By assessing the functional MR images taken during the exercise, the researchers identified 26 human brain regions where activity either decreased or increased in accordance with light-intensity. This luxotonic-related activation occurred across the cerebral cortex, in diverse subcortical structures, and in the cerebellum, encompassing regions with functions related to visual image formation, motor control, cognition and emotion.

They found that light suppressed activity in the prefrontal cortex in proportion to the light intensity. The light-evoked responses in the prefrontal cortex and their alteration by prior light exposure resembled the responses of the intrinsically photosensitive retinal ganglion cells.

Its well-known that changes in ambient lighting that do not necessarily have anything to do with form or object vision influence various basic functions, such as circadian rhythms, visual-reflexes, mood and likely cognitive processing, Sanes said. However, it had remained unclear how these light-intensity signals reached the relevant areas of the human brain.

In this study, the researchers showed that the prefrontal regions of the human brain have light-sensitive signals, and that these signals are similar to intrinsically photosensitive retinal ganglion cells which together, Sanes said, may explain the effects of light intensity on complex emotional and cognitive behaviors.

The findings from our study offer a functional link between light exposure and prefrontal cortex-mediated cognitive and affective responses, Sanes said.

One next logical question to ask, Sanes said, concerns how light affects these same brain pathways and regions in people with mood disorders like seasonal affective disorder or major depressive disorders.

How does that compare to a control group of healthy people not diagnosed with these disorders? he asked. Does light activate the same regions, and if so, are these regions more or less sensitive to light activation? What is the magnitude of difference in the effect? This is an area of ongoing investigation, he said, adding that the answers could inform the development of therapeutic treatments for mood disorders.

Michael Worden from Browns Department of Neuroscience and Carney Institute for Brain Science also contributed to this research, as did researchers from the Hebrew University of Jerusalem.

The research was funded by the National Institutes of Health (R01EY12793, P20GM103645, S10OD025181), an Alcon Research Institute Award, Brown Universitys Division of Biology and Medicine, the National Institute of Psychobiology of Israel, and a Banting Postdoctoral Fellowship of Canada.

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Researchers discover brain pathway that helps to explain light's effect on mood - Brown University