Why Light Worsens Migraine Pain

Patient Expert

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How many times have we or the people we know found our Migraines worsened by light? Countless times! Researchers at Beth Israel Deaconess Medical Center in Boston have determined why this happens. This exciting research how visual and pain pathways converge in the brain, causing light to exacerbate the pain of a Migraine.

In an interview, researcher Burstein commented:

"We had no clue in the world where in the world light and pain talk to each other in the brain. They have completely different pathways in the brain...

We identified a new pathway in the brain that originates in the eye and goes to the brain areas where neurons are found that are active during migraine attacks. The light can increase the electrical activity in neurons that are active to begin with."4

The study:

  • Researchers documented the prevalence of Migraine-associated photophobia in 20 (15 female, five male) blind study participants.
  • The demographics of these participants was similar to Migraineurs with normal eyesight for their ages, their age when they experienced their first Migraine attack, frequency of their Migraines, and incidence of visual aura (35% of participants).
  • Six of the participants (group 1) had no light perception because of bilateral enucleation (removal of the eye) or damage to the optic nerves.
  • The remaining 14 participants (group 2) were legally blind, but capable of detecting light.

  • Participants in the first group experience no exacerbation of Migraine pain when exposed to light.

  • Group 2 did experience exacerbation in their Migraine pain when exposed to light, particularly blue or gray wavelenghts.

  • With the findings from these two groups of participants, researchers turned to laboratory animals. They injected dye into the eye and traced the pathway of light sensitive retinal cells through the optic nerve to the brain. There, they found a group of neurons that become electrically active during a Migraine.

  • In the animal model, those neurons remained activated even when the light was removed.

Explanatory comments from Burstein:

"This explains the throbbing headache and accompanying scalp and neck-muscle tenderness experienced by many migraine patients.

Migraine patients may wear sunglasses, even at night... the dimmest of light can make migraine pain worse. Extremely disabling, photophobia prevents patients from such routine activities as reading, writing, working or driving.

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. This suggested to us that the mechanism of photophobia must involve the optic nerve, because in totally blind individuals, the optic nerve does not carry light signals to the brain.

We also suspected that a group of recently discovered retinal cells containing melanopsin photoreceptors [which help control biological functions including sleep and wakefulness] is critically involved in this process, because these are the only functioning light receptors left among patients who are legally blind.

When small electrodes were inserted into these 'migraine neurons,' we discovered that light was triggering a flow of electrical signals that was converging on these very cells. This increased their activity within seconds...

(regarding the neurons remaining activated when light was removed) This helps explain why patients say that their headache intensifies within seconds after exposure to light, and improves 20 to 30 minutes after being in the dark.

Clinically, this research sets the stage for identifying ways to block the pathway so that migraine patients can endure light without pain."2

Summary and comments:

This is very exciting research. As Dr. Burstein commented, now that the pathway responsible foe light exacerbating Migraine pain has been identified, researchers can look for ways to block that pathway and reduce the effects of light on Migraine. Additionally, now that this is understood, it may well lead to understanding our sensitivities to sound and smell.

There is little I can add to what has already been said here. I did, however, ask Dr. Richard Lipton about this research and want to share his comments with you. They summarize this research and it's importance better than I ever could:

This research began with an intriguing question about photophobia; "How is that light worsens pain during a migraine attack?". By evaluating patients who are blind, Burstein and coworkers discovered that in some forms of blindness, migraine pain is worsened by light even in people who can not see. In these patients, a specific population of cells (called RGC or retinal ganglion cells) in the retina are preserved while other cells, responsible for formed vision (rods and cones) are lost. Building on this clinical observation, Burstein discovered a place deep in the brain where input from these RGCs about light conditions and input from the pain pathway converge. Light worsens pain by activating nerve cells at this point of convergence.

These finding are important because:

  1. They make clear that light sensitivity in migraine has a firm anatomic basis. The symptom can be understood.
  2. They help us understand why drugs that relieve the pain of migraine also relieve sensitivity to light.
  3. They may provide a model for helping us understand sound and smell sensitivity as well.3

Resources:

1 Noseda, Rodrigo; Kainz, Vanessa; Jakubowski, Moshe; Gooley, Joshua J.; Saper, Clifford B.; Digre, Kathleen; Burstein, Rami. "A neural mechanism for exacerbation of headaches by light." Nature Neuroscience. Advance Online Publication; January 10, 2010.

2 Press Release. "Study explains why light worsens migraine headaches." Beth Israel Deaconess Medical Center. Boston. January 10, 2010. Via EurekAlert.

3 Interview. Dr. Richard B. Lipton. January 11, 2010.

4 Gardner, Amanda. "Why Light Hurts During Migraine." HealthDay News. January 10, 2010.

Medical review by John Claude Krusz, PhD, MD

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