Modulation of visual evoked potentials by high-frequency repetitive transcranial magnetic stimulation in migraineurs

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 25min after 10Hz 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.