New research could explain why light worsens migraine

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Posted 11/01/10

New research published in Nature Neuroscience suggests that scientists at Beth Irsrael Deaconess Medical Center (BIDMC) have identified a new pathway that underlies sensitivity to light during migraine in both blind individuals and in individuals with normal eyesight.

Many migraineurs are extremely sensitive to light, a condition known as photophobia, which can prevent them from continuing with normal daily activities.

It was the observation that even blind individuals who suffer from migraines were experiencing photophobia that led respected study authors, Ramai Burstein, PhD and Rodrigo Noseda PhD to hypothesize that signals transmitted from the retina via the optic nerve were somehow triggering the intensification of pain.

The study looked at two groups of blind individuals who suffered migraine headache. Patients in the first group were totally blind (unable to see images or to sense light) and in the second group people were classified as legally blind but could detect the presence of light.

Researchers found that those in the first group did not experience any worsening of their headaches from light exposure, but in the second group pain intensified when they were exposed to light, in particular blue or grey wavelengths.

Researchers suggest that the mechanism of photophobia must involve the optical 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."

In the study the researchers found that they could trace the path of the melanopsin retinal cells through the optic nerve into the brain, where they found a group of neurons that become electrically active during migraine.

Burstein says: "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."

He noted that even when light was removed, these neurons remained activated.  "This helps explain why patients say their headache intensifies within seconds after exposure to light, and improves 20 to 30 minutes after being in the dark."

The discovery of this pathway provides scientists with a new avenue to follow in working to address the problems of photophobia and identifying ways to block the pathway so that migraine patients can endure light without pain.

Migraine Action asked members of its Medical Advisory Board to comment on the new research.

Dr Andrew Dowson, Chairman of Migraine Action's Medical Advisory Board and Director of Headache Services at King's College Hospital, London comments:

"My own research of several years ago identified that migraineurs were more sensitive to light within and outside of migraine attacks. Furthermore the red and blue ends of the spectrum were both implicated (rather than the green middle of the spectrum). The paper confirms that light exacerbates the pain within a migraine attack. It goes on to suggest that this is due to a non-image forming retinal pathway, that has not been suggested before. It is interesting to see an explanation for part of the previously observed symptomatology. This new pathway will probably lead to new targets for treatment of migraine, especially in those with photophobia (not all migraineurs report this symptom). This is potentially another piece of the migraine jigsaw and at this stage it is not clear how it will impact on our overall understanding and enhance treatment. It is true to say, however, that the more pieces we have of the jigsaw, ultimately the better the chance of helping sufferers."

Dr Sue Lipscombe, a GP from Brighton with a specialist interest in headache commented:

"It is interesting as it suggests that an external source is contributing to the migraine condition and it is not just a contained brain disorder that just takes its cycle but that there are outside modifying factors. These findings suggests that more research is necessary in this area and may help to modify patient's suffering."

Dr Brendan Davies at North Midlands Regional Headache Clinic adds: "This is potentially very important both to explain the mechanism of a common symptom in migraine and other primary and secondary headache syndromes and especially if we can identify which central brain areas this retinal pathway projects to  and what brain neurotransmitters are expressed there as potentially it could open up another new target for any treatments".

Clifford Lomas, Osteopath comments; "Migraine mainly affects the opthalmic branch of the trigeminal nerve which is in close proximity to the optic nerve so I suppose there is overlap of sensitivity."

Lee Tomkins, Director of Migraine Action, says: I think everyone with migraine will have experienced light sensitivity at some time, and this is very interesting research that now gives some clues as to the physical processes that might be causing this symptom. We have known from previous research that this sensitivity can be triggered by the blue light waves in the light spectrum, but avoiding grey light is a new aspect, and we are now wondering if this research might help us to further understand why so many migraineurs are sensitive to low energy light sources as well."

To read the BBC Online News feature on this story click here

To read information about the reseach on the NHS Choices website click here

The story has also been featured on BBC Radio 2 and BBC Radio Scotland.

For journalists who are interested in interviewing Ms Lee Tomkins, Director of Migraine Action, or members of the charity's medical advisory board, please call Rachel Markham on 0116 275 8317 or email rachelmarkham@migraine.org.uk

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