The occipital cortex is hyperexcitable in migraine: experimental evidence.
OBJECTIVE
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.
Department of Neurology, Henry Ford Health Sciences Center, 2799 West Grand Boulevard, Detroit, MI 48202-2689, USA.
S K
SK
Aurora
Y
Y
Cao
S M
SM
Bowyer
K M
KM
Welch
D000328:Adult; D013181:Cortical Spreading Depression / Q000502:physiology; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D008881:Migraine Disorders / Q000503:physiopathology*; D009778:Occipital Lobe / Q000503:physiopathology*; D009903:Optical Illusions / Q000502:physiology; D010719:Phosphenes / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D014796:Visual Perception / Q000502:physiology