Visual paired-pulse stimulation reveals enhanced visual cortex excitability in migraineurs.
ABSTRACT 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.
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ABSTRACT: Objective High-frequency repetitive transcranial magnetic stimulation (rTMS) modulates cortical excitability. We investigated its effect on visual evoked potentials (VEPs) in migraine. Methods Thirty-two headache-free controls (CO), 25 interictal (MINT) and 7 preictal migraineurs (MPRE) remained after exclusions. VEPs to 8’ and 65’ checks were averaged in six blocks of 100 single responses. VEPs were recorded before, directly after and 25 minutes after 10 Hz rTMS. The study was blinded for diagnosis during recording and for diagnosis and block number during analysis. First block amplitudes and habituation (linear amplitude change over blocks) were analysed with repeated measures ANOVA. Results With 65’ checks, N70-P100 habituation was reduced in MINT compared to CO after rTMS (p = 0.013). With 8’ checks, habituation was reduced in MPRE compared to MINT and CO after rTMS (p < 0.016). No effects of rTMS on first block amplitudes were found. Conclusion RTMS reduced habituation only in migraineurs, indicating increased responsivity to rTMS. The magnocellular visual subsystem may be affected interictally, while the parvocellular system may only be affected preictally. Significance Migraineurs may have increased responsiveness to rTMS because of a cortical dysfunction that changes before a migraine attack.Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 01/2014; · 3.12 Impact Factor
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ABSTRACT: IntroductionNeurophysiological studies point to altered cortical neuronal excitability in migraine patients.State of artBetween attacks, migraine brain seems to be “hyperresponsive” to repetitive stimuli, as suggested by evoked potential studies that show a lack of habituation to sensory stimuli. Transcranial magnetic stimulation suggests an impairment of intracortical inhibitory circuits in migraine, especially in migraine with aura. Controversial results are obtained in migraineurs without aura. Repetitive transcranial magnetic stimulation also shows in migraine with aura a paradoxical enhancement of intracortical facilitation by low frequency stimulation and greater increased facilitatory mechanisms by high-frequency stimulation. Importantly, cortical excitability level fluctuates over time in relation to the migraine cycle. The interictal lack of habituation to sensory stimuli normalizes before and during a migraine attack. Changes of cortical excitability consistent with the theory of cortical spreading depression are also observed during migraine aura with magnetoencephalography.PerspectivesThe exact role of cortical excitability changes in migraine pathophysiology and possibly in chronic migraine is still unknown. Further studies are also necessary to clarify the role of migraine preventive drugs on brain excitability.Conclusions In this review, the results of neurophysiological studies conducted in migraine patients will be described and the associated pathophysiological hypotheses will be discussed.Revue Neurologique 05/2013; 169(5):427–435. · 0.51 Impact Factor