Orientation discrimination thresholds in migraine: a measure of visual cortical inhibition

Orientation discrimination is a visual task dependent on inhibitory mechani sms in the visual cortex. In this study, orientation discrimination thresho lds for bar and grating patterns were measured at two visual field location s in subjects with migraine with (n=20) and without aura (n=20) and in migr aine-free control subjects (n=20). No statistically significant differences were found between migraine groups and the control group on either task at foveal or peripheral visual field locations. No significant correlations w ere found between psychophysical thresholds and age, total lifetime auras o r total lifetime migraine episodes. However, a trend was seen toward slight ly impaired performance on the two foveal tasks in a subgroup of subjects w ith the highest total lifetime aura count. Thus we have found no convincing evidence that impaired cortical inhibitory mechanisms are a predisposing c haracteristic in migraine, but cannot rule out the possibility that cortica l inhibitory mechanisms may be adversely affected by repeated visual auras.