If you've opted to go for low "mood lighting" in your office, you might want to think again. According to a new study from Michigan State University, when rats are exposed to dim lighting for prolonged periods, their brain capacity diminishes. The same could likely be true for humans.

The rodents used in the study were Nile grass rats, which are diurnal – that means they sleep at night and are active during the day.

When a group of the animals were exposed to dim light during the day for a period of four weeks, they lost about 30 percent of the capacity in their hippocampus, which is a part of the brain associated with learning and memory. They thus performed poorly on a spatial task that they had learned and performed previously.

Another group of rats had been exposed to bright light every day for four weeks, and their performance on that same task improved after that time. Additionally, the performance and brain capacity of the dim-light rats recovered fully, after they were given a break for one month and then subjected to four weeks of bright light.

It was found that sustained exposure to dim light led to a marked reduction in brain derived neurotrophic factor, which is a peptide that maintains healthy connections and neurons in the hippocampus. The dim light also caused a reduction in dendritic spines, which are the connections that allow neurons to communicate with one another.

Because light doesn't affect the hippocampus directly, the scientists believe that it must first be acting on other parts of the brain, after passing through the eyes. One area that's a possibility is a group of neurons within the hypothalamus, which produce a peptide known as orexin. That peptide, in turn, is known to influence a variety of brain functions.

Given this fact, the researchers wonder if giving orexin to the dim-light rats would have the same affect as exposing them to bright light. If it does, then it could have implications for people such as the elderly, or those who have eye problems.

"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?" asks Lily Yan, who worked on the project along with Antonio "Tony" Nunez and Joel Soler. "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?".