Light Helps Promote Brain Activity—Even In Blind People

By Joelle Renstrom | Published

Photoreceptive ganglion
Photoreceptive ganglion

Researchers at the Boston Brigham and Women’s Hospital and University of Montreal recently published a study in the Journal of Cognitive Neuroscience detailing their findings about how light affects cognition. The most surprising aspect of their experiment is not just that light can promote brain activity, especially when someone is working on a cognitive task, but that this happens even in people who are totally blind.

Light does a lot more than help us see. It gives our brain important situational and environmental information, primarily by indicating whether it’s night or day. You might think that our brains wouldn’t really care about that so much when it comes to performance — I enjoy writing in the dark, for example — but it actually matters a lot. Our biology, behavior, and metabolism take signals from the environment. When you get up in the morning, the first light you switch on often has a jarring effect — the light is what wakes you up, but not simply because it’s bright. It also stimulates responses and activities that humans generally associate with daytime functioning, such as alertness and mood, as well as increased focus and better performance on tasks.

When we look at objects, our eyes use rods and cones to see. But as these researchers discovered, our brains don’t use the same method for “seeing” light. We actually detect light with the help of a photoreceptor in the retina’s ganglion cell layer. But here’s the really interesting part — those photoreceptors can promote visual functioning in the brain even if the retinal cells can’t absorb or process light. If you’re skeptical, consider this: scientists verified the results on three completely blind people.

blue light

The three participants were shown a blue light (which they couldn’t see, I’ll remind you) and then the scientists asked them whether the light was off or on. Even though they couldn’t see the light, they still were able to correctly indicate whether it was on or off. The next phase of the study involved monitoring the subjects’ brain activity when they were listening to a sound and seeing how their brain activity changed when the lights were flashed. Because their brains were already attentive to the sound information, the scientists wanted to see if the flashing light would have any impact on the brain patterns — it did.

The last phase involved an MRI brain scan while participants completed a sound-related task, during which the scientists continued to flash the lights in their eyes. The MRI showed that, within a minute of seeing blue light, regions of their brains that helped them complete the sound-related task, such as alertness and cognition regulation, were activated. The scientists believe that if we’re not immediately engaged in a task, we use the minimal number of resources available to process environmental information. Light, however, appears to be crucial to maintaining attention and high cognitive functioning, and is detectable via a more fundamental process than what we’d traditionally regard as sight. Pretty interesting, and may explain a lot about Gremlins.