Potentiation instead of habituation characterizes visual evoked potentials in migraine patients between attacks

No Evidence of Cross-Orientation Suppression Differences in Migraine with Aura Compared to Healthy Controls

It has been suggested that there may be an imbalance of excitation and inhibitory processes in the visual areas of the brain in people with migraine aura (MA). One idea is thalamocortical dysrhythmia, characterized by disordered oscillations, and thus disordered communication between the lateral geniculate nucleus and the cortex. Cross-orientation suppression is a visual task thought to rely on inhibitory processing, possibly originating in the lateral geniculate nucleus. We measured both resting-state oscillations and cross-orientation suppression using EEG over occipital areas in people with MA and healthy volunteers. We found evidence of cross-orientation suppression in the SSVEP responses, but no evidence of any group difference. Therefore, inhibitory processes related to cross-orientation suppression do not appear to be impaired in MA.

What's in a Name? Chronic Vestibular Migraine or Persistent Postural Perceptual Dizziness?

Current consensus diagnostic criteria for vestibular migraine (VM) describes this as an episodic disorder. However, a minority of patients report prolonged (>72 h duration) or even persistent VM symptoms, prompting whether a chronic variant of vestibular migraine (CVM) should be introduced to the current classification and how best to define it. Here we summarize current evidence of such a potential chronic variant of VM and critically review proposed definitions for CVM. Potential approaches to establish a diagnostic framework for CVM include (a) following the distinction between episodic and chronic migraine headaches, namely, frequent and/or prolonged episodes of VM (but not persistent vertigo or dizziness) in the context of chronic migraine headaches or (b) daily dizzy spells over more than 6 months that responded well to prophylactic anti-migraine therapy. A key challenge when defining diagnostic criteria for CVM is how to distinguish it from other chronic vestibular syndromes such as motion sickness, persistent postural-perceptual dizziness (PPPD), and mal de débarquement syndrome. Indeed, more than 50% of patients with PPPD and up to 46% with mal de débarquement syndrome fulfil diagnostic criteria for episodic migraine headaches, suggesting these disorders may all lie along a spectrum. We propose that when VM becomes persistent, it is best classified as PPPD but that VM and PPPD are not mutually exclusive, such that patients with PPPD need not have features of VM, and the triggering event for persistent dizziness may be independent of migraine. However, further research is needed to better characterize the spectrum of clinical phenotypes in patients with chronic dizziness, migraine headaches and anxiety, to define whether a chronic variant of VM sufficiently differs from current persistent dizziness definitions.

Prospective Matched Case-Control Study of Over-Early P100 Wave Latency in Migraine with Aura

A sizable portion of the world's population suffers from migraines with aura. The purpose of this research is to describe the findings of a case-control study that was carried out to gain a better understanding of how migraine with aura manifests. The research looked at the P100 delay of the visual-evoked potential in both eyes of 92 healthy people and 44 patients who suffered from migraines with visual aura. All of the participants in the study were recruited from King Fahad University Hospital in Saudi Arabia. Both sets of people had the same ancestry and originated from the same location. Patients who suffered from migraines with aura exhibited a significantly shorter P100 delay in both eyes compared to healthy controls (p = 0.001), which is evidence that their early visual processing was distinct. In order to arrive at these findings, we compared people who suffer from migraines with aura to people who do not suffer from migraines and used them as subjects. These findings contribute to the ongoing attempts to bring the disease under control and provide vitally significant new information regarding the functioning of headaches with auras. The primary focus of study in the future should be on determining the nature of the connection between issues with early visual processing and headaches with aura.

Exaggerated response to pattern reversal visual evoked potential among migraineurs

OBJECTIVE

Visual evoked potential recording has reported ambiguous results among migraineurs, thus the present study explored the association of check-size and reversal rates on the latency and amplitude of pattern reversal VEP among migraineurs.

METHOD AND MATERIAL

Monocular VEP responses for both eyes were recorded in 133 migraineurs and 111 controls. Checkerboard pattern with phase reversal frequency of 0.5, 1, 2 and 4 Hz and check-size of 16 × 16, 32 × 32, 64 × 64 and 128 × 128, i.e. spatial frequency of 0.475, 1.029, 2.056 and 4.112 cycle per degree (cpd) were used to record 100 responses each. Three-minutes gap was given after change of reversal frequency to a higher rate for next cycle of 4 check-size records.

RESULT

A linear increase in latencies was observed with decreasing check-size in both groups, but migraineurs had significantly higher latencies at a given reversal rate. Amplitudes A1 and A2 were higher among migraineurs and amplitude A2 showed an inverted 'U' shaped trend with maximum amplitude at 32 × 32 check size (1.029 cpd) in both groups, with an exaggerated response among migraineurs. Check-size 32 × 32 i.e. spatial frequency of 1.029 behaves differently than other larger or smaller check-sizes.

CONCLUSION

Variable VEP response for different visual stimuli may be due to differential activation of respective retinocortical pathways and cortical areas. The highest amplitude at modest check-size suggests a contributory role of foveal-parafoveal fibres in migraineurs. Exaggerated physiological response to visual stimuli may be responsible for higher amplitudes and prolonged latencies among migraineurs.

Exploring sensory sensitivity, cortical excitability, and habituation in episodic migraine, as a function of age and disease severity, using the pattern-reversal task

BACKGROUND

Migraine is a cyclic, neurosensory disorder characterized by recurrent headaches and altered sensory processing. The latter is manifested in hypersensitivity to visual stimuli, measured with questionnaires and sensory thresholds, as well as in abnormal cortical excitability and a lack of habituation, assessed with visual evoked potentials elicited by pattern-reversal stimulation. Here, the goal was to determine whether factors such as age and/or disease severity may exert a modulatory influence on sensory sensitivity, cortical excitability, and habituation.

METHODS

Two similar experiments were carried out, the first comparing 24 young, episodic migraine patients and 28 healthy age- and gender-matched controls and the second 36 middle-aged, episodic migraine patients and 30 healthy age- and gender-matched controls. A neurologist confirmed the diagnoses. Migraine phases were obtained using eDiaries. Sensory sensitivity was assessed with the Sensory Perception Quotient and group comparisons were carried out. We obtained pattern-reversal visual evoked potentials and calculated the N1-P1 Peak-to-Peak amplitude. Two linear mixed-effects models were fitted to these data. The first model had Block (first block, last block) and Group (patients, controls) as fixed factors, whereas the second model had Trial (all trials) and Group as fixed factors. Participant was included as a random factor in both. N1-P1 first block amplitude was used to assess cortical excitability and habituation was defined as a decrease of N1-P1 amplitude across Blocks/Trials. Both experiments were performed interictally.

RESULTS

The final samples consisted of 18 patients with episodic migraine and 27 headache-free controls (first experiment) and 19 patients and 29 controls (second experiment). In both experiments, patients reported increased visual hypersensitivity on the Sensory Perception Quotient as compared to controls. Regarding N1-P1 peak-to-peak data, there was no main effect of Group, indicating no differences in cortical excitability between groups. Finally, significant main effects of both Block and Trial were found indicating habituation in both groups, regardless of age and headache frequency.

CONCLUSIONS

The results of this study yielded evidence for significant hypersensitivity in patients but no significant differences in either habituation or cortical excitability, as compared to headache-free controls. Although the alterations in patients may be less pronounced than originally anticipated they demonstrate the need for the definition and standardization of optimal methodological parameters.

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.

Topographic localization of migraine triggers and its association with headache frequency and severity

OBJECTIVE

Internal biological rhythm with or without external trigger may precipitate migraine. Classifying exogenous and endogenous triggers to a topographic localization may help in understanding the migraine. We report topographic localization of migraine triggers and its influence on headache frequency and severity.

METHODS

588 migraineurs, aged 16-69 years were included. Various endogenous and exogenous triggers were categorized to topographic localization- hypothalamic, pituitary, auditory, visual, somato-sensory, olfactory and gustatory. The relationship of topographic localization of triggers with episodic versus chronic migraine, and moderate versus severe headache were analyzed using univariate followed by multivariate analysis.

RESULTS

All migraineurs had triggers 584(99.9%) except 4(0.1%) patients. Presence of multiple triggers (99.4%), and combination of both endogenous and exogenous triggers (97.7%) was the rule. On topographic localization, hypothalamic trigger was the commonest (98.1%) followed by visual (84.1%), auditory (82.1%), somatosensory (76.1%), olfactory (26.2%), pituitary (24.1%), and gustatory (6.6%). 98.6% patients had combination of hypothalamic with pituitary triggers. Hypothalamic [Adjusted odds ratio (AOR) 4.50] and auditory triggers (AOR 0.34) independently predicted chronic migraine, and auditory (AOR 0.55) and gustatory (AOR 2.41) triggers predicted severity of headache.

CONCLUSION

Hypothalamic triggers are the commonest suggesting an innate susceptibility of migraine. Auditory trigger may precipitate frequent and severe headache.

What has neurophysiology revealed about migraine and chronic migraine?

Since the first electroencephalographic recordings obtained by Golla and Winter in 1959, researchers have used a variety of neurophysiological techniques to determine the mechanisms underlying recurrent migraine attacks. Neurophysiological methods have shown that the brain during the interictal phase of an episodic migraine is characterized by a general hyperresponsiveness to sensory stimuli, a malfunction of the monoaminergic brainstem circuits, and by functional alterations of the thalamus and thalamocortical loop. All of these alterations vary plastically during the phases of the migraine cycle and interictally with the days following the attack. Both episodic migraineurs recorded during an attack and chronic migraineurs are characterized by a general increase in the cortical amplitude response to peripheral sensory stimuli; this is an electrophysiological hallmark of a central sensitization process that is further reinforced through medication overuse. Considering the large-scale functional involvement and the main roles played by the brainstem-thalamo-cortical network in selection, elaboration, and learning of relevant sensory information, future research should move from searching for one specific primary site of dysfunction at the macroscopic level, to the chronic, probably genetically determined, molecular dysfunctions at the synaptic level, responsible for short- and long-term learning mechanisms.

Lack of Habituation in Migraine Patients Based on High-Density EEG Analysis Using the Steady State of Visual Evoked Potential

Migraine is a periodic disorder in which a patient experiences changes in the morphological and functional brain, leading to the abnormal processing of repeated external stimuli in the inter-ictal phase, known as the habituation deficit. This is a significant feature clinically of migraine in both two types with aura or without aura and plays an essential role in studying pathophysiological differences between these two groups. Several studies indicated that the reason for migraine aura is cortical spreading depression (CSD) but did not clarify its impact on migraine without aura and lack of habituation. In this study, 22 migraine patients (MWA, N = 13), (MWoA, N = 9), and healthy controls (HC, N = 19) were the participants. Participants were exposed to the steady state of visual evoked potentials also known as (SSVEP), which are the signals for a natural response to the visual motivation at four Hz or six Hz for 2 s followed by the inter-stimulus interval that varies between 1 and 1.5 s. The order of the temporal frequencies was randomized, and each temporal frequency was shown 100 times. We recorded from 128 customized electrode locations using high-density electroencephalography (HD-EEG) and measured amplitude and habituation for the N1-P1 and P1-N2 from the first to the sixth blocks of 100 sweep features in patients and healthy controls. Using the entropy, a decrease in amplitude and SSVEP N1-P1 habituation between the first and the sixth block appeared in both MWA and MWoA (p = 0.0001, Slope = -0.4643), (p = 0.065, Slope = 0.1483), respectively, compared to HC. For SSVEP P1-N2 between the first and sixth block, it is varied in both MWA (p = 0.0029, Slope = -0.3597) and MWoA (p = 0.027, Slope = 0.2010) compared to HC. Therefore, migraine patients appear amplitude decrease and habituation deficit but with different rates between MWA, and MWoA compared to HCs. Our findings suggest this disparity between MWoA and MWA in the lack of habituation and amplitude decrease in the inter-ictal phase has a close relationship with CSD. In light of the fact that CSD manifests during the inter-ictal phase of migraine with aura, which is when migraine seizures are most likely to occur, multiple researchers have lately reached this conclusion. This investigation led us to the conclusion that CSD during the inter-ictal phase and migraine without aura are associated. In other words, even if previous research has not demonstrated it, CSD is the main contributor to both types of migraine (those with and without aura).

Cerebrovascular reactivity and deep white matter hyperintensities in migraine: A prospective CO2 targeting study

Several studies suggested the association of migraine with deep white matter hyperintensities (WMHs). We aimed to explore the cerebrovascular reactivity (CVR), deep WMH burden, and their association in patients with migraine using a state-of-the-art methodology. A total of 31 patients with migraine without aura and 31 age/sex-matched controls underwent 3T MRI with prospective end-tidal carbon dioxide (CO₂) targeting. We quantified deep WMH clusters using an automated segmentation tool and measured voxel-wise CVR by changes in blood oxygen level-dependent signal fitted to subjects' end-tidal CO₂. The association of migraine and CVR with the presence of WMH in each voxel and interaction of migraine and CVR on WMH were analysed. Patients had a higher number of deep WMHs than controls (p = 0.015). Migraine and reduced CVR were associated with increased probability of having WMHs in each voxel (adjusted OR 30.78 [95% CI 1.89-500.53], p = 0.016 and adjusted OR 0.30 [0.29-0.32], p < 0.001, respectively). Migraine had an effect modification on CVR on deep WMHs (p for interaction <0.001): i.e. the association between CVR and WMH was greater in patients than in controls. We suggest that the migraine-WMH association can be explained by the effect modification on the CVR.

Genetics, molecular control and clinical relevance of habituation learning

Habituation is the most fundamental form of learning. As a firewall that protects our brain from sensory overload, it is indispensable for cognitive processes. Studies in humans and animal models provide increasing evidence that habituation is affected in autism and related monogenic neurodevelopmental disorders (NDDs). An integrated application of habituation assessment in NDDs and their animal models has unexploited potential for neuroscience and medical care. With the aim to gain mechanistic insights, we systematically retrieved genes that have been demonstrated in the literature to underlie habituation. We identified 258 evolutionarily conserved genes across species, describe the biological processes they converge on, and highlight regulatory pathways and drugs that may alleviate habituation deficits. We also summarize current habituation paradigms and extract the most decisive arguments that support the crucial role of habituation for cognition in health and disease. We conclude that habituation is a conserved, quantitative, cognition- and disease-relevant process that can connect preclinical and clinical work, and hence is a powerful tool to advance research, diagnostics, and treatment of NDDs.

Attenuated alpha oscillation and hyperresponsiveness reveals impaired perceptual learning in migraineurs

Background

Anomalous phantom visual perceptions coupled to an aversion and discomfort to some visual patterns (especially grating in mid-range spatial frequency) have been associated with the hyperresponsiveness in migraine patients. Previous literature has found fluctuations of alpha oscillation (8-14 Hz) over the visual cortex to be associated with the gating of the visual stream. In the current study, we examined whether alpha activity was differentially modulated in migraineurs in anticipation of an upcoming stimulus as well as post-stimulus periods.

Methods

We used EEG to examine the brain activity in a group of 28 migraineurs (17 with aura /11 without) and 29 non-migraineurs and compared their alpha power in the pre/post-stimulus period relative to the onset of stripped gratings.

Results

Overall, we found that migraineurs had significantly less alpha power prior to the onset of the stimulus relative to controls. Moreover, migraineurs had significantly greater post-stimulus alpha suppression (i.e event-related desynchronization) induced by the grating in 3 cycles per degree at the 2nd half of the experiment.

Conclusions

These findings, taken together, provide strong support for the presence of the hyperresponsiveness of the visual cortex of migraine sufferers. We speculate that it could be the consequence of impaired perceptual learning driven by the dysfunction of GABAergic inhibitory mechanism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-022-01410-2.

Dim the Lights: A Narrative Review of Photophobia in Migraine

A preference for darkness is one of the main associated features in people with migraine, the cause remaining a mystery until some decades ago. In this article, we describe the epidemiology of photophobia in migraine and explain the pathophysiological mechanisms following an anatomical structure. In addition, we review the current management of migraine and photophobia. Ongoing characterization of patients with photophobia and its different manifestations continues to increase our understanding of the intricate pathophysiology of migraine and vice versa. Detailed phenotyping of the patient with photophobia is encouraged.

Migraine attacks as a result of hypothalamic loss of control

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Hypothalamo-limbic connectivity reflects the cyclic nature of migraine.

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Hypothalamo-limbic connectivity is largest just before the attack.

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Hypothalamo-limbic connectivity is collapsing during the attack.

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Limbic perfusion is increasing and has a maximum during the attack.

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The disrupted connectivity allows high limbic perfusion, resulting in migraine attack.

Migraine is a complex neurological disorder affecting approximately 12% of the population. The pathophysiology is not yet fully understood, however the clinical features of the disease, such as the cyclic behaviour of attacks and vegetative symptoms, suggest a prominent role of the hypothalamus. Previous research has observed neuronal alterations at different time points during the migraine interval, specifically just before the headache is initiated. We therefore aimed to assess the trajectory of migraineurs’ brain activity over an entire migraine cycle.

Using functional magnetic resonance imaging (fMRI) with pseudo-continuous arterial spin labelling (ASL), we designed a longitudinal intra-individual study to detect the rhythmicity of (1) the cerebral perfusion and (2) the hypothalamic connectivity over an entire migraine cycle. Twelve episodic migraine patients were examined in 82 sessions during spontaneous headache attacks with follow-up recordings towards the next attack.

We detected cyclic changes of brain perfusion in the limbic circuit (insula and nucleus accumbens), with the highest perfusion during the headache attack. In addition, we found an increase of hypothalamic connectivity to the limbic system over the interictal interval towards the attack, then collapsing during the headache phase.

The present data provide strong evidence for the predominant role of the hypothalamus in generating migraine attacks. Due to a genetically-determined cortical hyperexcitability, migraineurs are most likely characterised by an increased susceptibility of limbic neurons to the known migraine trigger. The hypothalamus as a metronome of internal processes is suggested to control these limbic circuits: migraine attacks may occur as a result of the hypothalamus losing control over the limbic system. Repetitive psychosocial stress, one of the leading trigger factors reported by patients, might make the limbic system even more vulnerable and lead to a premature triggering of a migraine attack. Potential therapeutic interventions are therefore suggested to strengthen limbic circuits with dedicated medication or psychological approaches.

The missing N1 or jittered P2: Electrophysiological correlates of pattern glare in the time and frequency domain

Excessive sensitivity to certain visual stimuli (cortical hyperexcitability) is associated with a number of neurological disorders including migraine, epilepsy, multiple sclerosis, autism and possibly dyslexia. Others show disruptive sensitivity to visual stimuli with no other obvious pathology or symptom profile (visual stress) which can extend to discomfort and nausea. We used event‐related potentials (ERPs) to explore the neural correlates of visual stress and headache proneness. We analysed ERPs in response to thick (0.37 cycles per degree [c/deg]), medium (3 c/deg) and thin (12 c/deg) gratings, using mass univariate analysis, considering three factors in the general population: headache proneness, visual stress and discomfort. We found relationships between ERP features and the headache and discomfort factors. Stimulus main effects were driven by the medium stimulus regardless of participant characteristics. Participants with high discomfort ratings had larger P1 components for the initial presentation of medium stimuli, suggesting initial cortical hyperexcitability that is later suppressed. The participants with high headache ratings showed atypical N1‐P2 components for medium stripes relative to the other stimuli. This effect was present only after repeated stimulus presentation. These effects were also explored in the frequency domain, suggesting variations in intertrial theta band phase coherence. Our results suggest that discomfort and headache in response to striped stimuli are related to different neural processes; however, more exploration is needed to determine whether the results translate to a clinical migraine population.

Phonophobia and brainstem excitability in migraine

Phonophobia in migraineurs may be due to lower hearing threshold (HT) and higher brainstem neuronal excitability. We report the correlation of phonophobia in migraineurs with HT, brain stem auditory evoked potential (BAEP) findings, and auditory triggers. Sixty-one migraineurs and 101 controls were included for HT, of whom 59 migraineurs and 31 controls had BAEP studies. Clinical details, migraine triggers, and headache frequency were noted. Hearing threshold was measured, and amplitudes of waves I to V of BAEP studies were measured. Migraineurs had lower HT compared with controls (41.61 ± 5.25 versus 45.39 ± 6.26 dB; p < 0.001) especially in chronic migraine (40.24 ± 4.81; p < 0.001). Hearing threshold correlated with headache frequency (p < 0.05) and auditory, visual, and tactile (p < 0.05) triggers. Hearing threshold was lower during headache (p < 0.001). Wave II, III, and IV amplitudes of BAEP were higher in migraineurs than the controls. Wave II (p < 0.05) and III (p < 0.05) amplitudes correlated with HT. Migraineurs have lower HT, especially in those having chronic migraine, ictal HT recording, and multiple sensory triggers. Higher amplitudes of BAEP waves in migraineurs and their relationship with the frequency of headache and HT suggest the sensitization of brainstem auditory neurons.

Long-Term Effects of Self-Administered Transcranial Direct Current Stimulation in Episodic Migraine Prevention: Results of a Randomized Controlled Trial

BACKGROUND

Migraine is a multifactorial neurovascular disorder, which affects about 12% of the general population. In episodic migraine, the visual cortex revealed abnormal processing, most likely due to decreased preactivation level. Transcranial direct current stimulation (tDCS) is able to modify cortical excitability and might result in an alleviation of migraine occurrence if used repetitively.

OBJECTIVE

To test the hypothesis that self-administered anodal tDCS over the visual cortex significantly decreases the number of monthly migraine days in episodic migraine.

MATERIALS AND METHODS

The study was single-blind, randomized, and sham-controlled. Inclusion criteria were age 18-80 years and an ICHD-3 diagnosis of episodic migraine. Exclusion criteria were pregnancy, presence of a neurodegenerative disorder, a contraindication against MRI examinations, and less than two migraine days during the 28-day baseline period. Patients in whom the baseline period suggested chronic migraine were excluded. After baseline, participants applied daily either verum (anodal-1 mA to 20 min) or sham tDCS (anodal-1 mA to 30 sec) at Oz (reference Cz electrode) for 28 days. Headache diaries were used to record the number of migraine days at baseline, during the stimulation period, and during four subsequent 28-day periods.

RESULTS

Twenty-eight patients were included; two were excluded after the baseline period because less than two migraine days occurred; three were excluded because their headache diaries suggested the diagnosis of chronic migraine. Twenty-three datasets were taken for further analysis. Compared to sham tDCS (n = 12), verum tDCS (n = 11) resulted in a lower number of migraine days (p = 0.010) across all follow-up periods. We found no significant change in total headache days (p = 0.165), anxiety (p = 0.884), or depression scores (p = 0.535). No serious adverse events occurred; minor side effects were similar in both groups.

CONCLUSIONS

This study provides Class II evidence that self-administered anodal tDCS over the visual cortex in episodic migraine results in a significantly lower number of monthly migraine days. However, it has neither an immediate nor a long-term effect.

Migraine as a Cortical Brain Disorder

PURPOSE

Migraine is an exclusively human chronic disorder with ictal manifestations characterized by a multifaceted clinical complexity pointing to a cerebral cortical involvement. The present review is aimed to cover the clinical, neuroimaging, and neurophysiological literature on the role of the cerebral cortex in migraine pathophysiology.

OVERVIEW

Converging clinical scenarios, advanced neuroimaging data, and experimental neurophysiological findings, indicate that fluctuating excitability, plasticity, and metabolism of cortical neurons represent the pathophysiological substrate of the migraine cycle. Abnormal cortical responsivity and sensory processing coupled to a mismatch between the brain's energy reserve and workload may ignite the trigeminovascular system, leading to the migraine attack through the activation of subcortical brain trigeminal and extra-trigeminal structures, and driving its propagation and maintenance.

DISCUSSION

The brain cortex emerges as the crucial player in migraine, a disorder lying at the intersection between neuroscience and daily life. Migraine disorder stems from an imbalance in inhibitory/excitatory cortical circuits, responsible for functional changes in the activity of different cortical brain regions encompassing the neurolimbic-pain network, and secondarily allowing a demodulation of subcortical areas, such as hypothalamus, amygdala, and brainstem nuclei, in a continuous mutual crosstalk.

Auditory attention alterations in migraine: A behavioral and MEG/EEG study

OBJECTIVES

To evaluate alterations of top-down and/or bottom-up attention in migraine and their cortical underpinnings.

METHODS

19 migraineurs between attacks and 19 matched control participants performed a task evaluating jointly top-down and bottom-up attention, using visually-cued target sounds and unexpected task-irrelevant distracting sounds. Behavioral responses and magneto- and electro-encephalography signals were recorded. Event-related potentials and fields were processed and source reconstruction was applied to event-related fields.

RESULTS

At the behavioral level, neither top-down nor bottom-up attentional processes appeared to be altered in migraine. However, migraineurs presented heightened evoked responses following distracting sounds (orienting component of the N1 and Re-Orienting Negativity, RON) and following target sounds (orienting component of the N1), concomitant to an increased recruitment of the right temporo-parietal junction. They also displayed an increased effect of the cue informational value on target processing resulting in the elicitation of a negative difference (Nd).

CONCLUSIONS

Migraineurs appear to display increased bottom-up orienting response to all incoming sounds, and an enhanced recruitment of top-down attention.

SIGNIFICANCE

The interictal state in migraine is characterized by an exacerbation of the orienting response to attended and unattended sounds. These attentional alterations might participate to the peculiar vulnerability of the migraine brain to all incoming stimuli.

The visual system as target of non-invasive brain stimulation for migraine treatment: Current insights and future challenges

The visual network is crucially implicated in the pathophysiology of migraine. Several lines of evidence indicate that migraine is characterized by an altered visual cortex excitability both during and between attacks. Visual symptoms, the most common clinical manifestation of migraine aura, are likely the result of cortical spreading depression originating from the extrastriate area V3A. Photophobia, a clinical hallmark of migraine, is linked to an abnormal sensory processing of the thalamus which is converged with the non-image forming visual pathway. Finally, visual snow is an increasingly recognized persistent visual phenomenon in migraine, possibly caused by increased perception of subthreshold visual stimuli. Emerging research in non-invasive brain stimulation (NIBS) has vastly developed into a diversity of areas with promising potential. One of its clinical applications is the single-pulse transcranial magnetic stimulation (sTMS) applied over the occipital cortex which has been approved for treating migraine with aura, albeit limited evidence. Studies have also investigated other NIBS techniques, such as repetitive TMS (rTMS) and transcranial direct current stimulation (tDCS), for migraine prophylaxis but with conflicting results. As a dynamic brain disorder with widespread pathophysiology, targeting migraine with NIBS is challenging. Furthermore, unlike the motor cortex, evidence suggests that the visual cortex may be less plastic. Controversy exists as to whether the same fundamental principles of NIBS, based mainly on findings in the motor cortex, can be applied to the visual cortex. This review aims to explore existing literature surrounding NIBS studies on the visual system of migraine. We will first provide an overview highlighting the direct implication of the visual network in migraine. Next, we will focus on the rationale behind using NIBS for migraine treatment, including its effects on the visual cortex, and the shortcomings of currently available evidence. Finally, we propose a broader perspective of how novel approaches, the concept of brain networks and the integration of multimodal imaging with computational modeling, can help refine current NIBS methods, with the ultimate goal of optimizing a more individualized treatment for migraine.

Imaging the Visual Network in the Migraine Spectrum

The involvement of the visual network in migraine pathophysiology has been well-known for more than a century. Not only is the aura phenomenon linked to cortical alterations primarily localized in the visual cortex; but also migraine without aura has shown distinct dysfunction of visual processing in several studies in the past. Further, the study of photophobia, a hallmark migraine symptom, has allowed unraveling of distinct connections that link retinal pathways to the trigeminovascular system. Finally, visual snow, a recently recognized neurological disorder characterized by a continuous visual disturbance, is highly comorbid with migraine and possibly shares with it some common pathophysiological mechanisms. Here, we review the most relevant neuroimaging literature to date, considering studies that have either attempted to investigate the visual network or have indirectly shown visual processing dysfunctions in migraine. We do this by taking into account the broader spectrum of migrainous biology, thus analyzing migraine both with and without aura, focusing on light sensitivity as the most relevant visual symptom in migraine, and finally analyzing the visual snow syndrome. We also present possible hypotheses on the underlying pathophysiology of visual snow, for which very little is currently known.

Brain state monitoring for the future prediction of migraine attacks

BACKGROUND

Migraine attacks are unpredictable, precluding preemptive interventions and leading to lack of control over individuals' lives. Although there are neurophysiological changes 24-48 hours before migraine attacks, so far, they have not been used in patients' management. This study evaluates the applicability and the ability to identify pre-attack changes of daily "at home" electroencephalography obtained with a portable system for migraine patients.

METHODS

Patients with episodic migraine fulfilling ICHD-3 beta criteria used a mobile system composed of a wireless EEG device (BrainStation®, Neuroverse®, Inc., USA) and mobile application (BrainVitals_M®, Neuroverse®, Inc., USA) to self-record their neural activity daily at home while resting and while performing an attention task, over the course of 2 weeks. Standard EEG spectral analysis and event-related brain potentials (ERP) methods were used and recordings were grouped by time from migraine attacks (i.e. "Interictal day", "24 h Before Migraine", "Migraine day" and "Post Migraine").

RESULTS

Twenty-four patients (22 women) recorded an average of 13.3 ± 1.9 days and had 2 ± 0.9 attacks. Twenty-four hours before attack onset, there was a statistically significant modulation of relative power in the delta (decrease) and beta (increase) frequency bands, at rest, and a significant reduction of the amplitude and inter-trial coherence measures of an attention event-related brain potential (P300).

CONCLUSIONS

This proof-of-concept study shows that brain state monitoring, utilising an easy-to-use wearable EEG system to track neural modulations at home, can identify physiological changes preceding a migraine attack enabling valuable pre-symptom prediction and subsequent early intervention.

Cathodal Occipital tDCS Is Unable to Modulate the Sound Induced Flash Illusion in Migraine

Migraine is a highly disabling disease characterized by recurrent pain. Despite an intensive effort, mechanisms of migraine pathophysiology still represent an unsolved issue. Evidence from both animal and human studies suggests that migraine is characterized by hyperresponsivity or hyperexcitability of sensory cortices, especially the visual cortex. This phenomenon, in turn, may affect multisensory processing. Indeed, migraineurs present with an abnormal, reduced, perception of the Sound-induced Flash Illusion (SiFI), a crossmodal illusion that relies on optimal integration of visual and auditory stimuli by the occipital visual cortex. Decreasing visual cortical excitability with transcranial direct current stimulation (tDCS) can increase the SiFI in healthy subjects. Moving away from these issues, we applied cathodal tDCS over the visual cortex of migraineurs, with and without aura, in order to decrease cortical excitability and thus physiologically restoring the perception of a reliable SiFI. Differently from our expectations, tDCS was unable to reliably modulate SiFI in migraine. The chronic, relatively excessive, visual cortex hyperexcitability, featuring the migraineur brain, may render tDCS ineffective for restoring multisensory processing in this disease.

Fluctuations of sensorimotor processing in migraine: a controlled longitudinal study of beta event related desynchronization

Background

The migraine brain seems to undergo cyclic fluctuations of sensory processing. For instance, during the preictal phase, migraineurs experience symptoms and signs of altered pain perception as well as other well-known premonitory CNS-symptoms. In the present study we measured EEG-activation to non-painful motor and sensorimotor tasks in the different phases of the migraine cycle by longitudinal measurements of beta event related desynchronization (beta-ERD).

Methods

We recorded electroencephalography (EEG) of 41 migraine patients and 31 healthy controls. Each subject underwent three EEG recordings on three different days with classification of each EEG recording according to the actual migraine phase. During each recording, subjects performed one motor and one sensorimotor task with the flexion-extension movement of the right wrist.

Results

Migraine patients had significantly increased beta-ERD and higher baseline beta power at the contralateral C3 electrode overlying the primary sensorimotor cortex in the preictal phase compared to the interictal phase. We found no significant differences in beta-ERD or baseline beta power between interictal migraineurs and controls.

Conclusion

Increased preictal baseline beta activity may reflect a decrease in pre-activation in the sensorimotor cortex. Altered pre-activation may lead to changes in thresholds for inhibitory responses and increased beta-ERD response, possibly reflecting a generally increased preictal cortical responsivity in migraine. Cyclic fluctuations in the activity of second- and third-order afferent somatosensory neurons, and their associated cortical and/or thalamic interneurons, may accordingly also be a central part of the migraine pathophysiology.

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.

Cerebral hemodynamics in the different phases of migraine and cluster headache

Headache is one of the most common ailments; migraine is one of the most prevalent and disabling neurological disorders and cluster headache presents as one of the most excruciating pain disorders. Both are complex disorder characterized by recurrent episodes of headache. A key feature is that various triggers can set off an attack providing the opportunity to explore disease mechanisms by experimentally inducing attacks. This review summarizes neuroimaging and hemodynamic studies in human in provoked and spontaneous attacks of migraine and cluster headache. Cerebral hemodynamics during different phases of the migraine attack demonstrate alterations in cerebral blood flow and perfusion, vessel caliber, cortical and sub-cortical function, underscoring that migraine pathophysiology is highly complex. Migraine attacks might begin in diencephalic and brainstem areas, whereas migraine aura is a cortical phenomenon. In cluster headache pathophysiology, the hypothalamus might also play a pivotal role, whereas the pattern of cerebral blood flood differs from migraine. For both disorders, alterations of arterial blood vessel diameter might be more an epiphenomenon of the attack than a causative trigger. Studying cerebral hemodynamics in provocation models are important in the search for specific biomarkers in the hope to discover future targets for more specific and effective mechanism-based anti-headache treatment.

Abnormality of visual neuromagnetic activation in female migraineurs without aura between attacks

OBJECTIVE

The present study aimed to preliminary explore the abnormal neuromagnetic activation in female migraine patients between attacks using magnetoencephalography (MEG) and pattern reversed visual evoked magnetic fields (PR-VEFs).

METHODS

A total of 17 female migraine subjects during the headache-free phase and 17 healthy controls (HC) were studied using a 275-channel magnetoencephalography (MEG) system. In this study, visual evoked magnetic fields (VEFs) were generated by a pattern-reversal check as the visual stimulus. The average of 100 VEFs was evolved by different half patterns were averaged and used to analyze waveform, spectrum, and source location within two frequency ranges (5-100 and 100-1000 Hz), respectively.

RESULTS

In migraine subjects, the latency of second peak of VEFs (VIIs) showed significant prolongations when compared with HC. On the sensor level, the cortical spectral power in migraine subjects was similar to that of HC in the 5-100 Hz range and was lower in the 1000-1000 Hz range. There was a decrement of source strength in the visual cortex in migraine patients when compared to HC in both the 5-100 and 100-1000 Hz frequency range. Moreover, there was a similar odds of activation in 5-100 and 100-1000 Hz frequency ranges in the area beyond the primary visual cortex between the two groups. In addition, no correlation was observed between clinical data (intensity of headache, headache-history duration, the frequency of headaches) and MEG results.

CONCLUSIONS

The findings presented in the current study, suggested that interictal cortical activation following a visual stimulus was low in female migraine patients. The low pre-activation was detected in the visual cortex using VEF and MEG in both low and high-frequency band. Our results add to the existing evidence that cortical interictal excitability change may be relative to the pain-module mechanism in migraine brains. Thus, our data improved the apprehension of the cortical disorder of migraine in the high-frequency domain.

Temporal Modulation of Steady-State Visual Evoked Potentials

Electroencephalographic responses to periodic stimulation are termed steady-state visual evoked potentials (SSVEP). Their characteristics in terms of amplitude, frequency and phase are commonly assumed to be stationary. In this work, we tested this assumption in 30 healthy participants submitted to 50 trials of 60 s flicker stimulation at 15 Hz frequency. We showed that the amplitude of the first and second harmonic frequency components of SSVEP signals were in general not stable over time. The power (squared amplitude) of the fundamental component was stationary only in 30% the subjects, while the power at the second harmonic frequency was stationary in 66.7% of the group. The phases of both SSVEP frequency components were more stable over time, but could exhibit small drifts. The observed temporal changes were heterogeneous across the subjects, implying that averaging results over participants should be performed carefully. These results may contribute to improved design and analysis of experiments employing prolonged visual stimulation. Our findings offer a novel characterization of the temporal changes of SSVEP that may help to identify their physiological basis.

Postural instability during attacks of migraine without aura

BACKGROUND AND PURPOSE

Migraine has long been associated with unsteadiness and dizziness but postural control has not been studied in the ictal state. Here, the stability of upright stance during migraine attacks was measured.

METHODS

Static balance was assessed prospectively in migraine patients (n = 30) during quiet stance for 40 s on a posturographic force platform. Recordings were performed both ictally and in the pain-free interval. Subjects were assessed under four different conditions yielding different visual and proprioceptive feedback environments. Both ictal and interictal data were compared with age-matched healthy controls (n = 30).

RESULTS

Postural instability increased significantly under all experimental conditions during migraine attacks. Whilst standing on a foam pad with eyes closed, median sway area was 353 mm² in control subjects, 318 mm² in migraineurs in the pain-free period and 618 mm² in the ictal state. However, Romberg and vestibular Romberg quotients were not altered during migraine attacks. Spectral analyses of postural sway also showed similar profiles in migraineurs and controls. The severity of headache was inversely correlated to Romberg quotients.

CONCLUSIONS

The demonstrated pattern of balance disorder during migraine attacks suggests a transient cerebellar dysfunction. Our findings also indicate that intense headache induces a re-weighting of sensory processing toward less dependence on visual and proprioceptive information.

Migraine and cluster headache - the common link

Although clinically distinguishable, migraine and cluster headache share prominent features such as unilateral pain, common pharmacological triggers such glyceryl trinitrate, histamine, calcitonin gene-related peptide (CGRP) and response to triptans and neuromodulation. Recent data also suggest efficacy of anti CGRP monoclonal antibodies in both migraine and cluster headache. While exact mechanisms behind both disorders remain to be fully understood, the trigeminovascular system represents one possible common pathophysiological pathway and network of both disorders. Here, we review past and current literature shedding light on similarities and differences in phenotype, heritability, pathophysiology, imaging findings and treatment options of migraine and cluster headache. A continued focus on their shared pathophysiological pathways may be important in paving future treatment avenues that could benefit both migraine and cluster headache patients.

Neuronal Dysexcitability May Be a Biomarker of Migraine: A Visual Evoked Potential Study

We report neuronal sensitization and impaired habituation in migraine using pattern reversal visual evoked potential (PRVEP) and correlate these with clinical characteristics of migraine. Sixty-five migraineurs and 30 healthy controls were included. A detailed clinical examination was done and migraine characteristics, including migraine trigger, photophobia, phonophobia, and allodynia were noted. Consecutive 5 blocks of PRVEP were recorded averaging 100 epochs at 3 Hz stimuli. The amplitude of N75 and P100 were measured. Amplitude of first block was considered for sensitization, and impaired habituation was considered if any subsequent block was not suppressed. Migraineurs had sensitization of P100 (14.01 ± 6.02 vs 11.60 ± 5.17 µV; P = .049), but not of N75 (42.22 ± 4.79 vs 11.08 ± 4.56 µV; P = .27) compared with the controls. Impaired habituation of N75 was more marked and persisted up to fourth block of VEP recoding. Impaired habituation of P100 was significant only in the third block. Baseline N75 and P100 amplitudes were higher in females, and N75 was also higher in those with longer duration of illness. These phenomena did not correlate with visual triggers. Sensitization and impaired habituation were marked during headache. Based on the PRVEP findings, it may be concluded that migraineurs have sensitization of P100 and impaired habituation of N75 especially during headache. These phenomena may be useful for therapeutic monitoring.

Temporal Integration of Motion Streaks in Migraine

Migraine is associated with differences in visual perception, specifically, deficits in the perception of motion. Migraine groups commonly show poorer performance (higher thresholds) on global motion tasks compared to control groups. Successful performance on a global motion task depends on several factors, including integrating signals over time. A "motion streak" task was used to investigate specifically integration over time in migraine and control groups. The motion streak effect depends on the integration of a moving point over time to create the illusion of a line, or "streak". There was evidence of a slower optimum speed for eliciting the motion streak effect in migraine compared to control groups, suggesting temporal integration is different in migraine. In addition, performance on the motion streak task showed a relationship with headache frequency.

Electrophysiological Characteristics of the Migraine Brain: Current Knowledge and Perspectives

BACKGROUND

Despite pain being its most prominent feature, migraine is primarily a disorder of sensory processing. Electrophysiology-based research in the field has consistently developed over the last fifty years.

OBJECTIVE

To summarize the current knowledge on the electrophysiological characteristics of the migraine brain, and discuss perspectives.

METHODS

We critically reviewed the literature on the topic to present and discuss articles selected on the basis of their significance and/or novelty.

RESULTS

Physiologic fluctuations within time, between-subject differences, and methodological issues account as major limitations of electrophysiological research in migraine. Nonetheless, several abnormalities revealed through different approaches have been described in the literature. Altogether, these results are compatible with an abnormal state of sensory processing.

PERSPECTIVES

The greatest contribution of electrophysiological testing in the future will most probably be the characterization of sub-groups of migraine patients sharing specific electrophysiological traits. This should serve as strategy towards personalized migraine treatment. Incorporation of novel methods of analysis would be worthwhile.

Neural Habituation to Painful Stimuli Is Modulated by Dopamine: Evidence from a Pharmacological fMRI Study

In constantly changing environments, it is crucial to adaptively respond to threatening events. In particular, painful stimuli are not only processed in terms of their absolute intensity, but also with respect to their context. While contextual pain processing can simply entail the repeated processing of information (i.e., habituation), it can, in a more complex form, be expressed through predictions of magnitude before the delivery of nociceptive information (i.e., adaptive coding). Here, we investigated the brain regions involved in the adaptation to nociceptive electrical stimulation as well as their link to dopaminergic neurotransmission (placebo/haloperidol). The main finding is that haloperidol changed the habituation to the absolute pain intensity over time. More precisely, in the placebo condition, activity in left postcentral gyrus and midcingulate cortex increased linearly with pain intensity only in the beginning of the experiment and subsequently habituated. In contrast, when the dopaminergic system was blocked by haloperidol, a linear increase with pain intensity was present throughout the entire experiment. Finally, there were no adaptive coding effects in any brain regions. Together, our findings provide novel insights into the nature of pain processing by suggesting that dopaminergic neurotransmission plays a specific role for the habituation to painful stimuli over time.

Sunlight irradiance and habituation of visual evoked potentials in migraine: The environment makes its mark

Background Migraine is a complex multifactorial disease that arises from the interaction between a genetic predisposition and an enabling environment. Habituation is considered as a fundamental adaptive behaviour of the nervous system that is often impaired in migraine populations. Given that migraineurs are hypersensitive to light, and that light deprivation is able to induce functional changes in the visual cortex recognizable through visual evoked potentials habituation testing, we hypothesized that regional sunlight irradiance levels could influence the results of visual evoked potentials habituation studies performed in different locations worldwide. Methods We searched the literature for visual evoked potentials habituation studies comparing healthy volunteers and episodic migraine patients and correlated their results with levels of local solar radiation. Results After reviewing the literature, 26 studies involving 1291 participants matched our inclusion criteria. Deficient visual evoked potentials habituation in episodic migraine patients was reported in 19 studies. Mean yearly sunlight irradiance was significantly higher in locations of studies reporting deficient habituation. Correlation analyses suggested that visual evoked potentials habituation decreases with increasing sunlight irradiance in migraine without aura patients. Conclusion Results from this hypothesis generating analysis suggest that variations in sunlight irradiance may induce adaptive modifications in visual processing systems that could be reflected in visual evoked potentials habituation, and thus partially account for the difference in results between studies performed in geographically distant centers. Other causal factors such as genetic differences could also play a role, and therefore well-designed prospective trials are warranted.

Initiation of spreading depression by synaptic and network hyperactivity: Insights into trigger mechanisms of migraine aura

Background

Cortical spreading depression (SD) is thought to underlie migraine aura but mechanisms of triggering SD in the structurally normal, well-nourished cortex of migraine patients remain unknown. Synaptic and network dysfunctions appear to underlie episodic neurological disorders, including migraine. The narrative review summarizes old and recent experimental evidence for triggering SD by synaptic/network mechanisms and discusses the relevance of the data to migraine pathogenesis. Our hypothesis is that under some conditions synaptic/network hyperactivity may reliably ignite SD, and this mechanism may underlie triggering migraine aura in patients.

Findings

High-frequency tetanic stimulation of the cortex reliably triggers SD in synaptically connected regions; SD is a reliable cortical response to acute hyperexcitability (epileptic seizures), though chronic epilepsy prevents triggering SD; in the hyperexcitable cortex, SD may be triggered by sensory stimulation; compromised glutamatergic transmission plays the critical role in triggering SD.

Conclusion

SD may be triggered by dynamic network instability produced by dysfunction of calcium-dependent glutamate release. Synaptic drive from subcortical sensory processing structures (brainstem and/or thalamocortical networks) is able to evoke depolarization of hyperexcitable cortical neurons sufficient to initiate the regenerative SD process. Studying SD initiation by synaptic/network hyperexcitability may provide insights into basic mechanisms underlying SD generation in migraine brain.

Effect of inter-train interval on the induction of repetition suppression of motor-evoked potentials using transcranial magnetic stimulation

Repetition suppression (RS) is evident as a weakened response to repeated stimuli after the initial response. RS has been demonstrated in motor-evoked potentials (MEPs) induced with transcranial magnetic stimulation (TMS). Here, we investigated the effect of inter-train interval (ITI) on the induction of RS of MEPs with the attempt to optimize the investigative protocols. Trains of TMS pulses, targeted to the primary motor cortex by neuronavigation, were applied at a stimulation intensity of 120% of the resting motor threshold. The stimulus trains included either four or twenty pulses with an inter-stimulus interval (ISI) of 1 s. The ITI was here defined as the interval between the last pulse in a train and the first pulse in the next train; the ITIs used here were 1, 3, 4, 6, 7, 12, and 17 s. RS was observed with all ITIs except with the ITI of 1 s, in which the ITI was equal to ISI. RS was more pronounced with longer ITIs. Shorter ITIs may not allow sufficient time for a return to baseline. RS may reflect a startle-like response to the first pulse of a train followed by habituation. Longer ITIs may allow more recovery time and in turn demonstrate greater RS. Our results indicate that RS can be studied with confidence at relatively short ITIs of 6 s and above.

Preventive drugs restore visual evoked habituation and attention in migraineurs

Visual system pathway dysfunction has been postulated in migraineurs. We wanted to investigate if any difference exists interictally in visual attention and visual evoked habituation of frequently attacked migraineurs compared to the healthy control group. The effects of 3-month prophylactic migraine treatment on these parameters were also assessed. The migraineurs at headache-free interval (n = 52) and age, sex-matched healthy controls (n = 35) were compared by habituation response to 10 blocks of repetitive pattern-reversal visual stimuli (each block consisted 100 responses). The amplitude changes of 5th and 10th blocks were further compared with that of block 1 to assess the response of habituation (i.e., decrease) or potentiation (i.e., increase). The level of sustained visual attention was assessed by Cancellation test. Migraineurs were randomized to three different preventive treatments: propranolol 40 mg tid, flunarizine 5 mg bid, or topiramate 50 mg bid. After 3 months of preventive treatment, migraineurs data were compared with their baseline values. The groups did not differ by sex and age. In electrophysiological studies, the habituation ability observed in the healthy group was not observed in migraineurs. However, it was restored 3 months after preventive treatment. In migraineurs, compared to their baseline values, the distorted visual attention parameters also improved after treatment. All drugs were effective. The loss of habituation ability and low visual attention performance in migraineurs can be restored by migraine preventive treatment. This electrophysiological study accompanied by neuropsychological test may aid an objective and quantitative assessment tool for understanding migraine pathophysiology.

Effect of high rate rTMS on somatosensory evoked potential in migraine

Background

Sensitization and impaired habituation of cortical neurons have been reported in migraineurs. Repetitive transcranial magnetic stimulation (rTMS) may change these phenomena and be the basis of therapeutic response. We report the effect of 10 Hz rTMS on sensitization and habituation of median somatosensory evoked potential (SEP) in migraineurs, and correlate these changes with clinical response.

Methods

Migraineurs having four or more episodes of headache per month were included and their clinical details were noted. Three sessions of 10 Hz rTMS, 600 pulses in 412.4 seconds were delivered on the left frontal cortex corresponding to the hot spot of right abductor digiti minimi, on alternate days. Median SEP was done before and 30 minutes after the third rTMS session. Sensitization (block I N20 amplitude) and impaired habituation (if N20 amplitude of block 2 or 3 were not suppressed compared to block I) were noted. The reduction in frequency and severity of headache in the next month were noted and correlated with SEP changes.

Results

Ninety-four migraineurs were included; 56 received true rTMS and 38 sham stimulation. Following stimulation, reduction in N20 amplitude of block 1 correlated with a reduction in frequency and severity of headache at one month. The impaired habituation significantly improved in the true rTMS group compared to sham stimulation, and correlated with a reduction in the severity of headache but not with frequency.

Conclusion

In migraineurs, 10 Hz rTMS improves habituation and may be the biological basis of headache relief.

Visual and auditory cortical evoked potentials in interictal episodic migraine: An audit on 624 patients from three centres

Background

Many studies report a habituation deficit of visual evoked potentials (VEP) and/or increased intensity dependence of auditory evoked cortical potentials (IDAP) in episodic migraine patients between attacks. These findings have a pathophysiological interest, but their diagnostic utility is not known.

Aims

To perform an audit on a large database of interictal VEP and IDAP recordings in episodic migraine patients and evaluate their diagnostic accuracy.

Methods

We pooled data for VEP habituation and IDAP measured in 624 episodic migraineurs (EM) and 360 healthy volunteers (HV) from three centers. Thresholds were calculated by Receiver Operating Curve analysis and used to calculate sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-) and the accuracy of each test, using ICHD diagnostic criteria as the gold standard.

Results

In EM, VEP habituation was significantly lower than in HV, and IDAP slopes were significantly steeper. VEP (five blocks of 50 responses), VEP (six blocks of 100 responses) and IDAP had respectively 61.0%, 61.4% and 45.7% sensitivity, and 77.9%, 77.9% and 87.2% specificity. Their positive (LR+) and negative (LR-) likelihood ratios were respectively 2.760, 2.778, 3.570 and 0.500, 0.495, 0.623, with diagnostic accuracies of 65.3%, 69.0% and 54.3%. In combined VEP + IDAP recordings, an abnormality of at least one test had 83.4% sensitivity, 66.7% specificity, 2.504 LR+, 0.249 LR− and 81.1% accuracy.

Conclusions

In this large database, VEP habituation is significantly reduced and IDAP increased in episodic migraine patients between attacks. Taken alone, neither VEP nor IDAP has sufficient diagnostic accuracy. However, when both tests are performed in the same patient, an abnormality of at least one of them is highly predictive of interictal episodic migraine.

Visual processing in migraine

Background

Migraine is a common neurological condition that often involves differences in visual processing. These sensory processing differences provide important information about the underlying causes of the condition, and for the development of treatments.

Review of psychophysical literature

Psychophysical experiments have shown consistent impairments in contrast sensitivity, orientation acuity, and the perception of global form and motion. They have also established that the addition of task-irrelevant visual noise has a greater effect, and that surround suppression, masking and adaptation are all stronger in migraine.

Theoretical signal processing model

We propose utilising an established model of visual processing, based on signal processing theory, to account for the behavioural differences seen in migraine. This has the advantage of precision and clarity, and generating clear, falsifiable predictions.

Conclusion

Increased effects of noise and differences in excitation and inhibition can account for the differences in migraine visual perception. Consolidating existing research and creating a unified, defined theoretical account is needed to better understand the disorder.

Interictal Lack of Habituation of Mismatch Negativity in Migraine

The aim was to study mismatch negativity features and habituation during the interictal phase of migraine. In migraine patients, a strong negative correlation has been found between the initial amplitude of long latency auditory-evoked potentials and their amplitude increase during subsequent averaging. We studied 12 outpatients with a diagnosis of migraine without aura recorded in a headache-free interval and 10 gender- and age-matched healthy volunteers not suffering from any recurrent headache. The experiment consisted of two sequential blocks of 2000 stimulations, during which 1800 (90%) recordings for standard tones and 200 (10%) for target tones were selected for averaging. The latency of the N1 component was significantly increased in migraine patients in respect of controls in both the first and second repetitions; the MMN latency was increased in the second repetition. In the control group the MMN amplitude decreased on average by 3.2 ± 1.4 μV in the second trial, whereas in migraine patients it showed a slight increase of 0.21 ± 0.11 μV in the second repetition. The MMN latency relieved in the second trial was significantly correlated with the duration of illness in the migraine patients (Spearman correlation coefficient: 0.69; P < 0.05). The increases in N1 latency and MMN latency and amplitude, the latter correlated with duration of illness, seemed to be due to a reduced anticipatory effect of stimulus repetition in migraine patients. This suggests that such hypo-activity of automatic cortical processes, subtending the discrimination of acoustic stimuli, may be a basic abnormality in migraine, developing in the course of the disease.

Interictal Abnormalities of Gamma Band Activity in Visual Evoked Responses in Migraine: An Indication of Thalamocortical Dysrhythmia?

Between attacks, migraineurs lack habituation in standard visual evoked potentials (VEPs). Visual stimuli also evoke high-frequency oscillations in the gamma band range (GBOs, 20–35 Hz) assumed to be generated both at subcortical (early GBOs) and cortical levels (late GBOs). The consecutive peaks of GBOs were analysed regarding amplitude and habituation in six successive blocks of 100 averaged pattern reversal (PR)-VEPs in healthy volunteers and interictally in migraine with (MA) or without aura patients. Amplitude of the two early GBO components in the first PR-VEP block was significantly increased in MA patients. There was a significant habituation deficit of the late GBO peaks in migraineurs. The increased amplitude of early GBOs could be related to the increased interictal visual discomfort reported by patients. We hypothesize that the hypo-functioning serotonergic pathways may cause, in line with the thalamocortical dysrhythmia theory, a functional disconnection of the thalamus leading to decreased intracortical lateral inhibition, which can induce dishabituation.