Gilles Vandewalle is a researcher who studies the regulation of sleep and wakefulness and its importance in cognition and brain health. He typically uses electrophysiology, neuroimaging, and neuropsychological testing to determine the brain mechanisms involved in these things. Two major tools used to address differences in individuals, especially with regard to light impact are genetics and aging.
Vandewalle's research follows various streams: "non-visual impact of light on cognitive brain function, emotion processing and seasonal affective disorder, in young and older individuals; dynamics of basic brain function across the sleep wake cycle; change in sleep wake regulation in aging; link between sleep-wake regulation and Alzheimer disease. "
Vandewalle, G., Schmidt, C., Albouy, G., Sterpenich, V., Darsaud, A., Rauchs, G., ... & Dijk, D. J. (2007). Brain responses to violet, blue, and green monochromatic light exposures in humans: prominent role of blue light and the brainstem. PloS one, 2(11), e1247.
In this study, researchers exposed participants to short duration monochromatic light of varying wavelengths (violet, blue, and green) during a working memory task. At onset of light, blue light (compared to green light) increased activity in the left hippocampus, left thalamus, and right amygdala. During the task, blue light (compared to violet light) also increased activity in the left middle frontal gyrus, left thalamus, and a bilateral area of the brainstem related to the activation of the locus coeruleus. The results support that melanopsin-expressing retinal ganglion cells contribute to brain responses to light during exposure. It also shows the role the brainstem plays in mediating the responses.
This paper seemed to zoom in to a specific aspect of light exposure by looking at more wavelengths of light, including violet.
Vandewalle, G., Balteau, E., Phillips, C., Degueldre, C., Moreau, V., Sterpenich, V., ... & Maquet, P. (2006). Daytime light exposure dynamically enhances brain responses. Current Biology, 16(16), 1616-1621.
In this study, researchers used fMRI to characterize the neural correlates of the alerting effect of daytime light. To do this, they exposed individuals to a short exposure of bright white light, and assessed the responses to an auditory oddball task. Light-induced improvement in alertness was correlated with responses in the posterior thalamus. Light also enhanced responses in cortical areas related to attention and decreased diminutions of activity typically observed during darkness. It was also shown that responses to light declined within minutes after differing region-specific time courses. Their findings suggest that light can modulate activity of subcortical structures related to alertness, promoting cortical activity in networks related to nonvisual cognitive processes. This paper zoomed in to a particular light exposure, in this case, bright white light as opposed to monochromatic light.
Vandewalle, G., Gais, S., Schabus, M., Balteau, E., Carrier, J., Darsaud, A., ... & Maquet, P. (2007). Wavelength-dependent modulation of brain responses to a working memory task by daytime light exposure. Cerebral cortex, 17(12), 2788-2795.
This paper looked at the effects of melanopsin-expressing light-sensitive ganglion cells which are highly sensitive to blue light. Prior, there was no evidence that blue light exposure modulates nonvisual brain activity related to complex cognition. In the study, the researchers use fMRI to show that a short daytime exposure to blue or green monochromatic light differentially modulates regional brain responses during an auditory working memory task. It was shown that blue light usually enhanced brain responses in frontal and parietal cortices as well as the thalamus, while green light typically declined brain responses. The general results of the study are that monochromatic light can affect cognition almost instantaneously and these effects are mediated by a melanopsin-based photoreceptor system. This paper set a general framework to build upon by showing that melanopsin-expressing light-sensitive ganglion cells play a large role in the relationship between light exposure and cognition.