In a new study, Burstein and his colleagues sat sighted volunteers in the throes of a migraine in a dark room and gradually raised the intensity of white, blue, green, amber and then red light. As well as recording how the volunteers said the light affected their pain, Burstein’s team recorded the activity of neurons sending signals from the eye to the brain using a tiny electrode placed on the eyelid. They also measured the volunteers’ brain activity using electrodes placed on their heads.
“We were surprised to see that blue light was no more painful than white or amber or red,” says Burstein. “They were all painful.”
But even more surprising was the finding that low intensities of green light did not increase migraine pain – in fact, it lowered the volunteers’ suffering. “I’ve thought long and hard about it, but I have no idea why green light might be more pleasant,” says Burstein.
The brain and eye recordings taken from volunteers revealed that green light created a smaller amount of electrical activity, both in the eye and the brain, than any other colour of light.
Journal reference: Brain, DOI: 10.1093/brain/aww119