Neurophysiology of Migraine with Aura
In this chapter, we review the findings obtained by neurophysiological studies in migraine with aura (MA).
Spontaneous electroencephalography activity in MA is characterized by abnormalities in alpha rhythm power and symmetry, and the presence of slowing, and increased, information flow in a wide range of frequency bands. Evoked potential (EP) studies indicate the occurrence of increased grand-average cortical response amplitudes, interhemispheric response asymmetry, as well as deficient habituation to any kind of repetitive sensory stimulation, in MA patients.
Transcranial magnetic stimulation (TMS) methods applied in MA confirm abnormalities in cortical responsivity, such as greater motor evoked potential (MEP) amplitude, lower threshold for phosphene production, and paradoxical effects induced by depressing or enhancing repetitive TMS. Brainstem reflex studies indicate a deficit of blink reflex habituation in MA. Mild abnormalities of neuromuscular transmission shown by single-fibre electromyography were more pronounced in migraineurs with aura, and positively correlated to the complexity of their aura. The few studies performed in patients during the aura described suppression of evoked potentials, desynchronization in extrastriate areas and the temporal lobe, and large variations in direct current potentials using magnetoelectroencephalography. In contrast, patients affected by familial hemiplegic migraine had opposite neurophysiological patterns in comparison with patients suffering from the common forms of migraine.