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T. A. LeGates, C. M. Altimus, S. Yang, T. Weber, A. Kirkwood, S. Hattar; Light Information Influences Cognitive Functions via Intrinsically Photosensitive Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):677.
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Many physiological and behavioral functions vary over the course of a day, such as hormone secretion and the sleep/wake cycle. The precise timing of these rhythmic outputs depends on synchronization to the solar day. While the introduction of artificial lighting enables people to utilize more hours of the day, the presence of light at night consequently disrupts light-dependent rhythms. Recent work has shown that light can directly influence the limbic system mediating functions such as alertness, working memory, and mood. In addition, exposure to light at the wrong time of day negatively impacts human health.
To gain a better understanding of how light information influences limbic functions, we housed mice in a light paradigm that provided exposure to light pulses throughout the circadian cycle and then assessed learning and mood related behaviors. In this light cycle, mice experience light at the wrong time of the day while circadian rhythms remain intact and sleep unchanged. In mammals, light is transduced by photoreceptors in the retina into an electrical signal that can be interpreted by the brain. To determine the cells responsible for conveying this light information to areas of the brain that control learning and mood, we used a mouse line lacking melanopsin containing intrinsically photosensitive retinal ganglion cells (ipRGCs). These ipRGCs have been shown to convey light information to modulate circadian rhythms and sleep but have not been linked to light-influenced limbic functions.
We show that animals exposed to the light paradigm described above have defects in learning as well as increased anxiety- and depression-related behaviors. Mice lacking ipRGCs are unaffected by this light cycle.
These findings establish that disruptive light conditions can negatively impact limbic functions in particular learning and mood and set up a new role for ipRGCs within the function of the limbic system.
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