Objective: To examine visual cortical excitability in persons with migraine using transcranial magnetic stimulation (TMS) over an extrastriate area of the brain, area V5.
Background: Previous studies found that persons with migraine have a lower phosphene threshold than healthy control subjects with TMS delivered over the primary visual cortical area V1. The result suggests that the occipital cortex in migraineurs between migraine attacks is hyperexcitable. However, it is not known whether interictal cortical hyperexcitability is also present in areas of the association visual cortex.
Method: To investigate this, single-pulse TMS was delivered over visual area V5, the motion cortex, to 16 persons with migraine and visual aura, nine migraineurs without visual aura, and 16 healthy control subjects. TMS was delivered at intensities ranging from 30 to 100% of maximum stimulator output or until the participant reported seeing phosphenes (visual illusions characterized by flashes of light). Thresholds to phosphenes were obtained for each participant using a staircase procedure.
Result: Significantly lower phosphene thresholds for TMS delivered over V5 were found in migraineurs as compared with control subjects. Qualitatively, the migraineurs' experience of phosphenes were more vivid, florid, and sustained compared with that of control subjects.
Conclusion: Results of this study indicate that hyperexcitability of the visual cortex in migraine goes beyond visual area V1 and demonstrates for the first time a significant difference in threshold for excitability of visual area V5 in persons with migraine.