Alpha rhythm in classical migraine (migraine with aura): abnormalities in the headache-free interval

EEG Changes in Migraine-Can EEG Help to Monitor Attack Susceptibility?

Migraine is a highly prevalent brain condition with paroxysmal changes in brain excitability believed to contribute to the initiation of an attack. The attacks and their unpredictability have a major impact on the lives of patients. Clinical management is hampered by a lack of reliable predictors for upcoming attacks, which may help in understanding pathophysiological mechanisms to identify new treatment targets that may be positioned between the acute and preventive possibilities that are currently available. So far, a large range of studies using conventional hospital-based EEG recordings have provided contradictory results, with indications of both cortical hyper- as well as hypo-excitability. These heterogeneous findings may largely be because most studies were cross-sectional in design, providing only a snapshot in time of a patient's brain state without capturing day-to-day fluctuations. The scope of this narrative review is to (i) reflect on current knowledge on EEG changes in the context of migraine, the attack cycle, and underlying pathophysiology; (ii) consider the effects of migraine treatment on EEG features; (iii) outline challenges and opportunities in using EEG for monitoring attack susceptibility; and (iv) discuss future applications of EEG in home-based settings.

Alterations of the alpha rhythm in visual snow syndrome: a case-control study

BACKGROUND

Visual snow syndrome is a disorder characterized by the combination of typical perceptual disturbances. The clinical picture suggests an impairment of visual filtering mechanisms and might involve primary and secondary visual brain areas, as well as higher-order attentional networks. On the level of cortical oscillations, the alpha rhythm is a prominent EEG pattern that is involved in the prioritisation of visual information. It can be regarded as a correlate of inhibitory modulation within the visual network.

METHODS

Twenty-one patients with visual snow syndrome were compared to 21 controls matched for age, sex, and migraine. We analysed the resting-state alpha rhythm by identifying the individual alpha peak frequency using a Fast Fourier Transform and then calculating the power spectral density around the individual alpha peak (+/- 1 Hz). We anticipated a reduced power spectral density in the alpha band over the primary visual cortex in participants with visual snow syndrome.

RESULTS

There were no significant differences in the power spectral density in the alpha band over the occipital electrodes (O1 and O2), leading to the rejection of our primary hypothesis. However, the power spectral density in the alpha band was significantly reduced over temporal and parietal electrodes. There was also a trend towards increased individual alpha peak frequency in the subgroup of participants without comorbid migraine.

CONCLUSIONS

Our main finding was a decreased power spectral density in the alpha band over parietal and temporal brain regions corresponding to areas of the secondary visual cortex. These findings complement previous functional and structural imaging data at a electrophysiological level. They underscore the involvement of higher-order visual brain areas, and potentially reflect a disturbance in inhibitory top-down modulation. The alpha rhythm alterations might represent a novel target for specific neuromodulation.

TRIAL REGISTRATION

we preregistered the study before preprocessing and data analysis on the platform osf.org (DOI: https://doi.org/10.17605/OSF.IO/XPQHF , date of registration: November 19th 2022).

Electrophysiological findings in migraine may reflect abnormal synaptic plasticity mechanisms: A narrative review

BACKGROUND

The cyclical brain disorder of sensory processing accompanying migraine phases lacks an explanatory unified theory.

METHODS

We searched Pubmed for non-invasive neurophysiological studies on migraine and related conditions using transcranial magnetic stimulation, electroencephalography, visual and somatosensory evoked potentials. We summarized the literature, reviewed methods, and proposed a unified theory for the pathophysiology of electrophysiological abnormalities underlying migraine recurrence.

RESULTS

All electrophysiological modalities have determined specific changes in brain dynamics across the different phases of the migraine cycle. Transcranial magnetic stimulation studies show unbalanced recruitment of inhibitory and excitatory circuits, more consistently in aura, which ultimately results in a substantially distorted response to neuromodulation protocols. Electroencephalography investigations highlight a steady pattern of reduced alpha and increased slow rhythms, largely located in posterior brain regions, which tends to normalize closer to the attacks. Finally, non-painful evoked potentials suggest dysfunctions in habituation mechanisms of sensory cortices that revert during ictal phases.

CONCLUSION

Electrophysiology shows dynamic and recurrent functional alterations within the brainstem-thalamus-cortex loop varies continuously and recurrently in migraineurs. Given the central role of these structures in the selection, elaboration, and learning of sensory information, these functional alterations suggest chronic, probably genetically determined dysfunctions of the synaptic short- and long-term learning mechanisms.

Excitation-Inhibition Imbalance in Migraine: From Neurotransmitters to Brain Oscillations

Migraine is among the most common and debilitating neurological disorders typically affecting people of working age. It is characterised by a unilateral, pulsating headache often associated with severe pain. Despite the intensive research, there is still little understanding of the pathophysiology of migraine. At the electrophysiological level, altered oscillatory parameters have been reported within the alpha and gamma bands. At the molecular level, altered glutamate and GABA concentrations have been reported. However, there has been little cross-talk between these lines of research. Thus, the relationship between oscillatory activity and neurotransmitter concentrations remains to be empirically traced. Importantly, how these indices link back to altered sensory processing has to be clearly established as yet. Accordingly, pharmacologic treatments have been mostly symptom-based, and yet sometimes proving ineffective in resolving pain or related issues. This review provides an integrative theoretical framework of excitation-inhibition imbalance for the understanding of current evidence and to address outstanding questions concerning the pathophysiology of migraine. We propose the use of computational modelling for the rigorous formulation of testable hypotheses on mechanisms of homeostatic imbalance and for the development of mechanism-based pharmacological treatments and neurostimulation interventions.

Application of EEG in migraine

Migraine is a common disease of the nervous system that seriously affects the quality of life of patients and constitutes a growing global health crisis. However, many limitations and challenges exist in migraine research, including the unclear etiology and the lack of specific biomarkers for diagnosis and treatment. Electroencephalography (EEG) is a neurophysiological technique for measuring brain activity. With the updating of data processing and analysis methods in recent years, EEG offers the possibility to explore altered brain functional patterns and brain network characteristics of migraines in depth. In this paper, we provide an overview of the methodology that can be applied to EEG data processing and analysis and a narrative review of EEG-based migraine-related research. To better understand the neural changes of migraine or to provide a new idea for the clinical diagnosis and treatment of migraine in the future, we discussed the study of EEG and evoked potential in migraine, compared the relevant research methods, and put forwards suggestions for future migraine EEG studies.

Migraine Visual Aura and Cortical Spreading Depression-Linking Mathematical Models to Empirical Evidence

This review describes the subjective experience of visual aura in migraine, outlines theoretical models of this phenomenon, and explores how these may be linked to neurochemical, electrophysiological, and psychophysical differences in sensory processing that have been reported in migraine with aura. Reaction-diffusion models have been used to model the hallucinations thought to arise from cortical spreading depolarisation and depression in migraine aura. One aim of this review is to make the underlying principles of these models accessible to a general readership. Cortical spreading depolarisation and depression in these models depends on the balance of the diffusion rate between excitation and inhibition and the occurrence of a large spike in activity to initiate spontaneous pattern formation. We review experimental evidence, including recordings of brain activity made during the aura and attack phase, self-reported triggers of migraine, and psychophysical studies of visual processing in migraine with aura, and how these might relate to mechanisms of excitability that make some people susceptible to aura. Increased cortical excitability, increased neural noise, and fluctuations in oscillatory activity across the migraine cycle are all factors that are likely to contribute to the occurrence of migraine aura. There remain many outstanding questions relating to the current limitations of both models and experimental evidence. Nevertheless, reaction-diffusion models, by providing an integrative theoretical framework, support the generation of testable experimental hypotheses to guide future research.

[Neurophysiological methods in the assessment of different forms of migraine]

The review considers the efficacy of neurophysiological methods for the study of migraine. According to many authors, such neurophysiological methods as analysis of visual and somatosensory evoked potentials, trigeminal evoked potentials are informative for assessing the functional state of trigeminocervical and sensory systems. Analysis of bioelectric activity of the brain is used for differential diagnosis of migraine and epilepsy, evaluation of various forms and types of migraine. Studies with recording and analysis of laser evoked potentials, as well as the effects of transcranial magnetic stimulation, both diagnostic and non-pharmacological rehabilitation effects on pain syndrome, which increases the efficiency and quality of life in migraine, are considered.

Current understanding of cortical structure and function in migraine

Objective

To review and discuss the literature on the role of cortical structure and function in migraine.

Discussion

Structural and functional findings suggest that changes in cortical morphology and function contribute to migraine susceptibility by modulating dynamic interactions across cortical and subcortical networks. The involvement of the cortex in migraine is well established for the aura phase with the underlying phenomenon of cortical spreading depolarization, while increasing evidence suggests an important role for the cortex in perception of head pain and associated sensations. As part of trigeminovascular pain and sensory processing networks, cortical dysfunction is likely to also affect initiation of attacks.

Conclusion

Morphological and functional changes identified across cortical regions are likely to contribute to initiation, cyclic recurrence and chronification of migraine. Future studies are needed to address underlying mechanisms, including interactions between cortical and subcortical regions and effects of internal (e.g. genetics, gender) and external (e.g. sensory inputs, stress) modifying factors, as well as possible clinical and therapeutic implications.

Neurophysiologic Correlates of Headache Pain in Subjects With Major Depressive Disorder

BACKGROUND

Headache pain is often comorbid with major depressive disorder (MDD) and is associated with greater symptom burden, disability, and suicidality. The biological correlates of headache pain in MDD, however, remain obscure. The purpose of this study was to examine the association between brain oscillatory activity and headache pain in MDD subjects.

METHODS

A total of 64 subjects with MDD who were free of psychoactive medications were evaluated for severity of headache pain in the past week. Brain function was assessed using resting-state quantitative electroencephalography (qEEG). We derived cordance in the theta (4-8 Hz) and alpha (8-12 Hz) frequency bands at each electrode, and examined correlations with headache pain in regions of interest while controlling for depression severity. Frontal and posterior asymmetry in alpha power was calculated in regions of interest.

RESULTS

Headache pain severity was associated with depression severity ( r = 0.447, P < .001). In bilateral frontal and right posterior regions, alpha cordance was significantly associated with headache intensity, including when controlling for depression severity. The direction of the correlation was positive anteriorly and negative posteriorly. Frontal left dominant alpha asymmetry correlated with severity of headache but not depression symptoms.

CONCLUSION

Alterations in brain oscillations identified by alpha cordance and alpha asymmetry may be associated with the pathophysiology of headache pain in depression. These findings should be prospectively confirmed.

Laboratory tests of headache disorders – dawn of a new era?

Context

The classification of headache disorders has improved over the years, but further work is needed to develop and improve headache diagnosis within headache subtypes. The present review is a call for action to implement laboratory tests in the classification and management of primary and some secondary headaches.

Background

In this narrative review we present and discuss published tests that might be useful in phenotyping and/or diagnosis of long-lasting headache disorders such as migraine, tension-type headache, trigeminal autonomic cephalalgias, trigeminal neuralgia and persisting secondary headaches.

Aim

The palpometer test, quantitative sensory testing, nociceptive blink reflex and autonomic tests may be valuable to phenotype and/or diagnose subforms of migraine, tension-type headache, cluster headache, trigeminal neuralgia and medication-overuse headache. Provocation tests with glyceryl trinitrate (GTN) and calcitonin gene-related peptide (CGRP) may be valuable in subclassification of migraine and cluster headache. Lumbar pressure monitoring and optical coherence tomography may valuable tools to diagnose and follow patients with chronic headache and raised intracranial pressure.

Finding

A number of laboratory tests in headache research are presently available, but have primarily been performed in single research studies or a few studies that differ in methods and patient groups. At present, there is no evidence-based strategy for implementing diagnostic tests, but this could be achieved if well-reputed tertiary headache centers commence developing and implementing laboratory tests in order to improve the classification and treatment of headache patients.

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.

Three-dimensional localization of abnormal EEG activity in migraine: a low resolution electromagnetic tomography (LORETA) study of migraine patients in the pain-free interval

Investigating the brain of migraine patients in the pain-free interval may shed light on the basic cerebral abnormality of migraine, in other words, the liability of the brain to generate migraine attacks from time to time. Twenty unmedicated "migraine without aura" patients and a matched group of healthy controls were investigated in this explorative study. 19-channel EEG was recorded against the linked ears reference and was on-line digitized. 60 x 2-s epochs of eyes-closed, waking-relaxed activity were subjected to spectral analysis and a source localization method, low resolution electromagnetic tomography (LORETA). Absolute power was computed for 19 electrodes and four frequency bands (delta: 1.5-3.5 Hz, theta: 4.0-7.5 Hz, alpha: 8.0-12.5 Hz, beta: 13.0-25.0 Hz). LORETA "activity" (=current source density, ampers/meters squared) was computed for 2394 voxels and the above specified frequency bands. Group comparison was carried out for the specified quantitative EEG variables. Activity in the two groups was compared on a voxel-by-voxel basis for each frequency band. Statistically significant (uncorrected P < 0.01) group differences were projected to cortical anatomy. Spectral findings: there was a tendency for more alpha power in the migraine that in the control group in all but two (F4, C3) derivations. However, statistically significant (P < 0.01, Bonferroni-corrected) spectral difference was only found in the right occipital region. The main LORETA-finding was that voxels with P < 0.01 differences were crowded in anatomically contiguous cortical areas. Increased alpha activity was found in a cortical area including part of the precuneus, and the posterior part of the middle temporal gyrus in the right hemisphere. Decreased alpha activity was found bilaterally in medial parts of the frontal cortex including the anterior cingulate and the superior and medial frontal gyri. Neither spectral analysis, nor LORETA revealed statistically significant differences in the delta, theta, and beta bands. LORETA revealed the anatomical distribution of the cortical sources (generators) of the EEG abnormalities in migraine. The findings characterize the state of the cerebral cortex in the pain-free interval and might be suitable for planning forthcoming investigations.

Brainstem auditory-evoked potential habituation and intensity-dependence related to serotonin metabolism in migraine: a longitudinal study

OBJECTIVE

Reduced habituation and increased intensity-dependence of cortical auditory-evoked potentials have been reported in migraine, but it is not known if brainstem mechanisms are chiefly or partly responsible for this hypersensitivity, if brainstem excitability or habituation changes across the migraine cycle, or how excitability relates to symptoms and serotonin metabolism.

METHODS

Brainstem auditory-evoked potentials (BAEPs) to 40, 55, and 70dB binaural rarefaction clicks were recorded in four blocks of 750 stimuli in a blinded longitudinal study in 41 migraine patients. Serotonin was measured in a blood sample from the cubital vein. The test day was classified as baseline, attack, pre-attack or post-attack.

RESULTS

Pre-attack BAEP changes were not found. Wave I, V and interpeak III-V latency increased after the attack. III-V latency correlated with headache history duration and usual headache attack duration. Habituation in wave IV-V dispersion to 40dB was found in controls but not in migraine (p=0.04). Serotonin correlated with BAEP amplitude in controls. Low serotonin correlated with more autonomic symptoms. BAEP intensity-dependence was normal in migraine.

CONCLUSIONS

BAEP latencies, but not amplitude, increase temporarily after a migraine attack. Abnormal habituation of brainstem wave IV-V dispersion in migraine may suggest increased excitation in colliculus inferior at low sound intensities, but no relation to the migraine cycle was found for wave IV-V amplitude, dispersion or habituation. The correlation between BAEP amplitude and serotonin was deranged in migraine patients, but reappeared temporarily within 72h after an attack.

SIGNIFICANCE

No evidence for pre-attack brainstem auditory sensitization was found in migraine. Intensity-dependence of AEP in migraine is probably not a passive reflection of brainstem dysfunction. BAEP changes seem to reflect a slight impact of migraine on serotonergic brainstem pathways.

Electroencephalography in migraine: a review with focus on quantitative electroencephalography and the migraine vs. epilepsy relationship

EEG-studies in migraine in the last decade has contributed modestly to the understanding of headache pathogenesis. Headache patient groups seem to have increased EEG responses to photic stimulation, but a useful biological marker for migraine in single patients has not been found. In future EEG and QEEG studies we recommend to use follow-up designs and record several EEGs across the migraine cycle. It is also important to use a blinded study design in order to avoid selection bias. A clinical EEG should be performed in patients with acute headache attacks when either epilepsy, basilar migraine, migraine with prolonged aura or alternating hemiplegia is suspected. Unequivocal epileptiform abnormalities usually suggest a diagnosis of epilepsy. In children with occipital spike-wave activity the probable diagnosis is childhood epilepsy with occipital paroxysms (CEOP). The final diagnosis of either an epilepsy syndrome or migraine must be mainly based on a clinical judgement [corrected].

Quantitative EEG responses to ischaemic arm stress in migraine

Several studies suggest that patients with migraine respond physiologically to stress differently from controls, yet experimental data are scarce. In order to evaluate the reactivity to stress in migraine, we recorded the quantitative electroencephalogram (qEEG) during non-noxious and noxious ischaemic arm stress in two groups of healthy controls and compared the results with the effects of non-noxious ischaemic arm stress in a group of patients with migraine. In the controls, non-noxious mild stress did not produce any qEEG change but noxious stress induced a significant decrease of the alpha power. By contrast, in migraine patients the non-noxious mild stress was sufficient to induce a significant decrease of the alpha power in all brain regions. The results of our study show that migraine sufferers display a lower threshold to physical stress and confirm previous studies indicating that migraine is a disease characterized by a state of altered neuronal excitability.

Visual Spatial Attention in Migraine Sufferers in Postictal and Interictal Phases: An Event-Related Potential Study

Migraineurs with and without aura (MWAs and MWOAs) as well as controls were measured twice with an interval of 7 days. The first session of recordings and tests for migraineurs was held about 7 hours after a migraine attack. We hypothesized that electrophysiological changes in the posterior cerebral cortex related to visual spatial attention are influenced by the level of arousal in migraineurs with aura, and that this varies over the course of time. ERPs related to the active visual attention task manifested significant differences between controls and both types of migraine sufferers for the N200, suggesting a common pathophysiological mechanism for migraineurs. Furthermore, migraineurs without aura (MWOAs) showed a significant enhancement for the N200 at the second session, indicating the relevance of time of measurement within migraine studies. Finally, migraineurs with aura (MWAs) showed significantly enhanced P240 and P300 components at central and parietal cortical sites compared to MWOAs and controls, which seemed to be maintained over both sessions and could be indicative of increased noradrenergic activity in MWAs.

Visual, long-latency auditory and brainstem auditory evoked potentials in migraine: relation to pattern size, stimulus intensity, sound and light discomfort thresholds and pre-attack state

We aimed to estimate primary sensory evoked potential (EP) amplitude, amplitude-intensity functions and habituation in migraine patients compared with healthy control subjects and to investigate the possible relation to check size, sound and light discomfort thresholds, and the time to the next attack. Amplitudes of cortical visual evoked potentials (VEP, check size 8' and 33'), cortical long latency auditory evoked potential (AEP NIP1; 40, 55 and 70 dB SL tones) and brainstem auditory evoked potential (BAEP wave IV-V; 40, 55 and 65 dB SL clicks) were recorded and analysed in a blind and balanced design. The difference between the response to the first and the second half of the stimulus sequence was used as a measure of habituation. Twenty-one migraine patients (16 women and five men, mean age 39.3 years, six with aura, 15 without aura) and 22 sex- and age-matched healthy control subjects were studied (18 women and four men, mean age 39.5 years). Low sound discomfort threshold correlated significantly with low levels of BAEP wave IV-V amplitude habituation (r = -0.30, P = 0.05). VEP an AEP amplitudes, habituation, and amplitude-intensity function (ASF) slopes did not differ between groups when ANOVA main factors were considered. Control group VEP habituation was found for small check stimuli (P = 0.04), while potentiation was observed for medium sized checks (P = 0.02). The eight migraine patients who experienced headache within 24 h after the test tended to have increased BAEP wave IV-V ASF slopes (P = 0.08). This subgroup did also have a significant VEP habituation to small checks (P = 0.04). No correlation was found between different modalities. These results suggest that: (i) VEP habituation/potentiation state and brainstem activatio state may depend on the attack-interval cycle in migraine; (ii) VEP habituation/ potentiation may depend on spatial stimulus frequency; (iii) phonophobia (and possibly photophobia) may depend more on subcortical (brainstem) function than on cortical mechanisms; (iv) low cortical preactivation in migraine could not be confirmed; (v) EP habituation and ASF analysis may reflect sensory modality-specific, not generalized, central nervous system states in migraine and healthy control subjects.

Migraine in childhood--are periodically occurring migraine attacks related to dynamic changes of cortical information processing?

Amplitudes and habituation of contingent negative variation (CNV) were analyzed in relation to spontaneously occurring migraine attacks in ten children suffering from migraine without aura. Recording took place during feedback training and instrumental conditioning of slow brain potentials. Both the amplitude of the early CNV component and its habituation deficit increase during the 5 days prior to a migraine attack, with maximum abnormalities the day before the ictal episode. Abrupt reduction of the amplitude and normalization of the CNV habituation were observed during the attack. This study provides evidence for neurophysiological periodicity in young migraineurs and emphasizes that the time relative to the migraine attacks must be considered in studies of juvenile migraine during the headache-free period.

Long-term intra-individual variability of the background EEG in normals

OBJECTIVES

Forty-five healthy adult volunteers underwent repeated qEEG examinations with retest intervals 25-62 months in order to investigate the long-term intra-individual variability of several qEEG features such as, absolute and relative power, power asymmetry, coherence, mean and peak frequency and entropy. Prior to any computations all parameters were transformed to Z-scores on the basis of a normal database.

METHODS

Correlation coefficients were used to test the effect of the time on the test-retest differences. Correlation coefficients were also computed between baseline and retest values, as a measure of intra-individual stability, to make our results comparable to most literature data. By computing the standard deviations for test-retest differences, the intra-individual variabilities of the examined parameters were obtained in the unit of inter-individual variability of normal population. The same calculations were carried out with values obtained from the odd and even numbered epochs of the same EEG sections. This way, that portion of the intra-individual variability was estimated that might be introduced even by chance only when the epochs were selected randomly from the same section of EEG conforming to selection criteria.

RESULTS

As for our results, further increase of test-retest differences with time after 25 months might be so insignificant that it could not be demonstrated in our test material. The long-term intra-individual variability for most parameters, especially for total absolute power and alpha mean frequency, was less than the inter-individual variability in the normal population. The moment-to-moment variability was least in the case of the absolute power.

CONCLUSIONS

Estimates for intra-individual variability expressed this way in Z-scores might easily be used in the follow-up of patients even for a few years.

Clinical neurophysiology in childhood headache

Electrophysiological studies in childhood headache are of interest because of the need to make a clinical diagnosis and also because of the efficacy of physiopathological studies in juvenile age attributable to the recent outcome of the illness, with less clinical modification by environmental factors or drug use. Electrophysiological studies in childhood headache are concerned with migraine and electroencephalographic (EEG) evaluations; evoked potentials, event-related potentials and, less often, electromyographic studies are also reported. Visual analysis of EEG suggests an association between migraine and epilepsy; quantitative EEG, visual and event-related evoked potentials show fluctuating abnormalities, depending on the occurrence of the migraine attacks and permanent anomalous patterns related to the basic mechanisms underlying the disease. Blink reflex studies might suggest a primary dysfunction of the nociceptive control central system in children affected by tension-type headache and migraine. The use of neurophysiological procedures in juvenile migraine is considered limited in clinical practice and of particular interest in neurophysiological studies of headache.

EEG spectral analysis in migraine without aura attacks

In 16 patients suffering from migraine without aura, we examined quantitative EEG and steady-state visual evoked potentials (SSVEPs) at 27 Hz stimulation during the critical phase of migraine and in attack-free periods. The main spontaneous EEG abnormalities found during the critical phase were the slowing and asymmetry of the dominant frequency in the alpha range. The amplitude of the SSVEP F1 component was significantly reduced during the attack phase compared with the intercritical phase; in the latter condition the visual reactivity to 27 Hz stimulus was increased over almost the entire scalp compared with normal subjects. The EEG abnormalities confirm a fluctuating modification of alpha activity during the migraine attack, probably related to a functional disorder. The suppression of visual reactivity during the migraine attack could be related to a phenomenon of neuronal depolarization such as spreading depression, occurring in a situation of central neuronal increased excitability predisposing to migraine attacks.

Multichannel visual evoked potentials in migraine

Multichannel recordings of visual evoked potentials (VEPs) have proved to be useful in the evaluation of visual field defects. We studied the topographic distribution of transient VEPs in 15 migraine patients (8 with visual aura and 7 without) and 15 age-matched controls during the migraine-free interval. All the subjects included in the study had normal visual fields. VEPs were recorded from 9 electrodes placed on the posterior scalp. Stimuli were full-field and hemifield reversing square wave grating patterns of medium spatial frequency (4 c/deg). The groups did not show significant differences in latencies and amplitudes of the major components (N70, P100) recorded from the midline. However, migraine patients with visual hemianopic aura showed definite asymmetries in the VEP amplitude distribution. Significantly reduced, absent or polarity-invered VEP responses were recorded ipsilateral to the side of the prodromic visual symptoms. Direct comparison of affected and unaffected hemispheres by partial field stimulation confirmed these findings. According to the VEP cortical generator theory, these abnormalities suggest a functional anomaly consistent with the clinical syndrome and detectable also in the migraine-free interval. None of the migraine patients without aura or the controls showed VEP amplitude asymmetries. We conclude that multichannel VEP recordings may discriminate between different subtypes of migraine and contribute important physiopathological information to the study of this disease.

The value of EEG in children with chronic headaches

To establish the usefulness of electroencephalography (EEG) as a diagnostic tool in the evaluation of headaches in children, we retrospectively reviewed the records of all children referred to our outpatient neuropediatric clinic because of recurrent headaches. Of 312 children, 257 (82%) underwent EEG tracings: 143 of the children who had had EEG recordings were diagnosed as migraineurs. In 31 (12%) of the children, the EEG revealed epileptic activity. The highest incidence of epileptic EEG activity was found amongst the children with very brief headaches. In 22 (8.6%) of the children, diffuse or focal slowing was detected. The group with migraine headache had a significantly higher incidence of slowing than the group with other types of headaches. There was no correlation between focal EEG abnormalities and brain radioimaging studies or clinical course. We conclude that despite the high incidence of epileptic abnormalities, the contribution of EEG to diagnosis and treatment in children with chronic headache is minimal, and should not be routinely prescribed in these children.

EEG features in juvenile migraine: topographic analysis of spontaneous and visual evoked brain electrical activity: a comparison with adult migraine

Topographic analysis of spontaneous and steady-state visual evoked brain electrical activity was carried out between attacks in 82 migraine patients (40 youths and 42 adults). In adult migraine with aura a significant increase of delta rhythm percentage power was observed compared with migraine without aura and age-matched controls. Children suffering from migraine both with aura and without aura had an increased theta rhythm compared to normal controls. The presence of alpha interhemispheric asymmetry discriminated between migraine with aura and without aura, just as in adults. An increased amplitude of the SVEP F1 component with a tendency to the spread of visual reactivity was observed in juvenile migraine with and without aura; this pattern was not dissimilar from the one previously observed in adult migraine with and without aura. Abnormal photic driving in migraine is independent of age and type of migraine.

Human brain measures of clinical pain: a review. I. Topographic mappings

A comprehensive paper (Parts I and II) has been developed to review the cerebral measures employed in studying the brain neurophysiological activities of clinical pain. Part I focuses on the electro-, magnetic-physiological assessment of clinical pain, and Part II concerns the anatomico-, chemical-physiological assessment of clinical pain. In Part I, these measures include the qualitative inspection of the conventional electroencephalogram, quantitative assessment of brain electrical spectral activity through cortical power spectrum density and coherence analyses, and quantitative averaging of cortical electrical or magnetic activities using brain evoked potentials. The mapping and measurement of these electrical activities and magnetic fields are results of recent advent in computer technology and advanced algorithms. Promises and limitations of these topographic measures in understanding pain in the brain are stated. The next article (Part II) of this paper will review tomographic imaging of pain-related brain activities in regional cerebral flow, the scanning of gross and fine brain structures by computerized axial tomography or magnetic resonance imaging, and the imaging and measurement of brain metabolic changes, energy uptake, and receptor bindings through positron emission tomography or single-photon emission computerized tomography. Molecular chemical transformation by the nuclear magnetic resonance analysis of tissue changes and analgesic-receptor interactions will also be noted.

Computerized EEG topography in childhood migraine between and during attacks

Topographic EEG mapping was performed in 58 migrainous children (mean age: 12.9 years; 39 without, 19 with aura) between attacks. Ten children were also recorded during an attack with visual aura. Between attacks there were no significant differences between migraineurs and age-matched controls. During visual aura a decrease in occipital alpha power contralateral to the affected hemifield was found in all patients. This was followed by a bilateral frontal increase in delta power, and, during the headache, by an increased delta activity in posterior-temporal and occipital electrode sites. The possible brain mechanisms underlying these EEG changes are discussed.