Topographic analysis of steady-state visual evoked potentials (SVEPs) in the medium frequency range in migraine with and without aura

Bi-sinusoidal light stimulation reveals an enhanced response power and reduced phase coherence at the visual cortex in migraine

Introduction

Migraine is associated with enhanced visual sensitivity during and outside attacks. Processing of visual information is a highly non-linear process involving complex interactions across (sub)cortical networks. In this exploratory study, we combined electroencephalography with bi-sinusoidal light stimulation to assess non-linear features of visual processing in participants with migraine.

Methods

Twenty participants with migraine (10 with aura, 10 without aura) and ten non-headache controls were measured (outside attacks). Participants received bi-sinusoidal 13 + 23 Hz red light visual stimulation. Electroencephalography spectral power and multi-spectral phase coherence were compared between groups at the driving stimulation frequencies together with multiples and combinations of these frequencies (harmonic and intermodulation frequencies) caused by non-linearities.

Results

Only at the driving frequency of 13 Hz higher spectral power was found in migraine with aura participants compared with those with migraine without aura and controls. Differences in phase coherence were present for 2nd, 4th, and 5th-order non-linearities in those with migraine (migraine with and without aura) compared with controls. Bi-sinusoidal light stimulation revealed evident non-linearities in the brain's electroencephalography response up to the 5th order with reduced phase coherence for higher order interactions in interictal participants with migraine.

Discussion

Insight into interictal non-linear visual processing may help understand brain dynamics underlying migraine attack susceptibility. Future research is needed to determine the clinical value of the results.

Persistent post-traumatic headache: a migrainous loop or not? The clinical evidence

BACKGROUND

Headache is a common complication of traumatic brain injury. The International Headache Society defines post-traumatic headache as a secondary headache attributed to trauma or injury to the head that develops within seven days following trauma. Acute post-traumatic headache resolves after 3 months, but persistent post-traumatic headache usually lasts much longer and accounts for 4% of all secondary headache disorders.

MAIN BODY

The clinical features of post-traumatic headache after traumatic brain injury resemble various types of primary headaches and the most frequent are migraine-like or tension-type-like phenotypes. The neuroimaging studies that have compared persistent post-traumatic headache and migraine found different structural and functional brain changes, although migraine and post-traumatic headache may be clinically similar. Therapy of various clinical phenotypes of post-traumatic headache almost entirely mirrors the therapy of the corresponding primary headache and are currently based on expert opinion rather than scientific evidence. Pharmacologic therapies include both abortive and prophylactic agents with prophylaxis targeting comorbidities, especially impaired sleep and post-traumatic disorder. There are also effective options for non-pharmacologic therapy of post-traumatic headache, including cognitive-behavioral approaches, onabotulinum toxin injections, life-style considerations, etc. CONCLUSION: Notwithstanding some phenotypic similarities, persistent post-traumatic headache after traumatic brain injury, is considered a separate phenomenon from migraine but available data is inconclusive. High-quality studies are further required to investigate the pathophysiological mechanisms of this secondary headache, in order to identify new targets for treatment and to prevent disability.

Clinical neurophysiology of migraine with aura

BACKGROUND

The purpose of this review is to provide a comprehensive overview of the findings of clinical electrophysiology studies aimed to investigate changes in information processing of migraine with aura patients.

MAIN BODY

Abnormalities in alpha rhythm power and symmetry, the presence of slowing, and increased information flow in a wide range of frequency bands often characterize the spontaneous EEG activity of MA. Higher grand-average cortical response amplitudes, an increased interhemispheric response asymmetry, and lack of amplitude habituation were less consistently demonstrated in response to any kind of sensory stimulation in MA patients. Studies with single-pulse and repetitive transcranial magnetic stimulation (TMS) have reported abnormal cortical responsivity manifesting as greater motor evoked potential (MEP) amplitude, lower threshold for phosphenes production, and paradoxical effects in response to both depressing or enhancing repetitive TMS methodologies. Studies of the trigeminal system in MA are sparse and the few available showed lack of blink reflex habituation and abnormal findings on SFEMG reflecting subclinical, probably inherited, dysfunctions of neuromuscular transmission. The limited studies that were able to investigate patients during the aura revealed suppression of evoked potentials, desynchronization in extrastriate areas and in the temporal lobe, and large variations in direct current potentials with magnetoelectroencephalography. Contrary to what has been observed in the most common forms of migraine, patients with familial hemiplegic migraine show greater habituation in response to visual and trigeminal stimuli, as well as a higher motor threshold and a lower MEP amplitude than healthy subjects.

CONCLUSION

Since most of the electrophysiological abnormalities mentioned above were more frequently present and had a greater amplitude in migraine with aura than in migraine without aura, neurophysiological techniques have been shown to be of great help in the search for the pathophysiological basis of migraine aura.

Avaliação da sensibilidade ao contraste em pacientes com migrânea

O objetivo foi medir a Função de Sensibilidade ao Contraste (FSC) de pacientes com migrânea e de voluntários saudáveis sem a patologia. Participaram dos testes 12 voluntários do sexo feminino, seis com migrânea e seis sem migrânea na faixa etária de 20 a 37 anos. As medidas de FSC foram realizadas utilizando estímulos visuais estáticos de grades senoidais angulares com frequências espaciais de 2, 3, 4, 24 e 64 ciclos/360º Foi utilizado o método psicofísico da escolha forçada entre duas alternativas temporais, condições de luminância fotópica (luminância média da tela de 41 cd/m²) e visão binocular com pupila natural. Os resultados demonstram que a percepção visual de contraste dos voluntários com migrânea foi menor nas frequências de 2, 3, 4 e 64 ciclos/360º. Esses achados preliminares sugerem alterações na FSC relacionadas a essa patologia.

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.

The brain is hyperexcitable in migraine

Migraine is a very common disorder occurring in 20% of women and 6% of men. Central neuronal hyperexcitability is proposed to be the putative basis for the physiological disturbances in migraine. Since there are no consistent structural disturbances in migraine, physiological and psychophysical studies have provided insight into the underlying mechanisms. This is a review of the neurophysiological studies which have provided an insight to migraine pathogenesis supporting the theory of hyperexcitability.

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 contrast processing in migraine

Some migraine sufferers report certain visual patterns can reliably trigger a migraine attack, such as high contrast striped patterns or flickering lights. Differences between people with and without migraine on tasks that involve these patterns have been attributed to abnormal cortical processing in migraine, although the locus and extent of the abnormality remains unclear, as is any relationship between impairment on various visual tasks. In this study 58 migraine sufferers and 61 control subjects participated in three visual tasks involving striped patterns. One assessed pattern sensitivity with high contrast patterns, the second detection thresholds for low contrast patterns and the third supra-threshold contrast scaling. With each measure, the performance of migraine sufferers as a group differed to the performance of non-migraine control subjects. There were no significant differences between the migraine subgroups when classified according to the presence or absence of aura. Cross-correlating the results from the three tasks, however, revealed consistent associations: impaired or extreme responses on one task were associated with impaired or extreme responses on the others. There were no overall effects due to migraine duration, the frequency of migraine attacks or the time since the last attack. These results are discussed in the context of visually induced migraine, proposed causes of abnormal cortical function in migraine and the prospects for developing clinically useful tests of visual function.

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.

Steady-state visual-evoked potentials in headache: diagnostic value in migraine and tension-type headache patients

We tested the hypothesis that migraine and tension-type headache are separate disorders based on visual evoked potentials. We recruited 120 migraine without aura patients (MwoA), 64 tension-type headache patients (TTH), and 51 healthy controls. We performed discriminant analysis combined with a stepwise selection of predictors. Mean values of the F1 component were significantly increased over Fp1, C3, P4, O2 and O1 electrodes in MwoA and TTH patients compared with normal subjects. Only the control subjects were correctly distinguished. The increased brain response to visual stimulation detected in both MwoA and TTH may suggest a common neuronal dysfunction in the two headache subtypes.

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.

Photic driving in migraine: correlations with clinical features

Fifty-eight migraineurs were studied by intermediate frequency steady-state visual evoked potentials (SSVEPs) during headache-free periods. Sex, age, age of onset of migraine, duration of illness, type of migraine, side of pain, sleep-wake disorders, and frequency of migraine attacks did not correlate with any SSVEP abnormalities. On the other hand, visual responsiveness was significantly increased in subjects with family history of migraine, and in those with autonomic symptoms. Our results may indicate that a genetic predisposition to migraine underlies the observed abnormal visual response in migraineurs.

Pattern reversal visual evoked potentials in children with migraine or tension-type headache

Pattern reversal visual evoked potentials were recorded in 71 children with different types of migraine (e.g. migraine with aura, migraine without aura) or tension-type headache and in 19 controls (mean age of both groups 9 years). P100 latencies were comparable in all three groups.