Why Light Makes Migraines Worse...

Scientists have discovered why light makes migraines worse, and the key to the breakthrough was the observation that some blind people also get relief by retreating to somewhere dark.

Rodrigo Noseda and his colleagues at the Beth Israel Deaconess Medical Centre in the US began by asking 20 blind people with migraines whether they experienced light-sensitivity or photophobia when they had headaches.

Surprisingly, some of them did and these were individuals who had sight-loss conditions like retinitis pigmentosa where the light-sensitive rods and cones degenerate, causing visual loss, but the rest of the retina remains healthy. On the other hand, people who were blind owing to congenital absence of their eyes or destruction or removal of the eyes didn't show this light sensitivity.

This suggested to the researchers that signals arising from the retina must be responsible. To find out how, they used dyes injected into rats to label the nerve cells that connect the retina to the rest of the brain.

They found a group of cells that connect to a region called the posterior thalamus. These nerve cells don't carry visual information but instead arise from a special group of retinal cells used by the brain to tell when it is like or dark in order to set the body clock.

But, the team found, the cells in the thalamus to which these nerves were connecting were also activated by pain nerves supplying the meninges, the layers that surround the brain and spinal cord and which are thought to become irritated during migraines and infections like meningitis.

So, by activating the same brain cells as the pain pathway, the light-signalling nerves boost the perception of pain.

Clinically, say the scientists, who have published the work in the journal Nature Neuroscience, this sets the stage for identifying new ways to block the pathway responsible, making migraines slightly less of a headache to endure...