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"Seeing Without Seeing"

January 19, 2011

An article in the January 19th issue of Nature discussed over ten years of work leading to the discovery and understanding of a third photoreceptor called intrinsically photosensitive retinal ganglion cells (ipRGC's) which use light to synchronize the circadian clock and possibly to influence learning and memory.

The article discusses years of research on mice that found that ipRGC's could use light independently from rods and cones to set the brain's circadian pacemaker and encode information about brightness and patterns of light in daylight conditions, working with rods to help the brain respond to a wide range of brightness levels. The ipRGC's express a gene called Melanopsin that is particularly responsive to blue light and may help to distinguish dawn and dusk without the visual perception of rods and cones.

Steven Lockley, Ph.D studied this receptor in humans and found that exposure to blue light was associated with better learning and attention than exposure to green light. He suggests that further research in this field may find that light can be used to improve health, though more information is needed on the effects of excessive exposure to synthetic light.

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