Light is such a potent trigger for migraine that it can intensify an attack within seconds, even in people who are legally blind. Close to 90% of migraineurs have photophobia (light sensitivity), but it was a group of blind migraine sufferers that helped researchers from Beth Deaconess Medical Center in Boston trace the source of a possible problem.

The scientists studied two groups. The first were completely blind and unable to sense light; the second were legally blind but still able to sense light. “While the patients in the first group did not experience any worsening of their headaches from light exposure, the patients in the second group clearly described intensified pain when they were exposed to light, in particular blue or gray wavelengths,” Rami Burstein, PhD wrote in a news release. “This suggested to us that the mechanisms of photophobia must involve the optic nerve, because in totally blind individuals, the optic nerve does not carry light signals to the brain.”

Following the optic nerve, the researchers discovered a group of neurons in the brain that become electrically active when stimulated. These neurons remain activated even when the light is taken away, which explains why the pain of migraine takes longer to abate when migraineurs retreat to a dark place than it does to be aroused.

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