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Nov. 3, 2022

MSU psychology research shows daylight has big impact on cognitive functions

Lily Yan and a student

Imagine you are in a laboratory room watching two African grass rats trying to navigate through a maze. One grass rat moves through the course quickly and finds its way out easily. The other struggles and cannot figure out how to get out of the maze. You wonder why one navigates it so easily and the other cannot. You might be surprised to find out that the only factor that changed for each grass rat was light exposure.  

Psychology professor Lily Yan, Ph.D., and her team of researchers are researching with grass rats to understand how light modulates brain functions and behavior. African grass rats are diurnal rodents, so they have similar sleep patterns to humans of sleeping at night and being awake during the day. This allows for much more accurate comparisons between grass rats and humans over the typical lab mice who are not diurnal. 

In her experiment, Yan exposes one group of grass rats to dim light and the other to bright lights to mimic winter and summer light conditions for four weeks. In addition to the maze task, the researchers also study the rats’ brains, specifically the hippocampus which is important for memory; they found nearly 30% reduction in the connectivity of neurons in the hippocampus for the grass rats that are exposed only to dim light. Recent work from graduate student Allison Costello has also found that winter-like dim light conditions lead to increased inflammatory status in the hippocampus and other brain regions involved in regulating mood and cognitive function.  

The grass rats in the dim light group were exposed to 50 lux lighting, similar to the lighting in a typical family room in a house. The grass rats in the bright light conditions were exposed to 1000 lux, similar to the lighting in a department store. The outdoor light level on a cloudless day is roughly 10,000 lux. 

“It’s not a huge difference between the dim and bright light conditions,” said Dr. Yan. “But behaviorally and in the brain, we’ve found significant impacts on cognitive functions.” 

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By: Shelly DeJong