal and glial ion channels and transporters that contribute to the putative cortical excitatory/inhibitory imbalance that renders migraineurs susceptible to an attack. This review focuses on emerging concepts that drive the science of migraine in both a mechanistic direction and a therapeutic direction.

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.

Brainstem 1H-MR spectroscopy in episodic and chronic migraine

The pathogenesis of evolution from episodic migraine (EM) to chronic migraine (CM) has not yet been clearly determined. Some studies revealed that dysfunction of the brainstem may play a role. We aimed to determine the brainstem ¹H-MR spectroscopic (MRS) findings in episodic and chronic migraine. We recruited patients with EM, CM and controls. Patients with CM were divided into subgroups with and without medication overuse (MO). The ¹H-MRS metabolite ratios at the periaqueductal gray (PAG) and bilateral dorsal pons were measured and compared with those in controls. A total of 19 patients with EM, 53 patients with CM (with MO n = 30, without MO n = 23) and 16 control subjects completed the study. Patients with EM had the highest N-acetylaspartate (NAA)/creatine (Cr) ratio at the dorsal pons (right, P = 0.014; left, P = 0.034) in comparison with those of CM and controls. The latter two groups did not differ. Among migraine patients, NAA/Cr ratios at dorsal pons were inversely correlated with headache frequency (right, r = −0.350, P = 0.004; left, r = −0.284, P = 0.019) and intensity (right, r = −0.286, P = 0.019; left, r = −0.244, P = 0.045), but not disease duration. In contrast, the metabolite ratios did not differ at the PAG among the study groups. Of note, MO was not associated with brainstem MRS ratios in patients with CM. The increased NAA/Cr levels may suggest neuronal hypertrophy at the dorsal pons in EM. A progressive dysfunction of this region may occur from EM to CM since the levels declined with increasing headache frequency and intensity.

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.

Beyond Beauty: Onobotulinumtoxin A (BOTOX®) and the Management of Migraine Headaches

Based on the conducted anatomic studies at our institutions as well as clinical experience with migraine surgery, we have refined our onobotulinumtoxin A (BOTOX®) injection techniques. Pain management physicians are in unique position to be able to not only treat migraine patient, but also to be able to collaborate with neurologists and peripheral nerve surgeons in identifying the migraine trigger sites prior to surgical deactivation. The constellation of migraine symptoms that aid in identifying the migraine trigger sites, the potential pathophysiology of each trigger site, the effective methods of botulinumtoxin and nerve block injection for diagnostic and treatment purposes, as well as the pitfalls and potential complications, will be addressed and discussed in this paper.

Migraine: a disorder of brain excitatory-inhibitory balance?

Migraine is a common disabling brain disorder whose key manifestations are recurrent attacks of unilateral headache and interictal hypersensitivity to sensory stimuli. Migraine arises from a primary brain dysfunction that leads to episodic activation and sensitization of the trigeminovascular pain pathway and as a consequence to headache. Major open issues concern the molecular and cellular mechanisms of the primary brain dysfunction(s) and of migraine pain. We review here our current understanding of these mechanisms, focusing on recent advances regarding migraine genetics, headache mechanisms, and the primary brain dysfunction(s) underlying migraine onset and susceptibility to cortical spreading depression, the neurophysiological correlate of migraine aura. We also discuss insights obtained from the functional analysis of familial hemiplegic migraine mouse models.