Increased visual after-effects following pattern adaptation in migraine: a lack of intracortical excitation?

Much research on visual function in migraine has examined early aspects of visual processing, often using detection or discrimination measures and stimuli reported to trigger an attack, e.g. striped patterns or flickering lights. Differences between people with and without migraine have been attributed to abnormal cortical processing in migraine, variously described by interictal hyperexcitability, heightened responsiveness, a lack of habituation and/or a lack of intra-cortical inhibition. Here, two experiments are presented that explore a uniquely cortical phenomenon, pattern or contrast adaptation, one using the motion after-effect, one the tilt after-effect. Pattern adaptation reflects specific interactions between groups of neurones and is therefore ideally suited to address proposed models of cortical function in migraine. These models lead to specific predictions in an adaptation study: there should be smaller effects in people with migraine than in people without. The results from both adaptation experiments, however, revealed larger effects in migraine sufferers than in headache-free control subjects. There were no differences between migraine subgroups classified according to the presence or absence of aura. These results are discussed in terms of models of cortical function in migraine.