Light Activates the Human Brain, Even in the Blind

Light may be more important to the human brain than you might have thought--even when it comes to someone who is completely blind. Scientists have discovered that light enhances brain activity during a cognitive task, even for those who can't see. The findings reveal further insight into the brain and how quickly light impacts cognition.

"Light doesn't just allow us to see, it tells the brain whether it's night or day which in turn, ensures that our physiology, metabolism and behavior are synchronized with environmental time," said Steven Lockley, one of the researchers, in a news release.

For diurnal species, like humans, light stimulates day-light brain activity. This can enhance alertness, mood and performance on many cognitive tasks.  Yet for those that are blind, one would assume that these light signals wouldn't reach the brain. It turns out that this isn't the case, though. Researchers have discovered a novel photoreceptor in the ganglion cell layer of the retina, different from the rods and cones we use to see.

In this latest study, researchers wanted to test if these specialized photoreceptors in the retina also contributed to visual function in the brain even when cells in the retina responsible for normal image formation have lose their ability to receive or process light. The scientists asked three participants to say whether a blue light was on or off, even though they could not see the light and were blind. Surprisingly, the researchers found that the volunteers did have a non-conscious awareness of the light; in fact, they were able to determine when the light was on greater than chance without being able to see it.

The researchers then look at look at what happened to brain activation when light was flashed at their eyes at the same time as their attentiveness to a sound was monitored. This allowed the scientists to determine whether the light affected brain patterns associated with attentiveness. In the end, they found out that it did.

In a final test, the volunteers had their brains scanned with a functional MRI brain scan. During the scan, they performed a simple sound matching task while lights were flashed in their eyes.

"The fMRI further showed that during an auditory working memory task, less than a minute of blue light activated brain regions important to perform the task," said Gilles Vandewalle, one of the researchers, in a news release. "These regions are involved in alertness and cognition regulation as well being as key areas of the default mode network."

The findings reveal a little bit more about how light plays a role in the function of the human brain. More specifically, it reveals that it can also impact those who are blind and explains the brain's performance during certain tasks.

The findings are published in the Journal of Cognitive Neuroscience.