A group of scientists from Michigan State University carried out a study on the link between lighting and brain structure. In conducting the study, the group examined the brains of Nile grass rats after exposing them to dim and bright lights in a span of four weeks. After they conducted the trials, they found that the rats exposed to bright light exhibited significant improvement on a task that they had trained on in the past, which tested their learning and memory capacity. (Related: Use of Bright Lighting May Improve Dementia Symptoms.)
On the other hand, the rats exposed to dim light lost around 30 percent of capacity in the hippocampus and poorly performed on the spatial task. The hippocampus is an important region in the brain that is involved in the learning and memory ability of an individual.
"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 Antonio Nunez, psychology professor and one of the researchers of the study.
But when the dim light-exposed rats were then exposed to bright light for four weeks after a break for one month, they fully restored their brain capacity and exhibited better performance on a spatial task.
Nunez likened the effect to when people cannot find their way back to their cars in a full parking lot after they spent several hours in a mall or movie theater.
Joel Soler, a doctoral graduate in psychology and the lead author of the study, explained that continuous exposure to dim light resulted in significant decrease in brain derived neurotrophic factor, which is a peptide that helps retain healthy connections and neurons in the hippocampus, and in dendritic spines, or the links that enable neurons to communicate with one another.
"Since there are fewer connections being made, this results in diminished learning and memory performance that is dependent upon the hippocampus," Soler said. "In other words, dim lights are producing dimwits."
The scientists also discovered that light does not directly affect the hippocampus. Instead, it acts first other areas within the brain after going through the eyes.
Light affects brain's performance
In a 2014 study published in the journal PNAS, it was discovered that light is important for both visual and “non-visual” functions, such as synchronization of the biological clock to the 24 hour day-night cycle. In addition, light sends a strong stimulating signal for human alertness and cognition and has been frequently employed to improve performance, reversing the negative effect of sleepiness or “winter blues.”
Researchers from the University of Liège involved 16 healthy participants aged 18 to 30 years old. The participants underwent a series of identical function MRI recordings, in which they performed a simple auditory detection task and a harder auditory working memory task, while continuously exposed to the same test light.
“These findings emphasize the importance of light for human cognitive brain functions and constitute compelling evidence in favor of a cognitive role for melanopsin. More generally, the continuous change of light throughout the day also changes us,” the researchers wrote.
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