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ABSTRACT: Patients with migraine are averse to certain visual stimuli, such as flicker and striped patterns that evoke paroxysmal EEG activity in patients with photosensitive epilepsy. Migraineurs demonstrate a hyper-responsiveness to such stimuli, and there is debate as to whether the aversion and hyper-responsiveness are due to a hyperexcitability of the cortex similar to that in patients with photosensitive epilepsy. In these patients grating patterns with certain spatial characteristics can be epileptogenic, depending critically on their movement. If the contours of the grating drift continually, the grating is not epileptogenic, but if the contours are static or if their direction is repeatedly and rapidly reversed so as to vibrate, the grating then becomes highly epileptogenic.
We compared aversion to vibrating, drifting and static gratings in migraineurs and controls. The contrast of each grating was gradually increased, but only until the participant felt discomfort, so as to obtain a contrast threshold for aversion with minimal exposure.
Migraineurs had lower thresholds than the control group, indicating greater aversion. For both groups the threshold was higher (aversion was lower) for static than for both types of moving gratings. The drifting gratings were more aversive than the vibrating gratings when both groups were combined.
The findings suggest that the aversion shown by migraineurs is not attributable to a cortical hyperexcitability similar to that in photosensitive epilepsy.
Cephalalgia 02/2012; 32(3):236-40. · 3.43 Impact Factor
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Cephalalgia 03/2009; · 3.43 Impact Factor
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ABSTRACT: Cortical hyperexcitability in migraine could arise from abnormally weak inhibition or from strengthened intracortical excitatory mechanisms. The present study employed binocular rivalry to differentiate between these possibilities. Rivalry between static oriented grating patterns was examined in migraine with aura (MA), migraine without aura (MoA) and headache-free control participants. A non-significant trend toward elevated mean dominance intervals (monocular percepts, in seconds) was seen in both migraine groups at all contrasts. Second, significant interocular differences in rivalry dominance durations were seen in the MoA group compared with controls; this difference also approached significance in the MA group. Finally, both MA and MoA exhibited significantly greater visual discomfort than the control group in the presence of both static stripes and flickering visual stimuli. The rivalry results provide no support for weakened intracortical inhibition in migraine. Optical or neural precortical differences in the eyes' input strengths paired with enhanced recurrent cortical excitation can explain these findings.
Cephalalgia 10/2008; 28(12):1327-38. · 3.43 Impact Factor
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ABSTRACT: Migraine is a very common disorder occurring in 20% of women and 6% of men. Central neuronal hyperexcitability is proposed to be the putative basis for the physiological disturbances in migraine. Since there are no consistent structural disturbances in migraine, physiological and psychophysical studies have provided insight into the underlying mechanisms. This is a review of the neurophysiological studies which have provided an insight to migraine pathogenesis supporting the theory of hyperexcitability.
Cephalalgia 01/2008; 27(12):1442-53. · 3.43 Impact Factor
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ABSTRACT: The purpose of this study was to examine basic ocular motor function in individuals with migraine. We used an infrared eye-tracking system to measure horizontal smooth pursuit to a sinusoidal target, saccades to horizontal target displacements of 5-20 degrees , and the stability of fixation in 19 migraine without aura (MoA), 19 migraine with aura (MA) and 19 headache-free control (C) subjects. Eye movement measurements were made at two target displacement rates and against both homogeneous grey and patterned backgrounds. We found no statistically significant differences between migraine and control subjects in any of the eye movement parameters measured, but did find highly significant effects of both target speed and background pattern in all groups. Our results do not provide support for subclinical cerebellar impairment in migraineurs, and do provide evidence that previously described visual abnormalities in migraine are not artefacts of abnormal fixation or eye movements.
Cephalalgia 07/2006; 26(6):660-71. · 3.43 Impact Factor
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Australian Journal Of Psychology. 01/2005; 57:76-76.
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Australian Journal Of Psychology. 01/2005; 57:77-77.
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Vision Sciences SocietyVision Sciences Society, Sarasota, Florida; 01/2004
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Perception 01/2002; 31:56. · 1.31 Impact Factor
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Investigative Ophthalmology & Visual Science. 01/2002; 43:U1349-U1349.
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Perception 01/2002; 31:92-92. · 1.31 Impact Factor
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Perception 01/2002; 31:56-56. · 1.31 Impact Factor
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Perception 01/2002; 31:92. · 1.31 Impact Factor
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Investigative Ophthalmology & Visual Science. 01/2002;
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Journal of Vision. 01/2002;
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ABSTRACT: In the classic oblique effect contrast detection thresholds, orientation discrimination thresholds, and other psychophysical measures are found to be smallest for vertical or horizontal stimuli and significantly higher for stimuli near the +/-45 degrees obliques. Here we report a novel inverse oblique effect in which thresholds for detecting translational structure in random dot patterns [Glass, L. (1969). Moiré effect from random dots. Nature, 223, 578-580] are lowest for obliquely oriented structure and higher for either horizontal or vertical structure. Area summation experiments provide evidence that this results from larger pooling areas for oblique orientations in these patterns. The results can be explained quantitatively by a model for complex cells in which the final filtering stage in a filter-rectify-filter sequence is of significantly larger area for oblique orientations.
Vision Research 07/2001; 41(14):1749-53. · 2.41 Impact Factor
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ABSTRACT: To measure the perceived rate of flicker (temporal frequency) observed during visual auras.
The flickering or scintillating quality of aura elements is a commonly described characteristic of visual migraine auras. Hypotheses about the neural mechanisms involved in aura have rarely taken this feature into account, perhaps because of a lack of quantitative data on this aspect of the aura. While a rate of 10 Hertz had been suggested in the literature, estimates have been speculative due to the difficulty of judging temporal frequencies subjectively.
Eleven participants were given portable devices that contained an adjustable light-emitting diode with which to match the flickering of their auras. Observers were asked to make flicker matches at two time points so that rate change during aura progression could be analyzed.
Data were obtained for 36 aura episodes. The mean rate of flicker across individuals was 17.8 Hertz. Rates varied widely between individuals, but were more consistent across multiple episodes in the same observer. Rate of flicker did not appear to relate to aura side or type, or to individual characteristics such as migraine history. When episodes were analyzed for change in flicker rate over time, patterns of increase (n = 7), decrease (n = 4), and no change (n = 22) were all observed.
When measured with an objective task, aura scintillation rates were found to be somewhat higher than previous anecdotal observations had suggested. These data are discussed in the context of two competing hypotheses concerning the neural mechanism underlying the flicker percept during migraine aura.
Headache The Journal of Head and Face Pain 02/2001; 41(1):40-8. · 2.52 Impact Factor
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Investigative Ophthalmology & Visual Science. 01/2001; 42(4):3928.
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ABSTRACT: The ventral form vision pathway of the primate brain comprises a sequence of areas that include V1, V2, V4 and the inferior temporal cortex (IT) [1]. Although contour extraction in the V1 area and responses to complex images, such as faces, in the IT have been studied extensively, much less is known about shape extraction at intermediate cortical levels such as V4. Here, we used functional magnetic resonance imaging (fMRI) to demonstrate that the human V4 is more strongly activated by concentric and radial patterns than by conventional sinusoidal gratings. This is consistent with global pooling of local V1 orientations to extract concentric and radial shape information in V4. Furthermore, concentric patterns were found to be effective in activating the fusiform face area. These findings support recent psychophysical [2,3] and physiological [4,5] data indicating that analysis of concentric and radial structure represents an important aspect of processing at intermediate levels of form vision.
Current Biology 12/2000; 10(22):1455-8. · 9.65 Impact Factor
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ABSTRACT: The present study examined the extent to which migraineurs demonstrate interictal visual cortical hyperexcitability as a result of poor inhibitory control in the visual system. We employed a well-established psychophysical measure of inhibition, visual contrast gain control. The task involved detecting a briefly presented target that was superimposed on a highly excitable high contrast masking pattern. The strength of inhibition was assessed by comparing target detection thresholds with and without the operation of gain controls. Migraineurs with and without aura (n=25, n=22, respectively) were compared with those with no history of migraine (n=25). Our results do not indicate a loss of inhibition in migraine; the strength of inhibitory feedback contrast gain controls was similar between migraineurs and controls. We did however, find a statistically greater masking effect in migraineurs compared with controls in the zero delay condition, suggesting cortical hyperexcitability in migraine. Possible mechanisms of cortical hyperexcitability are discussed in light of the results.
Cephalalgia 04/2000; 20(2):74-84. · 3.43 Impact Factor
