Abstract
Migraine is a disabling primary brain disorder that affects around 10% of the global population. Migraine costs the economy, in the European Union alone, around €20 billion a year. Visual symptoms (e.g. aura) are common in migraine and it is now established that subtle visual changes exist in patients even between attacks. Why vision is altered and the cause and consequences of visual aura remain elusive.This work applied psychophysical techniques and computational models to examine the hypothesis for an imbalance of cortical excitation and inhibition in migraine patients with and without aura.
Visual performance was examined firstly, by testing luminance contrast detection with and without added visual luminance noise. Secondly, the strength of long-range inhibitory interactions was examined by measuring the duration of twinkling noise afterimages using an artificial scotoma paradigm. Thirdly, global shape discrimination thresholds were tested to investigate whether an imbalance might also exist in extra striate areas. Fourthly, global motion direction detection was tested using classification images. A novel model was developed to extract performance and strategy for this task within a noisy environment. Finally, three short experiments investigated local and global shape and global motion in order to try to identify an approach that might be developed as a monitoring tool in migraine.
Findings suggest that migraine-with-aura subjects have noise exclusion deficits, which may be due to impaired inhibitory mechanisms in striate cortex. Migraineurs exhibit shorter afterimages compared to controls suggesting impaired inhibitory longrange interactions. Migraine-with-aura subjects showed raised discrimination thresholds in a shape detection task suggesting an abnormal neural representation of global shapes in extra striate areas. Migraineurs with aura also showed weakened suppression in the periphery when detecting global motion direction compared to controls. Migraineurs with aura appeared to be prone to higher internal noise and higher sampling efficiency. The short test examining global form detection found poorer performance in migraineurs without aura compared to the other two groups.
The results point to weakened inhibitory mechanisms, resulting in hyperexcitability, and higher internal noise in migraineurs-with-aura. These could be pursued from V1 to V5. Migraine-without-aura subjects showed a trend towards similarly altered cortical function.
| Date of Award | 2011 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Velitchko Manahilov (Supervisor), Gael Gordon (Supervisor) & Gordon Dutton (Supervisor) |