Research Finding Tells Reason for Migraine Sensitivity to Light

Now we cannot dismiss the complaint of migraine sufferers by simply saying that they whine about light hurting during their headache. A research finding has stated reasons about why light exacerbates the already debilitating pain of migraines, even in some blind people. A recent online report published in Nature Neuroscience reveals how visual and pain pathways in the brain converge to produce this phenomenon.

The research findings are unlikely to help migraine patients in the near future by improving the anti migraine drugs. However, according to Dr. Michael Palm, "this gives us a little better insight as to the theory and mechanism behind migraine." Dr. Palm is an assistant professor of neuroscience and experimental therapeutics and internal medicine at Texas A&M Health Science Center College of Medicine, College Station, and director of the Parkinson's and Headache programs at Texas Brain and Spine Institute in Bryan.

The reason cited for migraine sensitivity to light says that there are cells in a part of the brain called the thalamus where information from the visual system and information from the pain system converge. This anatomic convergence leads to light making head pain worse. Thalamus is the brain's sensory switchboard that receives sensory signals from different parts of the body and then redirects them to various sensory, motor and cognitive areas of the cortex.

Based on one of the major migraine symptoms- photophobia- the researchers designed their strategy for studying migraine sensitivity to light. About 85 to 90% of all migraine sufferers report having photophobia, which is when light makes the pain worse. The research team studied 20 blind individuals who suffered from migraines. Six of these participants had no light perception at all and no functioning optic nerve. These individuals did not experience any photophobia. The rest of the 14 people could sense light and dark and also experienced photophobia. This made the researchers understand that the optic nerve is critically needed to produce photophobia or exacerbation of the headache by light.

The next discovery of these researchers was that a set of photoreceptors called melanopsin project onto neurons on the thalamus that also process pain signals. At this stage they needed to follow in the brain the pathways that lead from the eye into the brain using the third group of photoreceptors. As such, they shifted to animals for their further study. In their attempt to find why light hurts during migraine, the reasearchers 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. Now they knew that light can increase the electrical activity in neurons that are active to begin with. This provides an anatomic and physiological basis for a common experience felt by all migraine sufferers. Light hurts during migraine because there is an anatomic pathway that links the visual system to the pathway that produces head pain.

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