Why does a migraine aura drift slowly across the visual field? · Grey Matter

The visual cortex is a map: neighbouring points of the visual field are handled by neighbouring patches of cortex.

Why does a migraine aura drift slowly across the visual field?

The visual cortex is a map: neighbouring points of the visual field are handled by neighbouring patches of cortex. A wave of spreading depression crossing that map at about 3 mm per minute therefore produces a disturbance that crosses the visual field in the same order, a flickering edge (the wave front) followed by a blind patch (the depressed tissue behind it). Charting his own auras, Lashley estimated in 1941 that the underlying process moved at about 3 mm per minute, and functional MRI in 2001 showed a change in the occipital cortex advancing at about 3.5 mm per minute in step with a subject's aura.