Neurophysiological features of the migrainous brain

Migraine is a disorder in which central nervous system (CNS) dysfunction might play a pivotal role. As there are no consistent structural disturbances, clinical neurophysiology methods seem particularly suited to study its pathophysiology. This chapter will focus on a review of neurophysiological studies that have provided an insight into migraine pathogenesis. The results are in part contradictory, which may be due to the methodology, patient selection or timing of study. Nonetheless, quantitative electroencephalography and magnetoencephalography recordings during migraine attacks provide strong, though indirect, evidence favouring the occurrence of spreading cortical depression during attacks of migraine with, and possibly without, aura. Evoked cortical potential and nociceptive blink reflex studies demonstrate that lack of habituation during repetitive stimulation is a reproducible CNS dysfunction interictally in both migraine with and without aura. Transcranial magnetic stimulations show excitability changes of the visual cortex. The interictal migrainous CNS dysfunction is likely to play a role in migraine pathogenesis, has a familial character and undergoes periodic modulations with quasi-normalisation just before, during an attack and after treatment with certain prophylactic agents. In addition, neurophysiological methods have revealed subclinical abnormalities of cerebellar function and neuromuscular transmission, which may improve phenotyping of migraineurs for genetic and therapeutic studies.