Cerebral Cortex Advance Access originally published online on April 2, 2007
Cerebral Cortex 2007 17(12):2788-2795; doi:10.1093/cercor/bhm007
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Wavelength-Dependent Modulation of Brain Responses to a Working Memory Task by Daytime Light Exposure
1 Cyclotron Research Centre, University of Liège, B-4000 Liège, Belgium, 2 Department of Psychology, Université de Montréal, Montréal, Québec, H3C 3J7, Canada, 3 Surrey Sleep Research Centre, University of Surrey, Guildford, GU2 7XP, UK, 4 Department of Neurology, Centre Hospitalier Universitaire, B-4000, Liège, Belgium
Address correspondence to Pierre Maquet, Centre de Recherches du Cyclotron, Université de Liège, B30, Sart Tilman, B-4000 Liège, Belgium. Email: pmaquet{at}ulg.ac.be.
In addition to classical visual effects, light elicits nonvisual brain responses, which profoundly influence physiology and behavior. These effects are mediated in part by melanopsin-expressing light-sensitive ganglion cells that, in contrast to the classical photopic system that is maximally sensitive to green light (550 nm), is very sensitive to blue light (470–480 nm). At present, there is no evidence that blue light exposure is effective in modulating nonvisual brain activity related to complex cognitive tasks. Using functional magnetic resonance imaging, we show that, while participants perform an auditory working memory task, a short (18 min) daytime exposure to blue (470 nm) or green (550 nm) monochromatic light (3 x 1013 photons/cm2/s) differentially modulates regional brain responses. Blue light typically enhanced brain responses or at least prevented the decline otherwise observed following green light exposure in frontal and parietal cortices implicated in working memory, and in the thalamus involved in the modulation of cognition by arousal. Our results imply that monochromatic light can affect cognitive functions almost instantaneously and suggest that these effects are mediated by a melanopsin-based photoreceptor system.
Key Words: circadian rhythms functional magnetic resonance imaging human cognition light exposure melanopsin
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