Évaluation électrophysiologique de l’excitabilité corticale dans la migraine

Is Palinopsia in Migraineurs a Phenomenon of Impaired Habituation of Visual Cortical Neurons?

Palinopsia in migraine has been reported recently, which may be due to the dysexcitability of visual cortical neurons. In this cross-sectional study, we report the correlation of neuronal dysexcitability with palinopsia using pattern shift visual evoked potential (PSVEP) in 91 migraineurs and 25 healthy controls. The presence of palinopsia was evaluated using a novel objective method, and revealed more frequent palinopsia in the migraineurs compared to the controls (53 of 91 [58.2%] vs 3 of 25 [12%]; P < .001). Five consecutive blocks of PSVEP were recorded for the evaluation of sensitization and impaired habituation. Amplitudes of N75 and P100 in block 1 were considered for sensitization. Impaired habituation of N75 and P100 was considered if any amplitudes in blocks 2 to 5 were higher than block 1. Impaired habituation was more frequent in migraineurs compared with the controls, and was more marked in wave N75 (81.3% vs 32%; P < .001) than wave P100 (63.7% vs 44%; P = .12). Impaired habituations of wave N75 (81.7% vs 58.9%; P = .008) and wave P100 (71.7% vs 46.4%; P = .008) were more frequent in those with palinopsia compared with those without. There was a lack of suppression of P100 amplitude in block 3 in the palinopsia group compared to the controls. The duration of palinopsia correlated with the extent of impaired habituation of N75. It can be concluded that the impaired habituation of PSVEP waveforms is a biomarker of palinopsia in migraine.

Perivascular neurotransmitters: Regulation of cerebral blood flow and role in primary headaches

In order to understand the nature of the relationship between cerebral blood flow (CBF) and primary headaches, we have conducted a literature review with particular emphasis on the role of perivascular neurotransmitters. Primary headaches are in general considered complex polygenic disorders (genetic and environmental influence) with pathophysiological neurovascular alterations. Identified candidate headache genes are associated with neuro- and gliogenesis, vascular development and diseases, and regulation of vascular tone. These findings support a role for the vasculature in primary headache disorders. Moreover, neuronal hyperexcitability and other abnormalities have been observed in primary headaches and related to changes in hemodynamic factors. In particular, this relates to migraine aura and spreading depression. During headache attacks, ganglia such as trigeminal and sphenopalatine (located outside the blood-brain barrier) are variably activated and sensitized which gives rise to vasoactive neurotransmitter release. Sympathetic, parasympathetic and sensory nerves to the cerebral vasculature are activated. During migraine attacks, altered CBF has been observed in brain regions such as the somatosensory cortex, brainstem and thalamus. In regulation of CBF, the individual roles of neurotransmitters are partly known, but much needs to be unraveled with respect to headache disorders.

A 'complex' of brain metabolites distinguish altered chemistry in the cingulate cortex of episodic migraine patients

Despite the prevalence of migraine, the pathophysiology of the disease remains unclear. Current understanding of migraine has alluded to the possibility of a hyperexcitable brain. The aim of the current study is to investigate human brain metabolite differences in the anterior cingulate cortex (ACC) during the interictal phase in migraine patients. We hypothesized that there may be differences in levels of excitatory neurotransmitters and/or their derivatives in the migraine cohort in support of the theory of hyperexcitability in migraine. 2D J-resolved proton magnetic resonance spectroscopy (¹H-MRS) data were acquired on a 3 Tesla (3 T) MRI from a voxel placed over the ACC of 32 migraine patients (MP; 23 females, 9 males, age 33 ± 9.6 years) and 33 healthy controls (HC; 25 females, 8 males, age 32 ± 9.6 years). Amplitude correlation matrices were constructed for each subject to evaluate metabolite discriminability. ProFit-estimated metabolite peak areas were normalized to a water reference signal to assess subject differences. The initial analysis of variance (ANOVA) was performed to test for group differences for all metabolites/creatine (Cre) ratios between healthy controls and migraineurs but showed no statistically significant differences. In addition, we used a multivariate approach to distinguish migraineurs from healthy subjects based on the metabolite/Cre ratio. A quadratic discriminant analysis (QDA) model was used to identify 3 metabolite ratios sufficient to minimize minimum classification error (MCE). The 3 selected metabolite ratios were aspartate (Asp)/Cre, N-acetyl aspartate (NAA)/Cre, and glutamine (Gln)/Cre. These findings are in support of a ‘complex’ of metabolite alterations, which may underlie changes in neuronal chemistry in the migraine brain. Furthermore, the parallel changes in the three-metabolite ‘complex’ may confer more subtle but biological processes that are ongoing. The data also support the current theory that the migraine brain is hyperexcitable even in the interictal state.

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3 T MRI was used to acquire 2D J-resolved proton magnetic resonance spectroscopy.

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Metabolite alterations are reported in the anterior cingulate cortex of episodic migraineurs.

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The complex of metabolites may reflect multiple chemical changes in migraineurs.

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The observed chemical changes support the theory that the brain of migraineurs is hyperexcitable.

[A causative role of vasodilation in migraine? No]

INTRODUCTION

The hypothesis that migraine pain is caused by vasodilation has been challenged by clinical and experimental evidence.

STATE OF ART

The most convincing arguments against the vascular hypothesis come from neuroimaging data. Magnetic resonance imaging studies show that spontaneous migraine attacks are not accompanied by extracranial vasodilation, and by only slight dilation of the intracranial arteries. Pharmacologically-induced migraine attacks also provide further evidence against the role of vasodilation in migraine. Vasodilators such as sildenafil and nitroglycerine trigger attacks without dilation of the middle cerebral artery diameter, whereas VIP (vasoactive intestinal peptide) markedly dilates intra- and extracranial arteries but does not induce migraine attacks. Clinical studies also show a lack of correspondence between the subjective experience of throbbing headache and the arterial pulse. Moreover, many acute anti-migraine agents are not vasoconstrictors.

PERSPECTIVES

Further studies are necessary to clarify the mechanisms of migraine headache generation.

CONCLUSIONS

Contrary to a longstanding and widespread belief, vasodilatation is neither sufficient nor necessary to cause migraine headache and is probably an epiphenomenon.