Difference of steady-state visual evoked potentials in classic and common migraine.

The present study was designed to find evidence for the neural hypothesis of migraine and to evaluate possible interictal differences in the two varieties of migraine by electrophysiological means. Steady-state visual evoked potentials (SVEPs) in response to sinusoidally modulated light were measured in 20 patients with classic migraine and compared with those of 30 common migraineurs and 49 reference subjects. SVEPs to stimuli at 10-24 Hz were recorded occipitally from a pair of midline electrodes and, in classic migraineurs and controls, additionally from left and right occipital areas. The response was processed by the Fast Fourier Transform and automatically analysed. The fundamental component of the midline response to medium frequency stimuli (16-22 Hz) appeared normal in patients with classic migraine, contrary to an augmented response in common migraineurs (ANOVA between groups, P = 0.006). In classic migraine the 2nd harmonic component was attenuated (P less than 0.01 at 18-20 Hz) and the amount of strong interhemispheric f1 asymmetries was increased in about half of the patients. The groups also diverged significantly in the SVEP dynamics during stimulation. The results support the hypothesis of a primary neural disorder in both types of migraine. Different sites and mechanisms of brain dysfunction in classic and common migraine are suggested. Hypothetical neuroanatomical correlates for the abnormalities are presented.