Dim Light May Make us Dumber

Source: Michigan State University

Summary: A groundbreaking research by neuroscientists indicated that Spending too much time in dimly lit rooms and offices may actually change the brain’s structure and hurt one’s ability to remember and learn.

The effects of light on cognitive function have been well-documented in human studies, with brighter illumination improving cognitive performance.  However, the underlying neural mechanisms are not well understood. Researchers from the Michigan State University studied the brains of Nile grass rats (which, like humans, are diurnal and sleep at night) after exposing them to dim and bright light for 4 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 rats 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 4 weeks (after a month-long break), their brain capacity and performance on the task was recovered fully. The study findings were published in the journal Hippocampus.

Bright Light improves illumination

A study by Michigan State University neuroscience researchers (from left) Joel Soler, Lily Yan and Tony Nunez suggests that sustained exposure to dim lights may reduce brain capacity. Credit: Michigan State University

Sustained exposure to dim light led to significant reductions in a substance called brain-derived neurotrophic factor (BDNF), 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. Interestingly, light does not directly affect the hippocampus, meaning it acts first other sites within the brain after passing through the eyes. The research team is 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. One of their 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?

Assoc. Prof. Lily 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?”

More Information: 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 (2017). DOI: 10.1002/hipo.22822


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