One of the most fascinating things about migraine is the symptom known as aura. More specifically, visual disturbances that sometimes are a part of a migraine attack. Some people have had visual disturbances and no headache at all, though most tend to have the headache and not the visual aura.
About 15% of migraineurs have some kind of aura. They see zig zags, or have a partial lack of vision, or see flashing lights, for example. But why does this happen?
We do know that as a migraine attack progresses, there is a spreading change in the brain – an area where there is a suppression of activity, surrounded by an area with hyperactivity. It’s likely that, as this change spreads over the visual cortex, the instability of the neuron-firing causes the visual hallucinations. Because the effect is spreading, the hallucinations usually change, and eventually disappear. For the migrainuer they may be in one eye, they may be partial or quite detailed, and they can be different as the minutes pass.
But why the weird shapes?
In 1926, psychologist Heinrich Klüver studied the hallucinations that came from patients taking mescaline, a psychedelic alkaloid. He found that there were four patterns that people tended to see, called form constants. The four were tunnels, spirals, cobwebs and lattices (ie checker boards and triangles). These four geometric patterns tend to appear with certain drugs or conditions such as epilepsy and migraine.
So where do these patterns come from? Are you just imagining shapes? Is it something in your body that you’re seeing?
Professor of Mathematics at the University of Utah Paul Bressloff did extensive calculations which seemed to point back to the visual cortex. It looks like the things you see actually reflect how the visual cortex works – how it’s set up. When the neuron-firing gets destabilized for whatever reason, predictable patterns are seen by your brain. It’s like seeing part of a map of your visual cortex. A summary of Bressloff’s findings are here (if you want to go in-depth, read one of his papers, available here in pdf format).
Visual auras in migraine are usually not too serious, but they can become incapacitating for some people. Migraine medication can help to minimize the symptoms if need be.
Thanks to Mind Hacks for pointing to Bressloff’s research.