Pattern adaptation is a cortical phenomenon that reflects specific interactions between groups of neurones (described further below) and is therefore well suited to assessing proposed models of cortical function in migraine. Here, two experiments are presented that explore a different aspect of visual processing: pattern or contrast adaptation. The abnormality has been described as interictal hyperexcitability, heightened responsiveness, a lack of habituation and/or a lack of intra-cortical inhibition.
Coleston et al., 1994 Oelkers et al., 1999 McKendrick et al., 2000). In general, these results have been attributed to abnormal cortical processing in migraine, although there is also some evidence for pre-cortical involvement (e.g. Differences have equally been reported with suprathreshold measures such as increased visual discomfort when viewing striped patterns and altered perceived suprathreshold contrast ( Wilkins et al., 1984 Marcus and Soso, 1989 Khalil, 1991 Shepherd, 2000). For example, differences between people with and without migraine have been reported using tasks that assess sensitivity to temporal contrast (flickering light), spatial contrast (striped patterns), colour and orientation ( Khalil, 1991 Coleston et al., 1994 Coleston and Kennard, 1995 Wray et al., 1995 Shepherd, 1999, 2000 McKendrick et al., 2000 Palmer et al., 2000 but see also Wilkinson and Crotogino, 2000). Previous research has predominantly examined early aspects of visual processing, often using threshold detection or discrimination measures and the very stimuli reported to trigger an attack.
One objective has been to determine the origin of any differences and their relevance to the pathophysiology of the condition, or to develop tests that have clinical use. Various aspects of visual processing have been investigated in migraine due in part to the distinctive visual disturbances that may precede or accompany the headache, and in part to reports that visual stimuli can trigger an attack. MAE = motion after-effect, MO = migraine without aura, NVA = migraine with non-visual aura, TAE = tilt after-effect, VA = migraine with visual aura Introduction These results are discussed in terms of models of cortical function in migraine. There were no differences between migraine subgroups classified according to the presence or absence of aura. The results from both adaptation experiments, however, revealed larger effects in migraine sufferers than in headache-free control subjects. These models lead to specific predictions in an adaptation study: there should be smaller effects in people with migraine than in people without. Pattern adaptation reflects specific interactions between groups of neurones and is therefore ideally suited to address proposed models of cortical function in migraine. 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. 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. 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.
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