Evidence indicating that pre-migraine CSD can begin in either V1 or V2, and cross a border into the other

Abstract

The visual aura that often precedes migraine has been generally accepted as due to Cortical Spreading Depression, or CSD, and previously thought to be limited to V1. The author has precisely documented over 350 aura episodes over 10 years, which have revealed repeating origin locations and patterns. First, a scintillating “fortification” scotoma (assumed due to crossing of orientation columns) indicates “brushfire” coverage of most of V1, although some smaller areas have never been crossed, and one small area doubles back. Second, when a later episode begins at the same visual (or cortical) origin, they have identical progression patterns, even if observed years apart, indicating a fixed relationship to topography of the calcarine sulcus. Also, there have been more subtle observations of auxiliary negative scotoma without scintillations, indicating a V2 location. As either type of scotoma progression approaches the visual vertical meridian, it appears to “bounce” back from the meridian, while it changes from one scotoma mode to the other. This seems to be visual evidence of the CSD crossing the V1/V2 borders between striate and non-striate cortex, or from V2v through V1 to V2d.