Visual contrast gain control in migraine: measures of visual cortical excitability and inhibition

The present study examined the extent to which migraineurs demonstrate inte rictal Visual cortical hyperexcitability as a result of poor inhibitory con trol in the visual system. We employed a well-established psychophysical me asure of inhibition, visual contrast gain control. The task involved detect ing a briefly presented target that was superimposed on a highly excitable high contrast masking pattern. The strength of inhibition was assessed by c omparing target detection thresholds with and without the operation of gain controls. Migraineurs with and without aura (n = 25, n = 22, respectively) were compared with those with no history of migraine (n = 25). Our results do not indicate a loss of inhibition in migraine; the strength of inhibito ry feedback contrast gain controls was similar between migraineurs and cont rols. We did however, find a statistically greater masking effect in migrai neurs compared with controls in the zero delay condition, suggesting cortic al hyperexcitability in migraine. Possible mechanisms of cortical hyperexci tability are discussed in light of the results.