According to a new study published in the journal Hippocampus, spending too much time in dimly-lit environment may change the brain’s structure and hurt our ability to remember and learn.
African grass rats (Arvicanthis niloticus) exposed to dim lights (DLD) for four weeks experienced, on average, a 30% decrease in the number of ‘dendritic spine’ connections in their brains, which are the tiny protrusions near the solid green line, a dendrite. These rats performed poorly on a maze-like task. Rats exposed to bright light (BLD), on the other hand, had many more of the dendritic connections and showed superior performance on the task. Image credit: Michigan State University.
A team of Michigan State University researchers, led by Dr. Lily Yan, studied the brains of diurnal African grass rats (Arvicanthis niloticus) after exposing them to dim and bright light for four weeks.
The rodents exposed to dim light lost about 30% of capacity in the hippocampus, a critical brain region for learning and memory, and performed poorly on a spatial task they had trained on previously.
The animals exposed to bright light, on the other hand, showed significant improvement on the spatial task.
Further, when the rodents that had been exposed to dim light were then exposed to bright light for four weeks (after a month-long break), their brain capacity and performance on the task recovered fully.
“When we exposed the rats to dim light, mimicking the cloudy days of Midwestern winters or typical indoor lighting, the animals showed impairments in spatial learning,” said co-author Professor Antonio ‘Tony’ Nunez.
“This is similar to when people can’t find their way back to their cars in a busy parking lot after spending a few hours in a shopping mall or movie theater.”
“Sustained exposure to dim light led to significant reductions in a substance called brain derived neurotrophic factor — a peptide that helps maintain healthy connections and neurons in the hippocampus — and in dendritic spines, or the connections that allow neurons to ‘talk’ to one another.”
“Since there are fewer connections being made, this results in diminished learning and memory performance that is dependent upon the hippocampus. In other words, dim lights are producing dimwits.”
Interestingly, light does not directly affect the hippocampus, meaning it acts first other sites within the brain after passing through the eyes.
“We’re investigating one potential site in the rodents’ brains — a group of neurons in the hypothalamus that produce a peptide called orexin that’s known to influence a variety of brain functions,” Dr. Yan said.
“One of our major research questions: If orexin is given to the rats that are exposed to dim light, will their brains recover without being re-exposed to bright light?”
The project could have implications for the elderly and people with glaucoma, retinal degeneration or cognitive impairments.
Dr. Yan said: “for people with eye disease who don’t receive much light, can we directly manipulate this group of neurons in the brain, bypassing the eye, and provide them with the same benefits of bright light exposure?”
“Another possibility is improving the cognitive function in the aging population and those with neurological disorders. Can we help them recover from the impairment or prevent further decline?”
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Joel E. Soler et al. Light modulates hippocampal function and spatial learning in a diurnal rodent species: A study using male Nile grass rat (Arvicanthis niloticus). Hippocampus, published online December 27, 2017; doi: 10.1002/hipo.22822
