Migraine Symptoms: Why Light Increases Migraine Pain

 Approximately 28 million or 12% of the American population suffer from migraines. Unlike common headaches, migraine headaches usually consist of throbbing on one side of the brain. While scientist think they are caused by vasoconstriction, certain triggers can instigate them.

In addition to pain, migraine headaches are often accompanied by nausea, loss of appetite, vomiting, auras, numbness, difficulty speaking, sensitivity to sound, and light-sensitivity. When people suffer from a migraine headache, often they are advised to lay down in a dark bedroom. Although researchers know that light can intensify the pain of migraines, they didn't completely understand why. Approximately, 85% of migraine sufferers have a light-sensitivity. The sensitivity is known as photophobia.

At Beth Israel Deaconess Medical Center (BIDMC), scientists have discovered the visual pathway that triggers migraines in both the sighted and the blind. Apparently, signals transmitted from the retina through the optic nerve can intensify the pain of a migraine.

Researchers divided two blind migraine sufferers into two groups. The first group was unable to see images, sense light, or maintain a normal sleep-wake cycle. However, even though the second group was legally blind and unable to see images, they were able to sense light and maintain normal sleep-wake cycles. While light did not intensify the migraines of the first group, it did intensify the migraines in the second group, especially in the blue or gray wavelengths. Consequently, scientists hypothesized the optic nerve was involved in the intensification of pain since the optic nerve does not carry light signals in a totally blind individual. Furthermore, scientist also believe retinal cells containing melanospin photoreceptors are also involved because they the only functioning light receptors left in legally blind individuals.

After this discovery, scientists tested the theory in a laboratory setting. Using rats with migraines, they injected dyes into their eyes and traced the pathway of the melanospin retinal cells through the optic nerve to the brain, and they found a group of neurons that became electrically active during the migraine. When they inserted electrodes into these neurons, they found the light triggered electrical signals which converged on these cells and increased their acitivity. Even after the light was removed, the neurons remained active.

 Although the study with rats have given scientists a greater understanding of the effects of light on migraines in rats, it may not apply to humans. More research needs to be done yet. However, if it does apply to  humans, one day scientists may be able to develop a way to help migraine sufferers tolerate light rather than laying down in darkened rooms.