Abstract and Introduction
The mechanisms underlying the initiation and propagation of the migraine aura, and the visual percept that is produces, remain uncertain. The objective of this study was to characterize and quantify a large number of visual auras recorded by a single individual over nearly two decades to gain insight into basic aura mechanisms. An individual made detailed drawings of his visual percept of migraine aura in real time during more than 1000 attacks of migraine aura without headache over 18 years. Drawings were made in a consistent fashion documenting the shape and location of the aura wavefront or scotoma in the visual field at one minute intervals. These drawings were digitized and the spatial and temporal features of auras were quantified and analysed. Consistent patterns of aura initiation, propagation and termination were observed in both right and left visual fields. Most aura attacks originated centrally (within 10° eccentricity), but there were also other distinct sites of initiation in the visual field. Auras beginning centrally preferentially propagated first through lower nasal field (69–77% of all auras) before travelling to upper and temporal fields, on both sides. Some auras propagated from peripheral to central regions of the visual field—these typically followed the reverse path of those travelling in the opposite direction. The mean velocity of the perceived visual phenomenon did not differ between attacks starting peripherally and centrally. The estimated speed of the underlying cortical event (2–3 mm/min) was in the same range as has been previously reported by others. Some auras had limited propagation and spontaneously 'aborted' after a few minutes, despite being initiated in similar locations to those that spread throughout the entire visual field. The visual percept of the aura changed corresponding with the presumed propagation from the V1 to the V2 region of the occipital cortex. In some cases the visual percept disappeared for several minutes before reappearing in a distant location, providing direct evidence that the aura can be clinically 'silent'. These results indicate that there can be multiple distinct sites of aura initiation in a given individual and suggest that the spatial pattern of propagation in the occipital cortex is non-concentric with a variable extent of propagation. The visual percept of migraine aura changes depending on the region of the occipital cortex that is involved.
Migraine is the most prevalent neurological disorder (Lipton et al., 2007) and about a third of patients with migraine have attacks with aura (Russell et al., 1995), a usually transient clinical disturbance that can be attributed to brain dysfunction (Goadsby et al., 2002). In migraine with typical aura, the most prevalent aura symptoms are visual disturbances (Russell and Olesen, 1996).
Individuals with migraine visual aura have been documenting the visual percepts of their auras for centuries (Schott, 2007). Lashley was the first to correlate the representation of the visual aura with its likely distribution on the occipital cortex (Lashley, 1941).
The temporal and spatial characteristics of the spread of the migraine visual aura were similar to those of cortical spreading depression (CSD), leading to the hypothesis that CSD is the underlying mechanism of the migraine aura (Leão, 1944).
Based on studies of CSD in animal models, the spread of activity in the occipital cortex underlying the migraine visual aura is commonly represented as a concentrically propagated, expanding wave. However, the pattern of the visual percept of migraine may not necessarily be consistent with this pattern of spread (Dahlem and Hadjikhani, 2009). The specific neuro-anatomical substrates of migraine aura initiation and propagation and their underlying cellular and neurochemical mechanisms remain poorly understood. Careful clinical observation continues to play a key role in expanding our understanding of migraine and its pathophysiology.
Here we present data from a single individual who made consistent and detailed drawings of his migraine visual auras over nearly two decades and created a database of 1000 aura attacks. This database includes detailed maps of his visual perception of hundreds of his migraine auras, noting the precise site of initiation and pattern of spread throughout his visual fields.
These data provide significant new insight into the patterns of visual aura, and suggest mechanisms by which the migraine aura begins and spreads in the visual cortex, and how it is perceived.
Brain. 2013;136(12):3589-3595. © 2013 Oxford University Press