Pattern reversal visual evoked potentials in classic and common migraine

Does levetiracetam use affect visual evoked potentials in the treatment of childhood epilepsy?

BACKGROUND

Side effects of antiepileptic drugs vary depending on the drug itself, drug dose and duration of use. One of these side effects is related to vision.

METHODS

Patients who had been ordered visual evoked potential (VEP) measurements for various reasons between October 1st, 2017 and October 1st, 2019 at a pediatric neurology outpatient clinic and who were on levetiracetam monotherapy for at least six months for the treatment of focal/generalized epilepsy were included in the study and their files were scanned retrospectively (study group: SG). Patient files were evaluated for age, gender, dose and duration of levetiracetam use, presence of a family history of epilepsy, EEG result, cranial magnetic resonance imaging and VEP test results and the parameters were recorded. Twenty-four patients of similar age range without epilepsy were included in the study as the control group (CG).

RESULTS

Eighteen patients 8 boys (44.4%), 10 girls (55.6%) and 24 healthy controls 9 boys (37.5%), 15 girls (62.5%) were included in the study and control groups, respectively. No statistically significant difference was found when the mean VEP latencies were compared between the patient and control groups for the right (P=0.451) and left (P=0.323) eyes. There was a statistically significant difference between the groups, respectively, when VEP amplitudes of the right and left eyes of the SG and CG were compared (P=0.001; P=0.001). There is no correlation between levetiracetam dose and duration of treatment and VEP parameters.

CONCLUSIONS

The data obtained in this study showed that levetiracetam use affected VEP amplitude outcome but did not affect VEP latency outcome in pediatric patients.

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.

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.

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.

P3 latency as a biomarker for the complexity of migraine with aura: Event-related potential study

BACKGROUND

This study aimed to compare the P3 component between patients who have migraines with aura and healthy subjects, and to compare different subtypes of migraine with aura relative to the complexity of migraine aura.

METHODS

Average Migraine Aura Complexity Score was calculated for each MwA patient. Visual oddball paradigm was used to elicit the P3 component. P3 amplitudes and latencies elicited from frequent and rare stimuli, as well as from difference wave, were compared with healthy subjects. Subsequently, subtypes of migraine with aura were compared and Average Migraine Aura Complexity Score was used to explore the connection between features of the P3 and complexity of migraine with aura.

RESULTS

37 patients who have migraine with aura (16 with simple aura and 21 with complex aura) patients and 28 healthy subjects were studied. Patients who have migraine with aura had significantly prolonged latencies compared to healthy subjects (411 ± 39 ms vs 372 ± 34 ms, p < 0.001) relative to a rare condition. Patients who have complex aura significantly differs from patients who have simple aura (427 ± 34 ms vs 389 ± 35 ms, p = 0.004) and healthy subjects (372 ± 34 ms, p < 0.001) relative to P3 latency in a rare condition and the patients who have complex aura significantly differs from healthy subjects (442 ± 37 ms vs 394 ± 33 ms, p < 0.001) relative to P3 latency in difference wave. P3 latency from rare condition positively correlated with the Average Migraine Aura Complexity Score (p < 0.001).

CONCLUSIONS

Visual oddball paradigm, particularly rare stimuli, could serve as a potential new tool for deep profiling of different clinical complexities among patients who have migraine with aura. Also, the present pattern of P3 components provided new evidence for the cognitive dysfunctions in patients who have migraine with aura.

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

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

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

BACKGROUND

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

MAIN BODY

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

Differences in early and late pattern-onset visual-evoked potentials between self- reported migraineurs and controls

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Migraineurs had an enhanced N2 evoked by gratings with a spatial frequency of 13 cpd.

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Migraineurs had an attenuated occipital late negativity (LN) for viewing all gratings.

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Hyperexcitable controls showed similar VEP pattern compared to migraineurs.

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Enhanced N2 deflection could be driven by cortical hyperexcitation.

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LN reduction could reflect inhibitory control during processing of aversive stimuli.

Striped patterns have been shown to induce strong visual illusions and discomforts to migraineurs in previous literature. Previous research has suggested that these unusual visual symptoms to be linked with the hyperactivity on the visual cortex of migraine sufferers. The present study searched for evidence supporting this hypothesis by comparing the visual evoked potentials (VEPs) elicited by striped patterns of specific spatial frequencies (0.5, 3, and 13 cycles-per-degree) between a group of 29 migraineurs (17 with aura/12 without) and 31 non-migraineurs. In addition, VEPs to the same stripped patterns were compared between non-migraineurs who were classified as hyperexcitable versus non-hyperexcitable using a previously established behavioural pattern glare task. We found that the migraineurs had a significantly increased N2 amplitude for stimuli with 13 cpd gratings but an attenuated late negativity (LN: 400 – 500 ms after the stimuli onset) for all the spatial frequencies. Interestingly, non-migraineurs who scored as hyperexcitable appeared to have similar response patterns to the migraineurs, albeit in an attenuated form. We propose that the enhanced N2 could reflect disruption of the balance between parvocellular and magnocellular pathway, which is in support of the cortical hyperexcitation hypothesis in migraineurs. In addition, the attenuation of the late negativity could reflect a top-down feedback mechanism to suppress visual processing of an aversive stimulus.

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.

Brain Correlates of Single Trial Visual Evoked Potentials in Migraine: More Than Meets the Eye

Background: Using conventional visual evoked potentials (VEPs), migraine patients were found to be hyperresponsive to visual stimulus. Considering that a significant portion of neuronal activity is lost for analysis in the averaging process of conventional VEPs, in this study we investigated visual evoked responses of migraine patients and healthy volunteers using a different approach: single trial analysis. This method permits to preserve all stimulus-induced neuronal activations, whether they are synchronized or not. In addition, we used MRI voxel-based morphometry to search for cortical regions where gray matter volume correlated with single trial (st) VEP amplitude. Finally, using resting-state functional MRI, we explored the connectivity between these regions. Results: stVEP amplitude was greater in episodic migraine patients than in healthy volunteers. Moreover, in migraine patients it correlated positively with gray matter volume of several brain areas likely involved in visual processing, mostly belonging to the ventral attention network. Finally, resting state functional connectivity corroborated the existence of functional interactions between these areas and helped delineating their directions. Conclusions: st-VEPs appear to be a reliable measure of cerebral responsiveness to visual stimuli. Mean st-VEP amplitude is higher in episodic migraine patients compared to controls. Visual hyper-responsiveness in migraine involves several functionally-interconnected brain regions, suggesting that it is the result of a complex multi-regional process coupled to stimulus driven attention systems rather than a localized alteration.

Rating of Olfactory Judgements in Migraine Patients

The aim of this study was to evaluate olfactory hypersensitivity (OHS) between attacks in migraine patients. Seventy-four migraine patients and 30 controls were enrolled. The presence of OHS was evaluated using an oral questionnaire and a chemical odour intolerance index. Subjects had to rate the intensity and hedonicity of 12 odourants using a linear rating scale. Twenty-six patients (35.2±) but no control subjects reported an interictal OHS ( P < 0.001). Logistic regression analysis showed that patients with OHS presented a greater attack frequency, a higher number of odour-induced migraines and visual hypersensitivity when compared with other patients. Disease duration, age, gender and auditory hypersensitivity were not associated with OHS. OHS patients judged odours less pleasant than did other patients and controls, whereas the intensity scores were identical in both groups. OHS between attacks was significantly associated with odour-triggered migraine and an alteration of hedonic judgement.

Auditory Event-Related Potentials and Reaction Times in Migraine Children

Cognitive processing was investigated interictally in 18 children with migraine without aura and 18 age-matched controls by measuring event-related potentials (ERPs) and reaction times (RTs) during an acoustic oddball paradigm. Results showed that N100 amplitude evoked by frequent stimuli was significantly smaller in patients compared with controls. Habituation of target P300 amplitude was observed in patients but not in controls. Mean RTs were equivalent in the two groups, but migraine children made more errors than controls.

Pattern-Reversal Visual Evoked Potential Parameters and Migraine in the Teenage Population

Although migraine represents one of the most common form of primary headache in the teenage population, most neurophysiologic studies are only on the adulthood. We investigated 38 teenage patients with migraine with aura, 17 male and 21 female, with a mean age of 16.2 years, comparing them with gender- and age-matched patients with migraine without aura and healthy subjects. Also, characteristics of aura were correlated with pattern-reversal visual evoked potential parameters. There was a significant difference in left and right eye N2 wave latencies between migraine with aura and migraine without aura patients or healthy controls. In migraine with aura and migraine without aura, 26.3% of patients had abnormal wave latency. Reported tunnel vision during the aura was correlated with lower N1P1 and/or P1N2 wave amplitudes. Also, higher amplitude in patients with migraine with aura correlated with younger age and earlier disease onset, whereas longer aura duration correlated with prolonged wave latency. Findings suggest that migraine subtypes may be differentiated on the basis of N2 wave latency prolongation.

Olfactory processing in adults with autism spectrum disorders

Background

As evidenced in the DSM-V, autism spectrum disorders (ASD) are often characterized by atypical sensory behavior (hyper- or hypo-reactivity), but very few studies have evaluated olfactory abilities in individuals with ASD.

Methods

Fifteen adults with ASD and 15 typically developing participants underwent olfactory tests focused on superficial (suprathreshold detection task), perceptual (intensity and pleasantness judgment tasks), and semantic (identification task) odor processing.

Results

In terms of suprathreshold detection performance, decreased discrimination scores and increased bias scores were observed in the ASD group. Furthermore, the participants with ASD exhibited increased intensity judgment scores and impaired scores for pleasantness judgments of unpleasant odorants. Decreased identification performance was also observed in the participants with ASD compared with the typically developing participants. This decrease was partly attributed to a higher number of near misses (a category close to veridical labels) among the participants with ASD than was observed among the typically developing participants.

Conclusions

The changes in discrimination and bias scores were the result of a high number of false alarms among the participants with ASD, which suggests the adoption of a liberal attitude in their responses. Atypical intensity and pleasantness ratings were associated with hyperresponsiveness and flattened emotional reactions, respectively, which are typical of participants with ASD. The high number of near misses as non-veridical labels suggested that categorical processing is functional in individuals with ASD and could be explained by attention-deficit/hyperactivity disorder. These findings are discussed in terms of dysfunction of the olfactory system.

Visual evoked potentials in subgroups of migraine with aura patients

Background

Patients suffering from migraine with aura can have either pure visual auras or complex auras with sensory disturbances and dysphasia, or both. Few studies have searched for possible pathophysiological differences between these two subgroups of patients.

Methods

Methods - Forty-seven migraine with aura patients were subdivided in a subgroup with exclusively visual auras (MA, N = 27) and another with complex neurological auras (MA+, N = 20). We recorded pattern-reversal visual evoked potentials (VEP: 15 min of arc cheques, 3.1 reversal per second, 600 sweeps) and measured amplitude and habituation (slope of the linear regression line of amplitude changes from the 1st to 6th block of 100 sweeps) for the N1-P1 and P1-N2 components in patients and, for comparison, in 30 healthy volunteers (HV) of similar age and gender distribution.

Results

VEP N1-P1 habituation, i.e. amplitude decrement between 1st and 6th block, which was obvious in most HV (mean slope −0.50), was deficient in both MA (slope +0.01, p = 0.0001) and MA+ (−0.0049, p = 0.001) patients. However, VEP N1-P1 amplitudes across blocks were normal in MA patients, while they were significantly greater in MA+ patients than in HVs.

Conclusions

Our findings suggest that in migraine with aura patients different aura phenotypes may be underpinned by different pathophysiological mechanisms. Pre-activation cortical excitability could be higher in patients with complex neurological auras than in those having pure visual auras or in healthy volunteers.

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.

Sequential changes in neuronal activity in single neocortical neurons after spreading depression

BACKGROUND

Cortical spreading depression (CSD) has an important role in migraine with aura. Prolonged neuronal depression is followed by a late excitatory synaptic plasticity after CSD.

METHOD

Intra- and extracellular recordings were performed to investigate the effect of CSD on intracellular properties of mouse neocortical tissues in the late excitatory period.

RESULTS

During CSD, changes in the membrane potentials usually began with a relatively short hyperpolarization followed by an abrupt depolarization. These changes occurred roughly at the same time point after CSD as the beginning of the negative extracellular deflection. Forty-five minutes after CSD, neurons showed significantly smaller amplitude of afterhyperpolarization and a reduced input resistance. Depolarization and hyperpolarization of the cells by constant intracellular current injections in this period significantly changed the frequency of the action potentials.

CONCLUSION

These data indicate higher excitability of the neocortical neurons after CSD, which can be assumed to contribute to hyperexcitability of neocortical tissues in patients suffering from migraine.

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.

Who is at risk for ongoing dizziness and psychological strain after a vestibular disorder?

Patients with vestibular vertigo syndromes often suffer from anxiety and depression, whereas patients with psychiatric disorders often experience subjective unsteadiness, dizziness, or vertigo. Thus, it has been hypothesized that the vestibular system may be interlinked with the emotion processing systems. The aim of the current study was to evaluate this hypothesis by correlating vestibular and psychiatric symptoms with the course of the disease over 1 year. This interdisciplinary, prospective, longitudinal study included a total of 68 patients with acute vestibular vertigo syndromes. Four subgroups of patients with benign paroxysmal positioning vertigo (BPPV, n=19), acute vestibular neuritis (VN, n=14), vestibular migraine (VM, n=27), or Menière's disease (MD, n=8) were compared. All patients underwent neurological and neuro-otological examinations and filled out standardized self-report inventories including the Vertigo Symptom Scale (VSS), the Vertigo Handicap Questionnaire (VHQ) and the Symptom Checklist 90R (GSI, SCL-90R) at five different times (T0-T4) in the course of 1 year. VM patients experienced significantly more "vertigo and related symptoms" (VSS-VER), "somatic anxiety and autonomic arousal" (VSS-AA), and "vertigo induced handicap" (VHQ) than all other patients (P<0.001-P=0.006). Patients with a positive history of psychiatric disorders had significantly more emotional distress (GSI, SCL-90R), regardless of the specific phenomenology of the four diagnostic subgroups. Finally, fluctuations of vestibular excitability correlated positively with the extent of subjectively perceived vertigo. VM patients are significantly more handicapped by vertigo and related symptoms. They show significantly elevated fluctuations of vestibular excitability, which correlate with the (subjective) severity of vertigo symptoms.

Visual paired-pulse stimulation reveals enhanced visual cortex excitability in migraineurs

Migraine is a common ictal disorder with an interindividual heterogeneous characteristic, whose underlying mechanisms remain elusive. On the one hand migraine is associated with abnormal cortical hyperexcitability. On the other hand, studies reported lower amplitudes of visual-evoked potentials (VEPs) and concluded that low preactivation levels imply decreased excitability. Here we measured visual cortex excitability and paired-pulse suppression in subjects suffering from migraine without aura and in a group of aged- and gender-matched healthy subjects to address the relation between activation levels and excitability. To that aim, we analysed amplitudes of VEPs and paired-pulse suppression evoked by a paired-pulse stimulation paradigm using stimulus onset asynchronies (SOAs) between 80 and 133 ms. We found that in migraineurs in the interictal state the amplitudes of the first VEP were reduced as compared with healthy subjects by approximately 20%. In the case of paired-pulse suppression comparable to healthy controls, the second response amplitude should be reduced as well, which was not the case. Instead, the ratio between the first and second VEP was higher than in healthy controls and did not depend on SOA in the range tested, which demonstrates reduced paired-pulse suppression and therefore implicates increased cortical excitability. Our data show that in migraineurs VEPs were reduced presumably due to reduced activation levels. However, paired-pulse suppression using short SOAs in the range of 100 ms or less was even higher than in normal subjects. Thus, our data show that signatures of both hyper- and hypoexcitability can be found depending on stimulation condition.

Early signs of visual perception and evoked potentials in radiologically asymptomatic boys with X-linked adrenoleukodystrophy

The aim was to identify the electrophysiological and psychological signs at a very early stage in asymptomatic boys with childhood cerebral X-linked adrenoleukodystrophy. Flash visual evoked potentials, pattern reversal, and visual event-related potentials were recorded in 6 radiologically asymptomatic boys with adrenoleukodystrophy and 22 control boys. The latency and amplitude of P100 of visual evoked potentials and P1 of event-related potentials were evaluated. Though all patients had normal intelligence quotient, performance intelligence quotient was significantly lower than verbal intelligence quotient in 2 patients. Both P100 and P1 amplitudes were significantly greater in adrenoleukodystrophy than in controls. The difference between performance intelligence quotient and verbal intelligence quotient exhibited significant correlation with P100 amplitude. Enlargement of visual evoked potentials might be a sign of cerebral involvement preceding the appearance of abnormalities on magnetic resonance imaging. Follow-up of asymptomatic boys with both electrophysiological and neuropsychological tests may serve as an aid for deciding the timing of therapeutic intervention.

Spreading Depression Enhances Human Neocortical Excitability in vitro

Cortical spreading depression (CSD) plays a role in migraine with aura. However, studies of the neuronal effects of CSD in human cortex are scarce. Therefore, in the present study, the effects of CSD on the field excitatory postsynaptic potentials (fEPSP) and the induction of long-term potentiation (LTP) were investigated in human neocortical slices obtained during epilepsy surgery. CSD significantly enhanced the amplitude of fEPSP following a transient suppressive period and increased the induction of LTP in the third layer of neocortical tissues. These results indicate that CSD facilitates synaptic excitability and efficacy in human neocortical tissues, which can be assumed to contribute to hyperexcitability of neocortical tissues in patients suffering from migraine.

The brain is hyperexcitable in migraine

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

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

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

Evaluating the effects of spatial frequency on migraines by using pattern-reversal visual evoked potentials

OBJECTIVE

To clarify the effects of contrast and spatial frequency in patients with migraine by means of pattern-reversal visual evoked potentials (PVEPs).

METHODS

PVEPs were obtained from 14 patients who had migraine without aura (MO), 11 patients who had migraine with aura (MA), and 25 age-matched, healthy controls (CO). PVEPs were binocularly recorded with a reversal rate of 1Hz (2 reversal/s) at 3 spatial frequencies (0.5, 1.0 and 4.0 cpd) at high (98%), medium (83%) and low (29%) contrast. N75, P100 and N135 latency and the amplitudes of P50-N75, N75-P100 and P100-N135 were analyzed.

RESULTS

Increased amplitude of PVEPs in patients with migraines were revealed at 3 different spatial frequencies in all components. The MO and the MA showed increased amplitudes mostly in high contrasts (98%). These findings were detected more at a high spatial frequency (4.0 cpd) than at a low spatial frequency (0.5 cpd). Increased amplitude with prolonged latency of N135 were found both in MO and MA at 4.0 cpd.

CONCLUSIONS

We conclude that pattern stimuli of high contrasts may be particularly effective in uncovering abnormal cortical reactivity which may be modified in the primary and secondary visual cortex in the interictal state of migraine.

SIGNIFICANCE

These findings indicate that there is abnormal visual cortex processing in patients with migraine.

Spinal and cortical spreading depression enhance spinal cord activity

Cortical spreading depression (CSD) has been suggested to underlie some neurological disorders such as migraine. Despite the intensity with which many investigators have studied SD in the brain, only a few studies have aimed to identify SD in the spinal cord. Here we described the main characteristic features of SD in the spinal cord induced by different methods including various spinal cord injury models and demonstrated that SD enhances the spinal cord activity following a transient suppressive period. These findings suggest that SD may play a role in the mechanisms of spinal neurogenic shock, spinal cord injury, and pain. Furthermore, we studied the effect of CSD on the neuronal activity of the spinal cord. CSD was induced via cortical pinprick injury or KCl injection in the somatosensory cortex. CSD did not propagate into the cervical spinal cord. However, intracellular recordings of the neurons in the dorsal horn of C2 segment, ipsilateral to the hemisphere in which CSD was evoked, showed a transient suppression of spontaneous burst discharges, followed by a significant enhancement of the neuronal activity. This indicates a link between a putative cause of the neurological symptoms and the subsequent pain of migraine.

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

Electrophysiological methods may help to unravel some of the pathophysiological mechanisms of migraine. Lack of habituation is the principal and most reproducible interictal abnormality in sensory processing in migraineurs. It is found in evoked potential (EP) studies for every stimulation modality including nociceptive stimuli, and it is likely to be responsible for the increased intensity dependence of EP. We have hypothesized that deficient EP habituation in migraine could be due to a reduced preactivation level of sensory cortices because of hypofunctioning subcortico-cortical aminergic pathways. This is not in keeping with simple hyperexcitability of the cortex, which has been suggested by some, but not all, studies of transcranial magnetic stimulation (TMS). A recent study of the effects of repetitive TMS on visual EP strongly supports the hypothesis that migraine is characterized by interictal cortical hypoexcitability. With regard to pain mechanisms in migraine, electrophysiological studies of trigeminal pathways using nociceptive blink and corneal reflexes have confirmed that sensitization of central trigeminal nociceptors occurs during migraine attacks.

Evoked potentials and transcranial magnetic stimulation in migraine: published data and viewpoint on their pathophysiologic significance

Migraine is a disorder in which central nervous sytem dysfunction might play a pivotal role. Electroneurophysiology seems thus particularly suited to study its pathophysiology. We have extensively reviewed evoked potential and transcranial magnetic stimulation studies performed in migraineurs in order to identify their pathophysiologic significance. Publications available to us were completed by a Medline search. Retrieved and personal data were compared with respect to methodology and interpreted according to present knowledge on cortical information processing. Results are in part contradictory which appears to be method-, patient- and disease- related. Nonetheless, both evoked potential and transcranial magnetic stimulation studies demonstrate that the cerebral cortex, and possibly subcortical structures, are dysfunctioning interictally in both migraine with and without aura. These electrophysiologic abnormalities tend to normalise just before and during an attack and some of them seem to have a clear familial and predisposing character. Besides the studies of magnetophosphenes which have yielded contrasting results, chiefly because the method is not sufficiently reliable, most recent electrophysiologic investigations of cortical activities in migraine favour deficient habituation and decreased preactivation cortical excitability as the predominant interictal dysfunctions. We propose that the former is a consequence of the latter and that it could favour both interictal cognitive disturbances as well as a cerebral metabolic disequilibrium that may play a role in migraine pathogenesis. To summarize, electrophysiologic studies demonstrate in migraine between attacks a cortical, and possibly subcortical, dysfunction of which the hallmark is deficient habituation.

Spatial contrast sensitivity of migraine patients without aura

Visual disturbances are frequent symptoms in migraine. Since there is a possibility of separate damage in the magno- or parvo-cellular visual pathway in migraine patients, we performed a study including the measurement of static and dynamic spatial contrast sensitivity on 15 patients suffering from migraine without aura under photopic and scotopic conditions. Fifteen healthy volunteers without primary headache served as controls. The results revealed a marked decrease in contrast sensitivity at low spatial frequencies in the migraine patients. Spatial contrast sensitivity demonstrated some lateralization, as the sensitivity to low spatial frequencies obtained through separate eyes showed significantly larger side-differences in migraine patients than in control subjects. These findings suggest that the mechanisms responsible for vision at low spatial frequencies are impaired in migraine patients. This might indicate impaired function of the magnocellular pathways in this condition.

Spectral analysis of visual potentials evoked by pattern-reversal checkerboard in juvenile patients with headache

Changes in visual evoked potentials, mainly affecting the amplitude of the major positive wave, are referred to by many authors and are related to the pathophysiological basis of primary headache. We performed both transient pattern-reversal visual evoked potentials and spectral analysis by means of fast Fourier transform of 8-Hz steady-state pattern-reversal visual evoked potentials in 34 children affected with migraine (14 with aura, 20 without aura), and compared them with 14 patients with tension-type headache and 10 healthy subjects. The amplitude of the response to the transient stimulation (P100) was higher and the latency shorter in the patients with headache compared with the controls, but the difference was not statistically significant. The absolute power of the first harmonic (1F) obtained by the spectral analysis of the steady-state stimulation was increased in all the patients with headache compared with the controls, and the increase was significant in patients with migraine. These data seem to confirm the hypothesis of abnormal processing of visual input in migraineurs and could be interpreted as neurophysiological support for the theory that different headache types are related conditions. Furthermore, the spectral analysis of steady-state pattern-reversal visual evoked potentials could be proposed as a test to diagnose migraine.

Visual evoked potential changes in migraine. Influence of migraine attack and aura

OBJECTIVE

To assess the visual evoked potential (VEP) changes in migraines with and without aura.

STUDY DESIGN

A clinical study in which the VEP results of 45 migraineurs (study group) and 22 healthy volunteers (control group) were compared. Of 45 migraineurs, 29 had migraine with aura (MA) and 16 had migraine without aura (MOA), and they were examined both during and between the migraine attacks.

METHODS

The patients and healthy controls underwent VEP assessment. On VEP recording, mono-ocular stimulation was performed by means of the pattern reversal check board. The latencies of N1, P1 and N2, and the N1--P1 amplitude were noted. The following comparisons were made between NI, P1 and N2 latencies and N1--P1 amplitudes of the migraine and control groups; during and between attack the VEP results of the patients with MA and MOA.

RESULTS

The VEP results of the migraineurs and healthy controls were similar (P>0.05). The during attack results of MA, during and between attack results of MOA, and the results of the control group were also similar (P>0.05). N2 latency significantly elongated in patients with MA in the attack free period than it was during the attack (P=0.01), and was also longer than it was in the control group (P=0.01).

CONCLUSIONS

There is involvement of the visual pathway in MA rather than MOA, and differentiation between these subtypes of the migraine disease may be performed on the basis of VEP findings manifesting by the prolongation of the N2 wave latency. This contention should be confirmed by further studies.

Olfactory and trigeminal event-related potentials in migraine

BACKGROUND

Trigeminal/neuronal hyperexcitability and spreading depression activating the trigemino-vascular system are discussed in migraine-pathophysiology. This study investigated trigeminal and olfactory event-related potentials in migraineurs.

METHODS

Nasal chemosensitivity was assessed in 19 female migraineurs with or without aura > 72 h before or after an attack and in 19 healthy females employing event-related cortical potentials (ERPs) after specific trigeminal stimulation of nasal nociceptors with short pulses of CO2, and specific olfactory stimulation with H2S. Odour thresholds and odour identification performance were also tested.

RESULTS

Migraineurs exhibited greater responses to trigeminal stimulation, indicated by significantly larger ERP amplitudes N1. In contrast, olfactory ERP amplitudes P1N1 were significantly smaller in migraineurs. A leave-one-out classification procedure on the basis of these two parameters assigned 76.3% cases correctly. The olfactory ERP amplitude discriminated better between groups than trigeminal ERPs (71.1 vs. 68.4% correct classification).

CONCLUSIONS

Our data suggest trigeminal hyperexcitability in migraineurs. A general increase of nasal chemosensitivity is not supported because of smaller olfactory ERP amplitudes in migraineurs. Olfactory ERPs discriminate better than trigeminal ERPs between migraineurs and controls, emphasizing the significance of the olfactory system in migraine.

[Fast visual categorization and speed of processing in migraine]

It has been suggested that the visual cortex of migraine sufferers is hypersensitive. To test this hypothesis, we compared the speed of visual processing in eight migraine patients (including three with aura) and nine controls performing two categorisation tasks of different complexity. In the complex task developed by Thorpe et al. (1996), subjects had to detect the presence of animals in briefly presented photographs (20 ms). The speed of visual processing was measured by the latency of the differential cerebral activity that appears around 150 ms between target and non-target trials. In the simple task, subjects performed a square/circle categorisation. All subjects were faster (445 ms/497 ms) with a higher rate of success (97%/91%) in the simple task. But in both tasks, the behavioural performance and the associated evoked potentials did not show any difference suggesting a cortical hypersensitivity in migraine sufferers.

Pattern reversal visual evoked potentials in migraine with aura and migraine aura without headache

Pattern reversal visual evoked potentials (PVEPs) were recorded in 20 patients with migraine with aura (MA), 19 patients with migraine without headache (migraine equivalent; ME) during interictal periods, and 34 normal subjects. All migraine patients had hemianopsia or fortification spectra during attacks. In both MA and ME patients of less than 49 years of age, there were significant (p<0.01) differences in amplitude of PVEPs at the mid-occipital and contralateral to visual aura electrode sites compared to normal subjects. Amplitude of PVEPs in MA and ME showed significant (p<0.001) increases when recorded soon after attacks, especially within 10 days. There was a significant (p<0.01) correlation between percentage asymmetries and the duration of illness in both MA and ME. We conclude from our PVEP findings that cortical spreading depression remains the most likely explanation for the migraine visual aura.

Simultaneous recording of pattern reversal electroretinograms and visual evoked potentials in migraine

We recorded full-field pattern reversal electroretinograms (PERGs) and visual evoked potentials (PVEPs) simultaneously in 15 migraine with aura, 14 migraine without aura patients during the interictal period, and in 23 sex- and age-matched normal subjects. All subjects had normal visual fields. The visual aura in all patients was hemianopsia or fortification spectra. Neither migraine group showed significant differences from normal in latency and amplitude of PERGs. In migraine with aura, the amplitudes of PVEPs in classic migraine at the mid-occipital electrode were significantly (p < 0.01) higher than normal. PVEP amplitudes were significantly (p < 0.01) higher on the contralateral side of the aura than the ipsilateral side in both visual aura and normal subjects, but there was no significant difference in latency. This high amplitude and asymmetry of PVEPs may contribute to defective inhibition between interhemispheric visual occipital areas or striate and peristriate areas.