Suppression of perception in migraine - Evidence for reduced inhibition inthe visual cortex

Background: Results from transcranial magnetic stimulation (TMS) studies of visual cortex have confirmed visual cortical hyperexcitability in patients with migraine. It has been speculated that this may be due to deficient in tracortical inhibitory tone. However, the TMS induction of phosphenes relie s on the reporting of a subjective experience, and may thus be subject to b ias. Methods: Seven migraineurs with visual aura and seven sex- and age-mat ched controls were studied. Fifty-four different three-letter combinations were briefly displayed and followed by a magnetic pulse at 40, 70, 100, 130 , 160, and 190 msec. Subjects were required to report as many letters as th ey thought they had recognized. Results: In the migraine group, the mean pr oportion of correctly identified letters was significantly higher at 100 ms ec, as was the proportion of trials with two or three letters correctly rep orted. The time window in which perceptual suppression could be introduced was narrower in migraineurs compared to controls. Conclusion: These finding s suggest that inhibitory systems are activated to a lesser extent by TMS p ulses in patients. This observation is in agreement with the hypothesized d eficiency of intracortical inhibition of the visual cortex, at least in mig raineurs with aura.