The day after Christmas, at around noon, I saw my first one of these.
It's called a scintillating scotoma, and it precedes classic migraines, developing from the center of the visual field outwards over the course of several minutes. A more general term used for the visual effect is a "migraine aura".
I saw the edges of the scotoma, drawn in hash marks above, as green and yellow sparkling lights on a dark field, pulsating and well...scintillating.
It's thought that the visual disturbance is caused by a seizure-like event in the occipital lobe, where vision is perceived. The cells become strongly electrically excited, and that soon exhausts the neurons by altering the ionic balance between extracellular and intracellular space. This results in cellular depression.
Probably, the sparkly, scintillating part of the visual effect is caused by the excited cells, a wave that spreads and grows, and the dark part left in the center are the cells that have become exhausted and depressed. It's really cool that we can actually see that when it happens in the visual cortex.
For me, the visual effect happened only on the right side of my field of vision, which means it was the left hemisphere of my occipital lobe that was experiencing this "spreading depression", as it is called.
Luckily, the headache that came after was mainly in my left temple, and was pretty mild compared to my initial fears. I took some ibuprofen as soon as I figured out what the heck was going on, and massaged the acupressure point in my left eyebrow, which was very tender.
As neat as it was to physically see a cortical event that did not corresponded to any outside sensory stimulus, I hope I never see it again.
As neat as it was to physically see a cortical event that did not corresponded to any outside sensory stimulus, I hope I never see it again.
