“Although photophobia is not usually as incapacitating as headache pain itself, the inability to endure light can be disabling,” said Rami Burstein, the HMS John Hedley-Whyte Professor of Anaesthesia at Beth Israel Deaconess and lead author of the study.
“More than 80 percent of migraine attacks are associated with and exacerbated by light sensitivity, leading many migraine sufferers to seek the comfort of darkness and isolate themselves from work, family and everyday activities,” said Burstein, who is vice chair of research in the Department of Anesthesia, Critical Care and Pain Medicine and academic director of the Comprehensive Headache Center at Beth Israel Deaconess.
Five years ago, Burstein and colleagues made the surprising discovery that blue light hurts migraine patients who are blind. This finding prompted the idea that abnormal sensitivity to light during migraine could be alleviated by blocking blue light.
Because that earlier study involved only blind patients who could not detect all colors of light, Burstein and his colleagues devised a way to study the effects of different colors of light on headache in patients without visual impairment.
In the current study, Burstein and colleagues found that of all light to which migraine sufferers are exposed, a narrow band of green light worsens migraine significantly less than all other colors of light and that at low intensities green light can even reduce headache pain. Of 69 participants, 41 completed the study.
The researchers asked patients experiencing acute migraine attacks to report any change in headache when exposed to different intensities of blue, green, amber and red light.
At high intensity of light—as in a well-lit office—nearly 80 percent of patients reported intensification of headache with exposure to all colors but green. Unexpectedly, the researchers found that green light even reduced pain by about 20 percent.
To understand exactly why green light causes less pain to patients with migraines, Burstein and colleagues designed experiments in which they measured the magnitude of the electrical signals generated by the retina (in the eye) and the cortex (in the brain) of these patients in response to each color of light. They found that blue and red lights generated the largest signals in both the retina and the cortex and that green light generated the smallest signals.
Next, applying techniques recently developed by Rodrigo Noseda, HMS assistant professor of anaesthesia at Beth Israel Deaconess, they used animal models of migraine to study neurons in the thalamus, an area of the brain that transmits information about light from the eye to the cortex. These neurons were found to be most responsive to blue light and least responsive to green light, explaining why the migraine brain responds favorably to green light.
“These findings offer real hope to patients with migraines and a promising path forward for researchers and clinicians,” said Burstein.
Burstein is now working to develop a more affordable light bulb that emits “pure” (narrow-band wavelength) green light at low intensity, as well as affordable sunglasses that block all but this narrow band of pure green light.
Currently, the cost of one such light bulb is prohibitively high, and the technology to block all but pure green light in sunglasses is available only in light microscopy, which is also very costly.
About this psychology research article
Funding: This study was supported by National Institutes of Health grants R37 NS079678 and RO1 NS069847.
Source: Jennifer Kritz – Harvard Image Source: This NeuroscienceNews.com image is adapted from the Harvard press release. Original Research:Abstract for “Migraine photophobia originating in cone-driven retinal pathways” by Rodrigo Noseda, Carolyn A. Bernstein, Rony-Reuven Nir, Alice J. Lee, Anne B. Fulton, Suzanne M. Bertisch, Alexandra Hovaguimian, Dean M. Cestari, Rodrigo Saavedra-Walker, David Borsook, Bruce L. Doran, Catherine Buettner, and Rami Burstein in Brain. Published online May 17 2016 doi:10.1093/brain/aww119
Cite This NeuroscienceNews.com Article
[cbtabs][cbtab title=”MLA”]Harvard. “Exposure to Narrow Band of Green Light Improves Migraine Symptoms.” NeuroscienceNews. NeuroscienceNews, 17 May 2016. <https://neurosciencenews.com/migraine-green-light-4247/>.[/cbtab][cbtab title=”APA”]Harvard. (2016, May 17). Exposure to Narrow Band of Green Light Improves Migraine Symptoms. NeuroscienceNews. Retrieved May 17, 2016 from https://neurosciencenews.com/migraine-green-light-4247/[/cbtab][cbtab title=”Chicago”]Harvard. “Exposure to Narrow Band of Green Light Improves Migraine Symptoms.” https://neurosciencenews.com/migraine-green-light-4247/ (accessed May 17, 2016).[/cbtab][/cbtabs]
Migraine photophobia originating in cone-driven retinal pathways
Migraine headache is uniquely exacerbated by light. Using psychophysical assessments in patients with normal eyesight we found that green light exacerbates migraine headache significantly less than white, blue, amber or red lights. To delineate mechanisms, we used electroretinography and visual evoked potential recording in patients, and multi-unit recording of dura- and light-sensitive thalamic neurons in rats to show that green activates cone-driven retinal pathways to a lesser extent than white, blue and red; that thalamic neurons are most responsive to blue and least responsive to green; and that cortical responses to green are significantly smaller than those generated by blue, amber and red lights. These findings suggest that patients’ experience with colour and migraine photophobia could originate in cone-driven retinal pathways, fine-tuned in relay thalamic neurons outside the main visual pathway, and preserved by the cortex. Additionally, the findings provide substrate for the soothing effects of green light.
“Migraine photophobia originating in cone-driven retinal pathways” by Rodrigo Noseda, Carolyn A. Bernstein, Rony-Reuven Nir, Alice J. Lee, Anne B. Fulton, Suzanne M. Bertisch, Alexandra Hovaguimian, Dean M. Cestari, Rodrigo Saavedra-Walker, David Borsook, Bruce L. Doran, Catherine Buettner, and Rami Burstein in Brain. Published online May 17 2016 doi:10.1093/brain/aww119