Electrophysiological studies in migraine: a comprehensive review of their interest and limitations

Prodrug approaches to reduce hyperexcitation in the CNS

Hyperexcitation in the central nervous system is the root cause of a number of disorders of the brain ranging from acute injury to chronic and progressive diseases. The major limitation to treatment of these ailments is the miniscule, yet formidable blood-brain barrier. To deliver therapeutic agents to the site of desired action, a number of biomedical engineering strategies have been developed including prodrug formulations that allow for either passive diffusion or active transport across this barrier. In the case of prodrugs, once in the brain compartment, the active therapeutic agent is released. In this review, we discuss in some detail a number of factors related to treatment of central nervous system hyperexcitation including molecular targets, disorders, prodrug strategies, and focused case studies of a number of therapeutics that are at a variety of stages of clinical development.

Absence of haemodynamic refractory effects in patients with migraine without aura – an interictal fMRI study

Background: In healthy controls, haemodynamic refractory effects are observed with blood-oxygenation-level dependent (BOLD) functional MRI (fMRI): the haemodynamic response function (HRF) to the second stimulus in a pair of stimuli with short interstimulus interval (ISI) shows a decreased amplitude and an increased time-to-peak. We hypothesize that there may be interictal haemodynamic abnormalities in migraineurs.

Methods: An event-related fMRI design with paired face stimuli and varying ISIs was used to measure interictal HRFs in the face recognition area of patients with migraine without aura (MwoA) and controls. Net responses to the second stimulus in a pair were calculated and averaged per participant. Several characterizing parameters of the net responses were quantified and examined within each group.

Results: Refractory effects were not observed in our patient group. There are no changes in the net responses compared with the reference situation in patients, irrespective of the ISI, whereas in controls all HRF parameters are decreased or delayed for an ISI of 1 second.

Conclusion: This is the first fMRI study investigating the haemodynamic refractory effects in MwoA patients. Unlike in controls, these effects are not observed in migraineurs. Although currently unclear, it is tempting to speculate that this observation reflects the neurovascular correlate of lack of habituation measured with evoked potentials in migraineurs.

Migraine pathophysiology

SUMMARY Our understanding of migraine pathophysiology is a work in progress, largely because of the absence of any identifiable cephalic pathology. There are currently two main theories on the genesis of migraine pain. One hypothesizes that the origin is in the periphery, requiring the activation of primary afferent nociceptive neurons that innervate cephalic tissue. The other theorizes that the origin of migraine pain is in the CNS, as a result of abnormal processing of sensory signals, rather than the activation of nociceptors. After briefly reviewing the clinical presentation and diagnosis of migraine, this article focuses on explaining the traditional and current theories of migraine pathogenesis.

Visual and auditory perceptual rivalry in migraine

INTRODUCTION

Recent evidence demonstrates that perceptual rivalry rate can be modulated by perturbation of the serotonergic system. Specifically, pharmacologically lowering the availability of serotonin results in slower rivalry rates. As it has been suggested that brain serotonin is low during the interictal phase of migraine, we hypothesized that perceptual rivalry rates would be reduced in individuals with migraine.

METHODS

Visual and auditory perceptual rivalry measures were obtained for a group of 30 participants with migraine (15 migraine with aura, 15 migraine without aura) and 20 non-headache control individuals.

RESULTS

Our experiments reveal fewer perceptual rivalry switches within both visual and auditory domains for our migraine without aura group, while the with-aura group performed similarly to non-headache controls. Dividing the data by headache frequency rather than headache subtype classification revealed fewer perceptual switches in those with more frequent headaches.

CONCLUSIONS

Our data provides further support for interictal differences in brain sensory reactivity in migraine, with the observed effects being in the same direction as those caused by pharmacologically reducing brain availability of serotonin in normal observers.

[Transcranial magnetic stimulation (TMS) in basic and clinical neuroscience research]

INTRODUCTION

Non-invasive brain stimulation methods such as transcranial magnetic stimulation (TMS) are starting to be widely used to make causality-based inferences about brain-behavior interactions. Moreover, TMS-based clinical applications are under development to treat specific neurological or psychiatric conditions, such as depression, dystonia, pain, tinnitus and the sequels of stroke, among others.

BACKGROUND

TMS works by inducing non-invasively electric currents in localized cortical regions thus modulating their activity levels according to settings, such as frequency, number of pulses, train and regime duration and intertrain intervals. For instance, it is known for the motor cortex that low frequency or continuous patterns of TMS pulses tend to depress local activity whereas high frequency and discontinuous TMS patterns tend to enhance it. Additionally, local cortical effects of TMS can result in dramatic patterns in distant brain regions. These distant effects are mediated via anatomical connectivity in a magnitude that depends on the efficiency and sign of such connections.

PERSPECTIVES

An efficient use of TMS in both fields requires however, a deep understanding of its operational principles, its risks, its potential and limitations. In this article, we will briefly present the principles through which non-invasive brain stimulation methods, and in particular TMS, operate.

CONCLUSION

Readers will be provided with fundamental information needed to critically discuss TMS studies and design hypothesis-driven TMS applications for cognitive and clinical neuroscience research.

Trigeminal nociceptive transmission in migraineurs predicts migraine attacks

Several lines of evidence suggest a major role of the trigeminovascular system in the pathogenesis of migraine. Using functional magnetic resonance imaging (fMRI), we compared brain responses during trigeminal pain processing in migraine patients with those of healthy control subjects. The main finding is that the activity of the spinal trigeminal nuclei in response to nociceptive stimulation showed a cycling behavior over the migraine interval. Although interictal (i.e., outside of attack) migraine patients revealed lower activations in the spinal trigeminal nuclei compared with controls, preictal (i.e., shortly before attack) patients showed activity similar to controls, which demonstrates that the trigeminal activation level increases over the pain-free migraine interval. Remarkably, the distance to the next headache attack was predictable by the height of the signal intensities in the spinal nuclei. Migraine patients scanned during the acute spontaneous migraine attack showed significantly lower signal intensities in the trigeminal nuclei compared with controls, demonstrating activity levels similar to interictal patients. Additionally we found-for the first time using fMRI-that migraineurs showed a significant increase in activation of dorsal parts of the pons, previously coined "migraine generator." Unlike the dorsal pons activation usually linked to migraine attacks, the gradient-like activity following nociceptive stimulation in the spinal trigeminal neurons likely reflects a raise in susceptibility of the brain to generate the next attack, as these areas increase their activity long before headache starts. This oscillating behavior may be a key player in the generation of migraine headache, whereas attack-specific pons activations are most likely a secondary event.

Migraine and motion sickness independently contribute to visual discomfort

The objective of this study was to evaluate, in patients with migraine and healthy volunteers, with and without a history of motion sickness, the degree of discomfort elicited by drifting striped patterns. Eighteen healthy volunteers (HV) and 30 migraine patients participated in the study. Discomfort was greater in migraine patients than in HV, and in individuals with a history of motion sickness than in those without, but the effect of history of migraine was independent of history of motion sickness. Generalized Estimating Equations models for binary correlated data revealed that these differences did not depend on levels of duty cycle, spatial and temporal frequencies. Visual discomfort in migraine patients was associated with worse performance. There was a significant correlation between median degree of discomfort across conditions and number of migraine attacks in the past month. Discomfort to drifting striped patterns may be related to central sensitization in migraine patients.

Photic EEG-driving responses related to ictal phases and trigger sensitivity in migraine: a longitudinal, controlled study

INTRODUCTION

Photic driving is believed to be increased in migraineurs and has been interpreted as a sign of cortical hyperexcitability. However, most previous studies have included patients in various phases of the migraine cycle. The results are, therefore, difficult to interpret as neurophysiological abnormalities tend to accumulate close to the attack in migraineurs.

SUBJECTS AND METHODS

We recorded steady state visual evoked EEG-responses (SSVEPs) for 6, 12, 18 and 24 Hz flash stimuli from 33 migraineurs without aura, eight migraineurs with aura and 32 healthy controls. Interictal recordings were compared pair-wise with recordings before, during and after attack, as well as with EEGs from healthy controls. Driving power was also correlated with sensory hypersensitivity and severity of migraine.

RESULTS

Between attacks, driving responses to 18 Hz and 24 Hz were attenuated in migraineurs without aura. Driving power of 12 Hz increased before the attack. Attack trigger sensitivity, photophobia, pain intensity and a family history of migraine were related to decreased and/or symmetric photic driving.

CONCLUSIONS

Earlier results may have overestimated the driving response in migraine due to inclusion of recordings during the preictal interval and/or habituation among controls. Abnormal photic driving may be related to the pathophysiology of clinical sensory hypersensitivity.

Neurophysiological tests and neuroimaging procedures in non-acute headache (2nd edition)

BACKGROUND AND PURPOSE

A large number of instrumental investigations are used in patients with non-acute headache in both research and clinical fields. Although the literature has shown that most of these tools contributed greatly to increasing understanding of the pathogenesis of primary headache, they are of little or no value in the clinical setting.

METHODS

This paper provides an update of the 2004 EFNS guidelines and recommendations for the use of neurophysiological tools and neuroimaging procedures in non-acute headache (first edition). Even though the period since the publication of the first edition has seen an increase in the number of published papers dealing with this topic, the updated guidelines contain only minimal changes in the levels of evidence and grades of recommendation.

RESULTS

(i) Interictal EEG is not routinely indicated in the diagnostic evaluation of patients with headache. Interictal EEG is, however, indicated if the clinical history suggests a possible diagnosis of epilepsy (differential diagnosis). Ictal EEG could be useful in certain patients suffering from hemiplegic or basilar migraine. (ii) Recording evoked potentials is not recommended for the diagnosis of headache disorders. (iii) There is no evidence warranting recommendation of reflex responses or autonomic tests for the routine clinical examination of patients with headache. (iv) Manual palpation of pericranial muscles, with standardized palpation pressure, can be recommended for subdividing patient groups but not for diagnosis. Pain threshold measurements and EMG are not recommended as clinical diagnostic tests. (v) In adult and pediatric patients with migraine, with no recent change in attack pattern, no history of seizures, and no other focal neurological symptoms or signs, the routine use of neuroimaging is not warranted. In patients with trigeminal autonomic cephalalgia, neuroimaging should be carefully considered and may necessitate additional scanning of intracranial/cervical vasculature and/or the sellar/orbital/(para)nasal region. In patients with atypical headache patterns, a history of seizures and/or focal neurological symptoms or signs, MRI may be indicated. (vi) If attacks can be fully accounted for by the standard headache classification (IHS), a PET or SPECT scan will normally be of no further diagnostic value. Nuclear medical examinations of the cerebral circulation and metabolism can be carried out in subgroups of patients with headache for the diagnosis and evaluation of complications, when patients experience unusually severe attacks or when the quality or severity of attacks has changed. (vii) Transcranial Doppler examination is not helpful in headache diagnosis.

CONCLUSION

Although many of the examinations described in the present guidelines are of little or no value in the clinical setting, most of the tools, including thermal pain thresholds and transcranial magnetic stimulation, have considerable potential for differential diagnostic evaluation as well as for the further exploration of headache pathophysiology and the effects of pharmacological treatment.

Visual metacontrast masking in migraine

Background: In visual metacontrast masking, the visibility of a brief target stimulus can be reduced substantially if it is preceded (forward masking) or followed (backward masking) by a non-overlapping mask. These effects have been attributed to inhibitory processes within the visual system. Two previous studies have used metacontrast masking to assess inhibitory function in migraine and control groups, however, each used different types of masking and obtained different results.

Subjects and Methods: Forward, backward and combined forward and backward masking were compared in migraine (15 with visual aura, 15 without) and control ( n = 15) groups. Baseline trials were also included (target only).

Results: For all types of masking, both migraine groups were more accurate than the control group. When performance for the masking trials was expressed relative to baseline, however, there were no significant group differences. Performance in certain conditions nevertheless correlated significantly with migraine frequency and with the recency of the last attack.

Conclusions: The inhibitory processes involved in the masking tasks employed in this study do not appear to be impaired in migraine. Their better overall performance may reflect a sensitivity difference, perhaps as a consequence of a heightened neuronal response, which varies with the migraine cycle.

Neurofeedback and biofeedback with 37 migraineurs: a clinical outcome study

Background

Traditional peripheral biofeedback has grade A evidence for effectively treating migraines. Two newer forms of neurobiofeedback, EEG biofeedback and hemoencephalography biofeedback were combined with thermal handwarming biofeedback to treat 37 migraineurs in a clinical outpatient setting.

Methods

37 migraine patients underwent an average of 40 neurofeedback sessions combined with thermal biofeedback in an outpatient biofeedback clinic. All patients were on at least one type of medication for migraine; preventive, abortive or rescue. Patients kept daily headache diaries a minimum of two weeks prior to treatment and throughout treatment showing symptom frequency, severity, duration and medications used. Treatments were conducted an average of three times weekly over an average span of 6 months. Headache diaries were examined after treatment and a formal interview was conducted. After an average of 14.5 months following treatment, a formal interview was conducted in order to ascertain duration of treatment effects.

Results

Of the 37 migraine patients treated, 26 patients or 70% experienced at least a 50% reduction in the frequency of their headaches which was sustained on average 14.5 months after treatments were discontinued.

Conclusions

All combined neuro and biofeedback interventions were effective in reducing the frequency of migraines with clients using medication resulting in a more favorable outcome (70% experiencing at least a 50% reduction in headaches) than just medications alone (50% experience a 50% reduction) and that the effect size of our study involving three different types of biofeedback for migraine (1.09) was more robust than effect size of combined studies on thermal biofeedback alone for migraine (.5). These non-invasive interventions may show promise for treating treatment-refractory migraine and for preventing the progression from episodic to chronic migraine.

The clinical neurophysiology of tension-type headache

Despite being widely investigated, the pathogenesis of tension-type headache (TTH) continues to be debated. Among the different approaches used to explore the mechanisms underlying TTH, clinical neurophysiology plays an important role. Studies to date have focused mainly on two areas: (1) evaluation of peripheral factors (i.e., by electromyography (EMG)); and (2) exploration of the role of the pain control system. In the second of these areas, a large number of studies have explored trigeminal pathways, in particular using reflexes (e.g., the trigeminofacial reflex, trigeminotrigeminal reflexes). More recently, the descending inhibitory system, known to modulate both the trigeminal and the spinal system, has also been investigated. In addition, several studies have sought to establish whether there are neurophysiological parameters that could be markers of this condition, but the results of these were inconclusive, since some abnormalities could frequently be observed in migraine too. This chapter critically reviews the clinical neurophysiology of TTH. It concludes that the majority of neurophysiological studies on TTH present serious methodological flaws that will have to be overcome to allow further understanding of the mechanisms of TTH.

Pain perception and laser evoked potentials during menstrual cycle in migraine

The association between estrogens “withdrawal” and attacks of migraine without aura is well-known. The aim of the study was to examine the features of laser evoked potentials (LEPs), including habituation, in women suffering from migraine without aura versus healthy controls, during the pre-menstrual and late luteal phases. Nine migraine without aura and 10 non-migraine healthy women, were evaluated during the pre-menstrual phase and late luteal phase. The LEPs were recorded during the inter-critical phase. The right supraorbital zone and the dorsum of the right hand were stimulated. Three consecutive series of 20 laser stimuli were obtained for each stimulation site. Laser pain perception was rated by a 0–100 VAS after each stimulation series. Migraine patients exhibited increased LEPs amplitude and reduced habituation compared to normal subjects. Laser-pain perception was increased during the pre-menstrual phase in both patients and controls. Migraine patients and controls showed increased P2 and N2–P2 amplitude in the pre-menstrual phase, on both stimulation sites. During the pre-menstrual phase the N2–P2 habituation appeared to be reduced in both migraine and healthy women. The estrogen withdrawal occurring during the menstrual cycle may favor reduced habituation of nociceptive cortex, which may facilitate pain symptoms and migraine in predisposed women.

State-dependent variability of neuronal responses to transcranial magnetic stimulation of the visual cortex

Electrical brain stimulation is a promising tool for both experimental and clinical applications. However, the effects of stimulation on neuronal activity are highly variable and poorly understood. To investigate the basis of this variability, we performed extracellular recordings in the visual cortex following application of transcranial magnetic stimulation (TMS). Our measurements of spiking and local field potential activity exhibit two types of response patterns which are characterized by the presence or absence of spontaneous discharge following stimulation. This variability can be partially explained by state-dependent effects, in which higher pre-TMS activity predicts larger post-TMS responses. These results reveal the possibility that variability in the neural response to TMS can be exploited to optimize the effects of stimulation. It is conceivable that this feature could be utilized in real time during the treatment of clinical disorders.

Migraine in the triptan era: lessons from epidemiology, pathophysiology, and clinical science

The triptan era has been a time of remarkable progress for migraine diagnosis and treatment. In this paper, we review some of the advances achieved in migraine science during this era focusing on 3 themes: lessons from clinical practice, lessons from epidemiology and lessons from pathophysiology. Science has shown that migraine is a disorder of the brain, and that the key events happen in the the trigeminal neuronal pathways, not on blood vessels. Clinical science has led to the observation that migraine sometimes progresses or remits. This in turn led to longitudinal epidemiologic studies focusing on factors that determine migraine prognosis. In addition, these studies raised questions about the mechanisms of migraine progression, including the role of allodynia, obesity, inflammation, and medications as determinants of progression. This in turn opens a new set of scientific questions about the neurobiologic determinants of migraine, as well as of its clinical course, and exciting opportunities to develop new therapies for this highly disabling brain disorder.

Effects of Rizatriptan on the Contingent Negative Variation in Healthy Women

The effect of the antimigraine drug rizatriptan on the amplitude and habituation of the contingent negative variation (CNV) in healthy women was examined in a randomized, double-blind, placebo-controlled trial. The test persons were assigned either to a drug ( n = 20) or a placebo group ( n = 20). The CNV was recorded three times: before, directly after, and 24 h after drug or placebo intake. The CNV paradigm was presented in a standard, a cued and a choice version. Rizatriptan led to an increase of CNV amplitude that depended on the level of difficulty of the task. Whereas there was no drug effect in the standard version, an amplitude increase was obtained mainly in the choice task. The results are in line with the ceiling theory of migraine, which assumes a rise of CNV amplitude if the serotonin level is lowered.

Quantitative EEG Power and Asymmetry Increase 36 h Before a Migraine Attack

The aim was to estimate ictal, pre- and postictal brain function changes in migraine in a blinded paired quantitative EEG (QEEG) study. EEG recordings ( n = 119) from 40 migraineurs were retrospectively classified as ictal, interictal, preictal or postictal. δ, θ, α and β power, and hemispheric asymmetry in frontocentral, temporal and occipitoparietal regions were calculated from artefact-free EEG. Power and power asymmetry were calculated for two time-windows, 36 and 72 h before/after the attack, and compared with the interictal values. Frontocentral δ power increased ( P = 0.03), whereas frontocentral θ and α power tended to increase ( P < 0.09) within 36 h before the next attack compared with the interictal period. Occipitoparietal (α and θ) and temporal (α) power were more asymmetric before the attack compared with the interictal baseline ( P < 0.04). Ictal posterior a power increased slightly ( P = 0.01). Postictal power and power asymmetry were not significantly different from interictal baseline. EEG activity seems to change shortly before the attack. This suggests that migraineurs are most susceptible to attack when anterior QEEG δ power and posterior α and θ asymmetry values are high. Changed activity patterns in cholinergic brainstem or basal forebrain nuclei and thalamo-cortical connections before the migraine attack are hypothesized.

Serotonin and migraine: a reconsideration of the central theory

The 5-hydroxytryptamine (5-HT) has been implicated in migraine pathophysiology for the past 50 years. A low central 5-HT disposition associated with an increase in 5-HT release during attack is the most convincing change of 5-HT metabolism implicated in migraine. Peripheral studies on plasma/platelet have not generally shown low 5-HT levels. Studies on 5-HT reactivity showed hypersensitivity, also expressed as reduced tachyphylaxis (habituation), which successively was evidenced as the most characteristic marker of an altered sensory neurotransmission. Even the gender and seasonal variations of 5-HT parameters seem to agree with a low 5-HT turnover with receptoral hypersensitivity. The interpretation of the effects of some serotonergic drugs and recent neuroimaging studies give major evidence for this cascade of events. Although the exact mechanism that links abnormal 5-HT neurotransmission to the manifestation of head pain has yet to be fully understood, a deficit on 5-HT descending pain inhibitory system is still probably today the most implicated in migraine pathophysiology. This short review focuses and discusses the alteration of peripheral and central 5-HT parameters in migraine patients.

[Cortical dysbalance in the brain in migraineurs--hyperexcitability as the result of sensitisation?]

A cortical dysbalance has a pivotal role in the pathophysiology of migraine. Numerous electrophysiological and transcranial magnetic stimulation (TMS) studies have investigated the interictal excitability level in migraineurs and have shown a consistent lack of habituation during repetitive stimulation. There is some controversy in the current literature over whether this deficit is based on a lowered or an elevated preactivation level. However, the current discussion may be misguided. It seems that multiple external and intrinsic factors influence the level of cortical excitability and the frequency and intensity of attacks: Habituation is specific neither to migraine nor even to pain; the same phenomenon is found in tinnitus patients, for example. Cortical hyperexcitability is presumably the result of chronicity and the concomitant central sensitisation process.

Longitudinal assessment of response preparation and evaluation in migraine gives evidence for deviant maturation

Evidence for deviant maturation of sensory processing in migraine has come recently from cross-sectional studies during childhood. Age-dependent development of response preparation and evaluation is characterized using a longitudinal design in school-aged migraine patients and controls in order to challenge the hypothesis of migraine as a maturation disorder. Forty-six children with migraine and 57 healthy controls aged 6-18 years were investigated and followed up 4 years later using a simple acoustic contingent negative variation (CNV) paradigm. Maturation in controls was characterized by increasing negativity of late and total CNV and stability of initial CNV (iCNV) and the motor postimperative negative variation (mPINV). Migraine patients showed a lack of development for late and total CNV and decreasing iCNV and mPINV negativity. This first longitudinal study confirms cross-sectional results of deviant CNV maturation in migraine. Altered maturation was not correlated with clinical improvement and may represent a vulnerability marker for migraine.

Effects of Topiramate on Migraine Frequency and Cortical Excitability in Patients with Frequent Migraine

We studied the excitability of the visual and motor cortex in 36 patients with frequent migraine without aura (30 women, mean age 38.6 ± 10.0 years) before and after treatment with topiramate (100 mg/day) using transcranial magnetic stimulation. Treatment with topiramate resulted in reduction of both headache frequency (12.0 ± 1.3 to 5.8 ± 3.2 migraine days per month; P = 0.004) and cortical excitability: motor cortex thresholds increased on the right side from 43.8 ± 7.5% to 47.7 ± 9.2% ( P = 0.049) and on the left side from 43.4 ± 7.0% to 47.2 ± 9.6% ( P = 0.047), and phosphene thresholds increased from 58.9 ± 11.1% to 71.2 ± 11.2% ( P = 0.0001). Reduction of headache frequency correlated inversely with an increase of visual thresholds and did not correlate with motor thresholds. The effect of topiramate in migraine prevention is complex and can not be explained simply by inhibition of cortical excitability.

Is the cerebral cortex hyperexcitable or hyperresponsive in migraine?

Although migraineurs appear in general to be hypersensitive to external stimuli, they maybe also have increased daytime sleepiness and complain of fatigue. Neurophysiological studies between attacks have shown that for a number of different sensory modalities the migrainous brain is characterised by a lack of habituation of evoked responses. Whether this is due to increased cortical hyperexcitability, possibly due to decreased inhibition, or to an abnormal responsivity of the cortex due a decreased preactivation level remains disputed. Studies using transcranial magnetic stimulation in particular have yielded contradictory results. We will review here the available data on cortical excitability obtained with different methodological approaches in patients over the migraine cycle. We will show that these data congruently indicate that the sensory cortices of migraineurs react excessively to repetitive, but not to single, stimuli and that the controversy above hyper- versus hypo-excitability is merely a semantic misunderstanding. Describing the migrainous brain as 'hyperresponsive' would fit most of the available data. Deciphering the precise cellular and molecular underpinnings of this hyperresponsivity remains a challenge for future research. We propose, as a working hypothesis, that a thalamo-cortical dysrhythmia might be the culprit.

Evaluation and proposal for optimalization of neurophysiological tests in migraine: part 1--electrophysiological tests

Neurophysiological testing has become a valuable tool for investigating brain excitability and nociceptive systems in headache disorders. Previous reviews have suggested that most neurophysiological tests have limited value for headache diagnosis, but a vast potential for exploring the pathophysiology of headaches, the central effects of certain pharmacological treatments and phenotype-genotype correlations. Many protocols, however, lack standardization. This meta-analytical review of neurophysiological methods in migraine was initiated by a task force within the EUROHEAD project (EU Strep LSHM-CT-2004-5044837-Workpackage 9). Most of the neurophysiological approaches that have been used in headache patients are reviewed, i.e. evoked potentials, nociception-specific blink reflex, single-fibre electromyography, neuroimaging methods (functional MRI, PET, and voxel-based morphometry) and the nitroglycerin attack-provoking test. For each of them, we summarize the results, analyse the methodological limitations and propose recommendations for improved methodology and standardization of research protocols. The first part is devoted to electrophysiological methods, the second to neuroimaging techniques and the NTG test.

Migraine aura

Recurrent episodes of transient focal neurologic symptoms, known as aura, occur in association with migraine headache in about 11.9 million people in the United States. At present, the International Headache Society has recognized 3 "typical" auras: visual, sensory, and language. Increasing evidence from investigations in human subjects suggests that typical auras may be the clinical manifestation of a cortical spreading depression (CSD)-like phenomenon. Other studies have shown altered reactivity and processing within the cortices of migraineurs who experience an aura, which might render them more vulnerable to CSD-like events. Recent investigations also support the hypothesis that events intrinsic to the cerebral cortex are capable of activating trigeminal nociceptive neurons and of affecting the caliber of vascular structures innervated by them. A better understanding of the mechanisms underlying the aura may potentially lead to more effective therapies, which will aim at preventing migraine headaches before they start.

The triggers or precipitants of the acute migraine attack

The aim of this study was to evaluate and define the triggers of the acute migraine attack. Patients rated triggers on a 0-3 scale for the average headache. Demographics, prodrome, aura, headache characteristics, postdrome, medication responsiveness, acute and chronic disability, sleep characteristics and social and personal characteristics were also recorded. One thousand two hundred and seven International Classification of Headache Disorders-2 (1.1-1.2, and 1.5.1) patients were evaluated, of whom 75.9% reported triggers (40.4% infrequently, 26.7% frequently and 8.8% very frequently). The trigger frequencies were stress (79.7%), hormones in women (65.1%), not eating (57.3%), weather (53.2%), sleep disturbance (49.8%), perfume or odour (43.7%), neck pain (38.4%), light(s) (38.1%), alcohol (37.8%), smoke (35.7%), sleeping late (32.0%), heat (30.3%), food (26.9%), exercise (22.1%) and sexual activity (5.2%). Triggers were more likely to be associated with a more florid acute migraine attack. Differences were seen between women and men, aura and no aura, episodic and chronic migraine, and between migraine and probable migraine.

Influence of MTHFR Genotype on Contingent Negative Variation And MRI Abnormalities in Migraine

BACKGROUND

The MTHFR C677T genotype has been associated with increased risk of migraine, particularly of migraine with aura (MA) in selected clinical samples and with elevated homocysteine. The hyper-homocysteinemia may favor the vascular and neuronal mechanism underlying migraine, and the risk of stroke.

OBJECTIVE

The first aim of the present study was to examine the Contingent Negative Variation (CNV) amplitude and habituation pattern in a migraine sample versus non-migraine subjects, at the light of the MTHFR genotype, according to an unrelated and clinical based case-control panel. The second aim was to compare the frequency of Magnetic Resonance Imaging (MRI) subclinical brain lesions across the different C677 genotypes in the same migraine sample, selected for the young age and the absence of any cardiovascular risk factor.

METHODS

One hundred and five 18-45 year old out-patients, 90 affected by migraine without aura (MO) and 15 by MA, and 97 non-migraine healthy subjects, age and sex matched, were selected for the genetic analysis. All subjects had a common ethnic origin from Puglia. Sixty-four migraine subjects and 33 control subjects were submitted to the recording of the CNV. All migraine subjects underwent the MRI evaluation.

RESULTS

The frequency of homozygosis was 14.33% in normal subjects, versus 25.7% in MA + MO group (chi2-test: 10.80 P= .001). The frequency of homozygosis in MO patients, was 25.5% (MA versus N: chi2-test: 9 P= .003), in MA group it was 26.6%. Considering the MTHFR genotype in migraine patients and controls, the C677TT subjects exhibited a reduced habituation index of the early CNV (iCNV), in respect with both C677TC and C677CC; in the migraine group, there was a significant decrease of CNV habituation in patients with homozygosis and a positive correlation between the habituation index values and the homocysteine levels. Nineteen migraine patients exhibited subclinical brain lesions (18.05%): patients with C677T homozygosis did not exhibit a higher risk for MRI abnormalities.

CONCLUSIONS

This unrelated and clinical based case-control study showed that genetically induced hyper-homocysteinemia may favor the neuronal factors predisposing to migraine, while it does not influence the presence of subclinical vascular brain lesions probably linked with increased risk of stroke.

New insights into migraine pathophysiology

PURPOSE OF REVIEW

This article will review new and exciting developments in migraine research, with particular emphasis on mutations associated with familial hemiplegic migraine and the role of cortical spreading depression in its pathophysiology and treatment.

RECENT FINDINGS

The recent discovery of multiple point mutations in familial hemiplegic migraine has led to the suggestion that migraine and its variants may be due to a paroxysmal disturbance in ion-translocating mechanisms. Mutations associated with familial hemiplegic migraine render the brain more susceptible to prolonged cortical spreading depression caused by either excessive synaptic glutamate release or decreased removal of glutamate and potassium from the synaptic cleft, or persistent sodium influx. Suppression of cortical spreading depression has become an interesting target for preventive migraine treatment. Prolonged treatment with beta-blockers, valproate, topiramate, methysergide or amitriptyline reduced the number of potassium-evoked cortical spreading depressions and elevated the electrical stimulation threshold for the induction of cortical spreading depression in rats. Recent imaging studies in patients suffering from migraine without aura also point to the presence of silent cortical spreading depression as an underlying mechanism. Repeated waves of cortical spreading depression may have deleterious effects on brain function, and perhaps cause silent ischaemic lesions in vulnerable brain regions such as the cerebellum in susceptible individuals.

SUMMARY

This review emphasizes several neurobiological aspects of migraine that reveal paroxysmal disturbances in neuronal and vascular function, that in turn reflect disturbances in the maintenance of ionic gradients.

Tryptophan depletion increases nausea, headache and photophobia in migraine sufferers

Sensitivity to light was investigated 5 and 8 h after consumption of an amino acid drink which contained L-tryptophan (balanced amino acid condition: 19 controls and 22 migraine sufferers) or which produced a short-term reduction in brain serotonin synthesis by omitting L-tryptophan (tryptophan depletion condition: 16 controls and 16 migraine sufferers). Migraine sufferers reported more intense nausea, headache, glare- and light-induced pain than controls. In addition, glare- and light-induced pain were greater in the tryptophan depletion condition than in the balanced amino acid condition, in both migraine sufferers and controls. Eight hours after the amino acid drink, after participants had completed tests of pain sensitivity and motion sickness provocation, tryptophan depletion augmented headache in migraine sufferers and aggravated nausea in migraine sufferers and controls. These findings suggest that a reduction in brain synthesis of serotonin intensifies photophobia and other migrainous symptoms and thus might contribute to the pathogenesis of migraine.

Migraine: a review and future directions for treatment

Migraine is a chronic, neurological disorder generally manifesting itself in attacks with severe headache, nausea and an increased reactivity to sensory stimuli. A low migraine threshold is set by genetic factors, although the phenotype also modulates the manifestations. The 1-year prevalence is approximately 13% and is higher among women. Patients usually experience neuropsychological dysfunction, and sometimes also reversible focal neurological symptoms. The trajectories of the characteristic symptoms of acute migraine usually follow a similar time course, indicating a reciprocal underlying mechanism. A central nervous system hyperexcitability has been demonstrated in neurophysiological studies. The dibilitating effects of migraine are not confined to the attacks per se. Many individuals do not recover completely between the attacks and most report a negative impact on the most important life domains, and an interest in testing other treatments. Young persons have a higher frequency of attacks. Acute treatment should routinely be initiated with an analgesic plus a prokinetic anti-emetic. Triptans must not be provided early during the attack to ensure their efficacy. The natural course of attacks is commonly only temporarily altered by acute treatment. Non-pharmacological treatment and drugs may be equally viable in prophylaxis for migraine. In more complicated cases, conjoint therapy should be considered. New strategies to improve adherence with existing therapeutic regimens might yield greater benefits than will new pharmacological agents.

Physiological Parameters as Biomarkers of Migraine

We review physical signs and measurements from neurophysiological research, which may be considered biomarkers of migraine. Most studies show that information processing is abnormal in migraineurs. Studies of trigeminal nociception are in line with a central sensitization during the attack. The best documented abnormality is an interictal lack of habituation in migraineurs, with a normalization during the headache state, which has been shown using evoked and event-related potentials. Together with a diminished energy reserve found in MR-spectroscopy studies, these results suggest a possible role of increased energy consumption in attack generation. Importantly, to date, no neurophysiological marker has a high enough sensitivity and specificity to point out the single migraine patient. Therefore, these biomarkers are to be understood as tools for research and are not to be used for diagnostic purposes.

Psychophysiological response patterns of migraine patients in two habituation tests

OBJECTIVE

To investigate the habituation response pattern of patients with migraine to a simple standard stressor and to a more complex performance-dependent (achievement) stressor in three peripheral systems (electrodermal, vasomotor, and cardiovascular). We hypothesized that the migraine patients would show abnormal habituation in these peripheral systems, especially in response to achievement stimuli.

BACKGROUND

Abnormal central habituation to repetitive stimuli has been reported frequently in patients with migraine. But little is known about habituation of the peripheral autonomic nervous system to stressors in these patients.

METHODS

A total of 30 female migraineurs and 30 physically and mentally healthy women matched for age and social status participated in a simple habituation test (auditory stimuli) and an achievement habituation test (mental arithmetic).

RESULTS

Habituation was impaired in the electrodermal (skin conductance response), vasomotor (pulse volume amplitude), and cardiovascular (heart rate response) systems during the mental arithmetic test (achievement stimuli) in the migraineurs as compared to the healthy controls. With the simple stressor (auditory stimuli), however, habituation was impaired in the vasomotor system only. Consistent with these findings were the participants' verbal reports, which indicated significantly more subjective tension in the migraine group than in the control group during the calculation test.

CONCLUSION

Our results suggest that the mental arithmetic (achievement) habituation paradigm is an important tool for demonstrating reduced habituation in several specific components of the autonomic nervous system. Further research is needed to target the covariance of central and autonomic nervous system habituation phenomena in migraine.

Processing of global form and motion in migraineurs

Previous studies have identified anomalies of cortical visual processing in migraineurs that appear to extend beyond V1. Migraineurs respond differently than controls to transcranial magnetic stimulation of V5, and can demonstrate impairments of global motion processing. This study was designed to assess the integrity of intermediate stages of both motion and form processing in people with migraine. We measured the ability to integrate local orientation information into a global form percept, and to integrate local motion information into a global motion percept. Control subjects performed significantly better than migraineurs on both tasks, suggesting a diffuse visual cortical processing anomaly in migraine.

Visually evoked phase synchronization changes of alpha rhythm in migraine: Correlations with clinical features

OBJECTIVE

This study aimed to compute phase synchronization of the alpha band from a multichannel electroencephalogram (EEG) recorded under repetitive flash stimulation from migraine patients without aura. This allowed examination of ongoing EEG activity during visual stimulation in the pain-free phase of migraine.

METHODS

Flash stimuli at frequencies of 3, 6, 9, 12, 15, 18, 21, 24, and 27 Hz were delivered to 15 migraine patients without aura and 15 controls, with the EEG recorded from 18 scalp electrodes, referred to the linked earlobes. The EEG signals were filtered in the alpha (7.5-13 Hz) band. For all stimulus frequencies that we evaluated, the phase synchronization index was based on the Hilbert transformation.

RESULTS

Phase synchronization separated the patients and controls for the 9, 24 and 27 Hz stimulus frequencies; hyper phase synchronization was observed in patients, whereas healthy subjects were characterized by a reduced phase synchronization. These differences were found in all regions of the scalp.

CONCLUSIONS

During migraine, the brain synchronizes to the idling rhythm of the visual areas under certain photic stimulations; in normal subjects however, brain regions involved in the processing of sensory information demonstrate desynchronized activity. Hypersynchronization of the alpha rhythm may suggest a state of cortical hypoexcitability during the interictal phase of migraine.

SIGNIFICANCE

The employment of non-linear EEG analysis may identify subtle functional changes in the migraine brain.