Schoenen and his colleagues have long argued that migraineurs have a deficit in habituation that is revealed in the cortical pattern-reversal visual evoked potential (PR-VEP) during extended viewing of a high contrast phase-reversing checkerboard stimulus ( 12– 14) but see ( 15)). Moreover, an extensive electrophysiological literature has clearly indicated that it is repetitive stimulation, not a brief stimulus, that reveals the truly striking differences between migraineurs and individuals with no migraine history. However, it has long been clear that the problem for migraineurs comes principally from higher contrast stimuli, not from stimuli that are barely detectable. Most psychophysical work on flicker or temporal frequency has focused on detection thresholds – the minimum contrast that can be detected against a homogeneous field - and there are mixed results as to whether migraineurs differ from controls ( 9– 11). ![]() In a laboratory test of flicker aversion thresholds, we have repeatedly found that migraineurs choose to abort a flickering screen at lower contrasts than healthy controls who, in many cases, are not bothered at all by such a stimulus even at maximum contrast. While many find the flickering sunlight to be mildly irritating, migraineurs find this much more aversive ( 6). A good illustration of this is driving through an avenue of trees at sunset when the sun falls directly behind the tree line. Flicker is particularly bothersome to individuals with migraine. In particular, spatial and temporal frequencies close to the peak of the human contrast sensitivity function (3–5 c/deg stripes and 10–20 Hz flicker) are most aversive ( 2– 5). However, interictal visual discomfort has been reported to be linked not only to light intensity, but also to specific spatial and temporal properties of the visual input. ![]() While most extreme during migraine episodes, photophobia may also afflict migraineurs between episodes. Photophobia (light avoidance) is characterized by hypersensitivity or intolerance to light, such that moderate intensities are perceived as uncomfortable and even painful ( 1). ![]() The defining visual features of migraine are photophobia and, in a subpopulation of migraineurs, visual aura which typically precedes headache onset.
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