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

Orientation discrimination is a visual task dependent on inhibitory mechanisms in the visual cortex. In this study, orientation discrimination thresholds for bar and grating patterns were measured at two visual field locations in subjects with migraine with (n = 20) and without aura (n = 20) and in migraine-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 were found between psychophysical thresholds and age, total lifetime auras or total lifetime migraine episodes. However, a trend was seen toward slightly impaired performance on the two foveal tasks in a subgroup of subjects with the highest total lifetime aura count. Thus we have found no convincing evidence that impaired cortical inhibitory mechanisms are a predisposing characteristic in migraine, but cannot rule out the possibility that cortical inhibitory mechanisms may be adversely affected by repeated visual auras.