The occipital cortex is hyperexcitable in migraine: experimental evidence.

OBJECTIVES

Threshold for generation of magnetophosphenes has been reported to be lower in migraine. We compared the threshold for eliciting phosphenes by transcranial magnetic stimulation and the ability to visually trigger headache in a select group of individuals with migraine with and without aura to normal controls.

METHODS

Transcranial magnetic stimulation was performed using the Cadwell MES-10 stimulator. A circular coil, 9.5 cm in diameter, was applied to the occipital scalp (7 cm above the inion). Stimulator intensity was increased in 10% increments until subjects reported visual phenomena or 100% intensity was reached. Stimulator intensity was then fine-tuned to determine the threshold at which phosphenes were seen. In the same subjects, visual stimulation was given in 3.0 T MRI and if a headache occurred the response was recorded.

RESULTS

Fifteen subjects with migraine were compared to 8 controls. A significant proportion of the migraineurs (86.7%) developed phosphenes compared to the controls (25%) (P = .006). The probability of triggering a headache was also higher in the migraineurs (53%); no headache was triggered in the controls (P = .019). A significant correlation was found between the threshold for phosphenes on transcranial magnetic stimulation and visually triggered headache (P = .002). When only migraine was considered, there was again a significant trend (P = .084).

CONCLUSIONS

There is a difference in threshold for excitability of occipital cortex in migraineurs and controls. The hyperexcitable visual cortex in migraine is predisposed to visually triggered headache.