J Crotogino1, A Feindel, F Wilkinson. 1. Department of Psychology, McGill University, 1205 Dr. Penfield Avenue, Montreal, Quebec H3A 1B1, Canada.
Abstract
OBJECTIVE: To measure the perceived rate of flicker (temporal frequency) observed during visual auras. BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.
OBJECTIVE: To measure the perceived rate of flicker (temporal frequency) observed during visual auras. BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.