Abstract
The pupil constricts to illusory brightness, presumably mediated by a cortical mechanism. People with migraine with aura (MwA) have greater discomfort and cortical response to visual stimuli. We tested if people with MwA have an enhanced pupil response to illusory brightness as compared to migraineurs without aura (MwoA) and headache-free controls (HaF). Our pre-registered study is of 15 subjects from each of the 3 headache diagnostic categories. Pupil responses are recorded while subjects view many, 1s presentations of three different stimuli, equated in integrated spatial luminance. Each radially symmetric, annular stimulus has an identical, lighter center, and a varying, darker surround. The surround is either Uniform, or has a linear slope that increases towards the periphery (Halo), or the center (Glow). Enhancement of the perceived brightness of the stimulus center has been reported for the Glow and Halo stimuli (Tamura 2016 JoV). The mean % change in pupil size is computed for each stimulus type for each subject. We report here interim results from the 40 subjects studied to date. Across all subjects, as compared to the response to Uniform (6.4% constriction), there was a greater constriction to both Glow (9.1%, p=0.06) and Halo (8.2%, p=0.026); Glow and Halo responses were not significantly different (p=0.23). In a pre-registered test, MwA subjects had a greater difference between the Glow and Uniform stimuli (4.0%) than did the HaF subjects (1.9%), but this difference is not significant (p=0.24); similar to HaF, MwoA subjects had a small difference between the Glow and Uniform stimuli (2.3%). The pattern of responses across subject groups for Halo vs. Uniform stimuli is quite similar. Our interim conclusions are that illusory brightness enhances pupil constriction, and that we have not yet rejected the possibility that this effect may be greater in people with migraine with aura.