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

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.

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.

Resting-state occipital alpha power is associated with treatment outcome in patients with chronic migraine

ABSTRACT

Preventive treatment is crucial for patients with chronic migraine (CM). This study explored the association between resting-state cortical oscillations and 3-month treatment outcome in patients with CM. Treatment-naïve patients with CM were recruited with their demographic data, psychosocial data, and headache profiles as well as the healthy controls (HCs). Resting-state cortical activities were recorded using an electroencephalogram and analysed using source-based and electrode-based spectral power method. The regions of interest were the bilateral primary somatosensory (S1) and visual (V1) cortices. After 3-month treatment with flunarizine, patients with CM were categorized into responders and nonresponders. Demographic, clinical, and electroencephalogram data from 72 patients with CM and 50 HCs were analysed. Elevated anxiety, depression, and stress were observed in patients with CM. Theta power in bilateral S1 and alpha and gamma powers in the right S1 increased in patients with CM. Nonresponders (n = 34) exhibited larger alpha powers in bilateral V1 than those in responders (n = 38). Alpha powers also exhibited significant correlations with changes of monthly headache days. Notably, in responders and nonresponders, occipital alpha powers did not differ at baseline and in the third month. In conclusion, patients with CM who were not responsive to preventive treatment were associated with augmented resting-state occipital alpha activity. Moreover, changes in migraine attack frequency were associated with baseline occipital alpha power. However, the prognostic feature of visual alpha oscillation seems to be inherent because it is not altered by flunarizine treatment. These findings may be useful for developing personalised migraine treatment plans.

Could cathodal transcranial direct current stimulation modulate the power spectral density of alpha-band in migrainous occipital lobe?

OBJECTIVE

To identify the correlation between cathodal transcranial direct current stimulation (tDCS) and the power spectral density (PSD) of alpha-band on the occipital lobe of migraineurs.

METHODS

Firstly, a cross-sectional study was performed to compare the PSD of alpha-band in the occipital cortex of 25 migraineurs versus 10 healthy volunteers in resting state and during repetitive light stimuli (RLS). Secondly, the patients participated in 12 sessions of cathodal (n = 11) or sham tDCS (n = 10) over the primary visual cortex (V1) to investigate the alpha-band PSD.

RESULTS

The alpha-band PSD on the occipital cortex was higher in migraineurs than healthy subjects in resting state and lower during the first train of RLS. Cathodal tDCS over the V1 reduced the alpha-band occipital activity in resting state but did not interfere with the functional responses to RLS when light stimulation was turned on.

CONCLUSIONS

Our findings suggest that the occipital cortex of migraineurs is hypoactive in the baseline condition, but becomes hyperactive when stimulated by light. Cathodal tDCS over the V1 decreases baseline alpha PSD in patients, possibly modulating the involved neuronal circuitries, but it cannot interfere once photic stimulation starts.

Phase clustering in transcranial magnetic stimulation-evoked EEG responses in genetic generalized epilepsy and migraine

BACKGROUND

Epilepsy and migraine are paroxysmal neurological conditions associated with disturbances of cortical excitability. No useful biomarkers to monitor disease activity in these conditions are available. Phase clustering was previously described in electroencephalographic (EEG) responses to photic stimulation and may be a potential epilepsy biomarker.

OBJECTIVE

The objective of this study was to investigate EEG phase clustering in response to transcranial magnetic stimulation (TMS), compare it with photic stimulation in controls, and explore its potential as a biomarker of genetic generalized epilepsy or migraine with aura.

METHODS

People with (possible) juvenile myoclonic epilepsy (JME), migraine with aura, and healthy controls underwent single-pulse TMS with concomitant EEG recording during the interictal period. We compared phase clustering after TMS with photic stimulation across the groups using permutation-based testing.

RESULTS

We included eight people with (possible) JME (five off medication, three on), 10 with migraine with aura, and 37 controls. The TMS and photic phase clustering spectra showed significant differences between those with epilepsy without medication and controls. Two phase clustering-based indices successfully captured these differences between groups. One participant was tested multiple times. In this case, the phase clustering-based indices were inversely correlated with the dose of antiepileptic medication. Phase clustering did not differ between people with migraine and controls.

CONCLUSION

We present methods to quantify phase clustering using TMS-EEG and show its potential value as a measure of brain network activity in genetic generalized epilepsy. Our results suggest that the higher propensity to phase clustering is not shared between genetic generalized epilepsy and migraine.

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.

An update on EEG in migraine

Introduction: In the past few years, brain functional analysis has provided scientific evidence supporting the neuronal basis of migraine. The role of electroencephalography (EEG) in detecting subtle dysfunctions in sensory temporal processing has been fully re-evaluated, thanks to advances in methods of quantitative analysis. However, the diagnostic value of EEG in migraine is very low, and migraine diagnosis is completely based on clinical criteria, while the utility of EEG in migraine pathophysiology has only been confirmed in more recent applications. Areas covered: The present review focuses on the few situations in which EEG may provide diagnostic utility, and on the numerous and intriguing applications of novel analysis, based on time-related changes in neuronal network oscillations and functional connectivity. Expert opinion: Although routine EEG is not particularly useful for the clinical assessment of migraine, novel methods of analysis, mostly based on functional connectivity, could improve knowledge of the migraine brain. The application is worthy of promotion and improvement in support of neuroimaging data to shed light on migraine mechanisms and support the rationale for therapeutic approaches.

Improving the quality of a collective signal in a consumer EEG headset

This work focuses on the experimental data analysis of electroencephalography (EEG) data, in which multiple sensors are recording oscillatory voltage time series. The EEG data analyzed in this manuscript has been acquired using a low-cost commercial headset, the Emotiv EPOC+. Our goal is to compare different techniques for the optimal estimation of collective rhythms from EEG data. To this end, a traditional method such as the principal component analysis (PCA) is compared to more recent approaches to extract a collective rhythm from phase-synchronized data. Here, we extend the work by Schwabedal and Kantz (PRL 116, 104101 (2016)) evaluating the performance of the Kosambi-Hilbert torsion (KHT) method to extract a collective rhythm from multivariate oscillatory time series and compare it to results obtained from PCA. The KHT method takes advantage of the singular value decomposition algorithm and accounts for possible phase lags among different time series and allows to focus the analysis on a specific spectral band, optimally amplifying the signal-to-noise ratio of a common rhythm. We evaluate the performance of these methods for two particular sets of data: EEG data recorded with closed eyes and EEG data recorded while observing a screen flickering at 15 Hz. We found an improvement in the signal-to-noise ratio of the collective signal for the KHT over the PCA, particularly when random temporal shifts are added to the channels.

Altered processing of sensory stimuli in patients with migraine

Migraine is a cyclic disorder, in which functional and morphological brain changes fluctuate over time, culminating periodically in an attack. In the migrainous brain, temporal processing of external stimuli and sequential recruitment of neuronal networks are often dysfunctional. These changes reflect complex CNS dysfunction patterns. Assessment of multimodal evoked potentials and nociceptive reflex responses can reveal altered patterns of the brain's electrophysiological activity, thereby aiding our understanding of the pathophysiology of migraine. In this Review, we summarize the most important findings on temporal processing of evoked and reflex responses in migraine. Considering these data, we propose that thalamocortical dysrhythmia may be responsible for the altered synchronicity in migraine. To test this hypothesis in future research, electrophysiological recordings should be combined with neuroimaging studies so that the temporal patterns of sensory processing in patients with migraine can be correlated with the accompanying anatomical and functional changes.

Functional and effective connectivity in EEG alpha and beta bands during intermittent flash stimulation in migraine with and without aura

Objectives:

This research was a case-control study to evaluate functional and effective connectivity patterns in ongoing electroencephalography (EEG) under repetitive photic stimulation in the interictal phase of migraine patients with and without aura compared to nonmigraine controls.

Methods:

EEG was recorded by six scalp electrodes from 19 migraine without aura patients (MO), 19 migraine with aura patients (MA) and 11 healthy subjects (control group (N)). Flash stimuli were presented at 9–27 Hz frequencies. Phase synchronization after Hilbert transform and Granger causality were evaluated filtering the EEG in alpha and beta bands.

Results:

Phase synchronization increased in alpha band in MO, and decreased in beta band in MA, with respect to controls. The intensity of directed interactions in beta band, revealed by Granger causality, increased in MA compared to both MO patients and controls.

Discussion:

There were clear differences in ongoing EEG under visual stimulation, which emerged between the two forms of migraine, probably subtended by increased cortical activation in migraine with aura, and compensatory phenomena of reduced connectivity and functional networks segregation, occurring in patients not experiencing aura symptoms. Further investigation may confirm whether the clinical manifestation of aura symptoms is subtended by a peculiar neuronal connectivity pattern.

Habituation of steady-state visual evoked potentials in response to high-frequency polychromatic foveal visual stimulation

In an attempt to develop safe and robust methods for monitoring migraineurs' brain states, we explores the feasibility of using white, red, green and blue LED lights flickering around their critical flicker fusion (CFF) frequencies as foveal visual stimuli for inducing steady-state visual evoked potentials (SSVEP) and causing discernible habituation trends. After comparing the habituation indices, the multi-scale entropies and the time dependent intrinsic correlations of their SSVEP signals, we reached a tentative conclusion that sharp red and white light pulses flickering barely above their CFF frequencies can replace commonly used 13Hz stimuli to effectively cause SSVEP habituation among normal subjects. Empirical results showed that consecutive short bursts of light can produce more consistent responses than a single prolonged stimulation. Since these high frequency stimuli do not run the risk of triggering migraine or seizure attacks, further tests of these stimuli on migraine patients are warranted in order to verify their effectiveness.

Pain relief by transcutaneous electric nerve stimulation with bidirectional modulated sine waves in patients with chronic back pain: a randomized, double-blind, sham-controlled study

Objectives.  Newly developed bidirectional modulated sine waves (BMW) might provide some derived benefit to patients with low back pain. Pain relief by transcutaneous electric nerve stimulation (TENS) with BMWs was tested. Materials and Methods.  Analgesic effects of BMWs and conventional bidirectional pulsed waves on chronic back pain in 28 patients were compared, and effects of repeated TENS using BMWs on chronic back pain were investigated in 21 patients by means of a randomized double-blind, sham-controlled, parallel-group method. Pain intensity was assessed using numerical rating scale (NRS). Results.  There was significant immediate reduction in NRS in patients receiving BMWs, and 60 min after treatment compared to sham TENS. Weekly repeated treatments using massage and TENS with BMWs for 5 weeks resulted in a decrease of NRS, but there were no significant differences between the TENS plus massage and sham TENS plus massage groups. Conclusions.  This study shows that TENS with BMWs significantly inhibits chronic back pain, and treatment effects are attained within a day. The results also suggest that there were no statistically significant long-term effects of TENS with BMW in the repeated treatment.

Electroencephalogram variations in pediatric migraines and tension-type headaches

This study evaluates specific electroencephalogram abnormalities in pediatric migraine and tension-type headaches, and demonstrates the clinical value of these abnormalities. We studied 50 migraine patients and 50 tension-type headache patients. Their mean age ± SD was 10.62 ± 3.21 (range, 5-16) years in the migraine group, and 13.00 ± 2.37 (7-16) years in the tension-type headache group. Diagnoses were rendered according to the International Classification of Headache Disorders, 2nd Edition, First Revision, of the International Headache Society. All patients underwent two waking-state electroencephalograms, one during a headache, and the other when headache-free. Thirty-six percent (18/50) of migraine patients and 12% (6/50) of tension-type headache patients revealed specific electroencephalogram abnormalities in headache attack electroencephalograms (P < 0.05). In headache-free period electroencephalograms, 16% (8/50) of the migraine group and 2% (1/50) of the tension-type headache group revealed abnormalities (P < 0.05). Our results indicate that electroencephalogram abnormalities are particularly prevalent in migraines, especially during headache attacks. This study is the first, to the best of our knowledge, on electroencephalographic evaluation of pediatric migraine and tension-type headache patients during both headache attacks and headache-free periods.

Spatial frequency differentially affects habituation in migraineurs: a steady-state visual-evoked potential study

A lack of habituation in visual-evoked potentials (VEPs) is the main abnormality observed in migraineurs. However, no study of steady-state VEPs has yet evaluated pattern-reversal stimuli with respect to habituation behavior or spatial frequency. The aim of this study was to clarify habituation behavior in migraineurs between attacks and to establish characteristics of VEPs in these patients. Steady-state VEPs were sequentially recorded as checkerboard patterns in four consecutive blocks from 12 patients with migraine without aura (MO), 12 patients with migraine with aura (MA), and 12 healthy controls (HC) at four spatial frequencies of 0.5, 1.0, 2.0, and 4.0 cycles per degree (cpd) with a stimulus rate of 7.5 Hz (15 reversal/s). VEP amplitudes were consistently higher in migraineurs. However, habituation was not demonstrated in HCs, and migraineurs did not reveal a clear lack of habituation. MAs exhibited high-amplitude VEPs, depending on spatial frequency. In the MA patients, amplitude differences reached statistical significance at 2.0 cpd. The sequential amplitude changes at 0.5 cpd were significantly different in MAs compared with HCs. Migraine patients exhibited high-amplitude VEPs, which were dependent on spatial frequency, and may be related to altered excitability in pre-cortical and cortical visual processing.

Analysis of repetitive flash stimulation frequencies and record periods to detect migraine using artificial neural network

Different kind of methods has been applied to detect the migraine by using flash stimulation. Especially frequency analysis of EEG signal is the most preferred method to detect the migraine by using flash stimulation. Different flash stimulation frequencies at wide frequency range have been used in migraine detection. But the effects of these flash stimulation frequencies and the most effective frequency can be determined by analyzing these frequencies separately. Since each stimulation frequency has been implemented in different time periods, it is necessary to determine the time period to detect magnitude increase in migraine patients. The aim of this study is to determine the most effective flash stimulation frequency and time duration to detect the migraine. In this study, we analyzed the flash stimulation frequencies and time duration separately for detecting migraine. Performance of each flash stimulation frequency has been determined to detect the migraine by analyzing the power spectrums obtained under 2 Hz, 4 Hz and 6 Hz and artificial neural network has been used to determine the which data has a superior performance. Afterwards we analyzed the 2 s, 4 s, 6 s, 8 s and 10 s of flash stimulation periods separately by observing the power spectrums and the results are verified by using artificial neural network. As a result of this study we proposed the 4 Hz of flash stimulation frequency is the most effective frequency and 8 s time period is necessary to detect the migraine at the beta band of EEG's T5-T3 channel.

Abnormal visual processing in migraine with aura: a study of steady-state visual evoked potentials

BACKGROUND

Although a number of studies reported different interictal findings between migraine with aura (MA) and migraine without aura (MO), the pathophysiology of the visual aura in migraine remains unclear.

OBJECTIVE

To investigate the visual processing in patients who experience MA between attacks using steady-state visual evoked potentials (SSVEPs).

METHODS

SSVEPs to high (98%) and low (29%) contrast black and white checkerboard gratings with two spatial frequencies (0.5 and 2.0 cpd) at 5 and 10 Hz (10 and 20 reversal/s) were recorded binocularly from 10 patients with MA, 10 patients with MO between attacks and 20 healthy controls (HC). The SSVEPs were Fourier analyzed to obtain the amplitude and phase of the second (2F) and fourth (4F) harmonic response.

RESULTS

In the amplitude of 2F, at 0.5 cpd, there was significant increased amplitude in both MA and MO in comparison to HC at 5 Hz in high and low contrast. However, no significant differences were detected at 2.0 cpd in both 5 and 10 Hz in high and low contrast. In the amplitude of 4F, at 2.0 cpd, there was significant increased amplitude in MA in comparison to MO and HC at 10 Hz in high contrast. However, there were no significant differences at 0.5 cpd at both 5 and 10 Hz in high and low contrast. There were no significant phase differences between MA, MO, and HC.

CONCLUSION

The high amplitude of the SSVEPs suggests that interictally migraine patients have abnormal excitability in the primary visual cortex, and this change in excitability may exist, at least partially, in the visual association cortex in MA.

Migraine detection through spontaneous EEG analysis

Spontaneous EEG patterns are studied to detect migraine patients both during the attack and in headache-free periods. The EEG signals are analyzed through the wavelets and both scale-dependent and scale-independent features are computed to characterize the patterns. The classification is carried out by a supervised neural network. The efficiency of the method is evaluated through the Receiver Operating Characteristic (ROC) analysis and the Wilcoxon-Mann-Whitney (WMW) test. Although a high discrimination is observed with one single neural output, a complete separation among MwA patients and healthy subjects is obtained when a scatter plot is drawn in the plane of two suitable neural outputs.

Effects of levetiracetam vs topiramate and placebo on visually evoked phase synchronization changes of alpha rhythm in migraine

OBJECTIVE

Recent theories about migraine pathogenesis have outlined an abnormal central processing of sensory signals, also suggested by an abnormal pattern of EEG hyper-synchronization under visual stimulation. The aim of the present study was to test the efficacy of topiramate and levetiracetam vs placebo in a double blind project observing the effects of the three treatments on the EEG synchronization in the alpha band under sustained flash stimulation.

METHODS

Forty-five migraine without aura outpatients (MO) were selected and randomly assigned to 100mg topiramate, 1000 mg levetiracetam or placebo treatment. In addition, 24 non-migraine healthy controls were submitted to EEG analysis. The EEG was recorded by 19 channels: flash stimuli with a luminosity of 0.2J were delivered, in a frequency range from 3 to 30 Hz. We evaluated the phase synchronization index, that we previously applied in migraine, after EEG signals filtering in the alpha band. Our approach was based on the Hilbert transform.

RESULTS

Both levetiracetam and topiramate significantly decreased migraine frequency, compared with placebo. MO patients displayed increased alpha-band phase synchronization as an effect of stimulus frequency; on the other hand the stimuli had an overall desynchronizing effect on control subjects. The phase synchronization index separates the two stages, before and after the treatment, only for levetiracetam, at stimulus frequencies of 9, 18, 24 and 27 Hz.

CONCLUSIONS

An abnormal alpha band synchronization under visual stimuli was confirmed in migraine; this phenomenon was reversed by levetiracetam preventive treatment.

SIGNIFICANCE

These results confirmed in humans the inhibiting action of levetiracetam on neuronal hyper-synchronization.