Humans need light for a variety of reasons. Beyond allowing us to perceive our environment with sight, light also activates activity in the brain. A recent study has unexpectedly shown that even individuals who are completely blind are influenced by the presence of light. The presence or absence of light controls many bodily functions, including heart rate, attentiveness, mood, and reflexes. The study will be published in an upcoming edition of Journal of Cognitive Neuroscience. The work is a collaboration between a research team at the University of Montreal and the Brigham and Women’s Hospital in Boston.

The experiment was performed by exposing people who are completely blind to a blue light. The light was turned on and off and the participants were asked whether the light was on or off. The participants were shown to have a non-conscious response to the light, despite not being able to see it. There were more positive identifications made than could be explained by chance alone, though the awareness was non-conscious. This light perception comes from ganglion cells in the retina, which are different from the rod and cone cells that process light for sight.

Next, researchers tested if attentiveness was affected by the presence of light. For this activity, participants had to match sounds with lights on or off. Even though the participants could not visualize the light, they showed an increased attentiveness when light was shining into their eyes.

Finally, the test participants completed a brain scan with functional MRI (fMRI) to measure alertness, memory, and cognition recognition while performing tasks of matching sounds. Across the board, the tasks were completed more efficiently when light was present.

Because of these results, the researchers are speculating that light perception is part of the default mode network. This is the name for the brain activity that occurs non-consciously in the background, while other tasks take priority. They speculate that the ability to perceive light even without actively converting it into images is done to continually pay attention to and monitor the environment. If this is correct, it might help explain why cognitive performance is improved in the presence of light.