We can detect light even if we cannot see it. And in a startling new discovery, even some totally blind people can detect light. Brief exposure to blue light triggered brain activity associated with alertness and attention – helping scientists further understand light’s role in cognition for all people.
“The eye plays a dual role in mammalian physiology,” says Olivier Collignon of the Center for Mind/Brain Science at the University of Trento in Italy. “In addition to detecting light to help us see, the eye also detects light for regulation of multiple ‘non-image-forming’ responses in humans.” For example, light helps us to distinguish day from night, thus influencing our circadian rhythms, metabolism, and behavior.
When Collignon was a postdoctoral student at the University of Montreal studying how visual regions reorganize in the brain in blind people, he became intrigued by “non-image-forming” photoreceptors – cells in the retina, separate from the rod-and-cone system, that enable light detection without the person consciously seeing it. Collignon signed on with colleague Gilles Vandewalle who was working with his adviser Julie Carrier and collaborator Steven Lockley of Harvard to study whether they could test how these special photoreceptors work by looking at totally blind individuals.
Finding blind individuals with non-image-forming photoreceptors for the experiment was challenging, but it offered a unique opportunity to investigate light in the absence of conscious vision. The participants were three of only nine identified worldwide that Lockley’s research group had previously identified as retaining specific light-induced processes. “All three participants had been declared totally blind for at least 10 years, but the cause and duration of sight loss differed,” Collignon says. The three blind individuals flew to Montreal and underwent intense testing for several days. “We were lucky to work with extremely dedicated volunteers showing inexhaustible patience during our tests,” Collignon says.
The researchers first asked the participants to choose whether a blue light was on or off. Past research had shown that blue light is especially effective at inducing neural responses. They then used electroencephalography (EEG) to see whether up to 2 seconds of exposure to high-intensity blue light could modify brain activity while the participants performed an auditory detection task. Finally, they had participants perform an auditory working-memory task and then exposed them to less than a minute of blue light while the participants were in an fMRI scanner.
“By using a plurality of methods, we wanted to take the advantages of the strength of each of them to converge toward a more comprehensive understanding of the mechanisms underlying ‘non-image-forming’ vision,” Collignon says. In each case, the patients were able to detect the blue light, and the researchers found distinct brain activity associated with higher cognitive functions, as published in the Journal of Cognitive Neuroscience.
“The rapidity of light impact on brain activity was surprising – the administration of as little as 2 seconds of high-intensity blue light was able to modulate brain activity,” Collignon says, “but only when the brain was actively processing the acoustic stimulation.” The results show several key findings about non-image-forming photoreceptors for all people: first, that they can rapidly enhance brain activity when a person is actively processing information; second, that they play a critical role in cognition and sleep-wake regulation; third, that they affect a fundamental aspect of brain network organization.
Indeed, the fMRI results specifically showed that brief exposure to the blue light triggered the recruitment of supplemental prefrontal and thalamic brain regions involved in alertness and cognition regulation, as well as key areas of the default-mode network. The default network is important in helping us maintain attention when we are not actively engaged in an activity, thus putatively implicating light’s role in attention.
“These unique data confirm and extend the discovery of a novel non-rod, non-cone blue light photoreceptor in the mammalian eye and show that light plays an important role in brain function,” Collignon says. The next step, he says, is to identify more blind individuals to test. “Given the limited sample of three participants – although they represent one-third of the population of such individuals identified to date – our EEG and fMRI results have to be considered as a ‘proof of concept,’ rather than a fine-grained identification of the brain mechanisms involved in the non- image-forming impact of light on cognition.”
-Lisa M.P. Munoz
The paper, “Blue Light Stimulates Cognitive Brain Activity in Visually Blind Individuals,” Gilles Vandewalle, Olivier Collignon, Joseph T. Hull, Véronique Daneault, Geneviève Albouy, Franco Lepore, Christophe Phillips, Julien Doyon, Charles A. Czeisler, Marie Dumont, Steven W. Lockley, and Julie Carrier, was published in the December 2013 Journal of Cognitive Neuroscience
Media contact: Lisa M.P. Munoz, CNS Public Information Officer, email@example.com