Bright Light May Affect Mood and Learning
We recently discussed how the bright light of our computer monitors and smartphone screens could be keeping us awake longer and causing unnecessary eye strain, but a new study by Johns Hopkins University shows that our love of unnatural lighting may be causing additional harm by causing symptoms found in depression, increasing stress levels and reducing the brain’s ability to learn new information.
The study, published in the journal Nature, was conducted by professor of biology Samer Hattar, who subjected mice to 3.5 hours of light followed by 3.5 hours of darkness for a two-week period. According to Hattar, the mice in the experiment began to exhibit signs of depression as well as increased amounts of cortisol, a stress hormone, and showed difficulty in learning and information retention.
“Of course, you can’t ask mice how they feel, but we did see an increase in depression-like behaviors, including a lack of interest in sugar or pleasure seeking, and the study mice moved around far less during some of the tests we did,” said Hattar. “They also clearly did not learn as quickly, or remember tasks as well. They were not as interested in novel objects as were mice on a regular light-darkness cycle schedule.”
Following the two week period, the mice were treated with an anti-depression drug and saw a return to their normal behavior, suggesting that the problems with learning, stress, and memory were caused by depression.
While the link between how mice and humans interact may seem tenuous to some, Hattar’s supposition does have scientific validity. Mice and humans share a similar type of biological mechanism for processing light by using intrinsically photosensitive retinal ganglion cells (ipRGCs) in our eyes. The brain’s limbic system, which includes structures like the hippocampus and the amygdalae, controls many functions typically affected by depression, such as emotion, behavior, motivation, and long-term memory. Natural rest cycles for the limbic system are governed by the levels of light detected by ipRGCs, leading to lower levels of activity at night as the body prepares for sleep. Unnatural, bright lights therefore cause the limbic system to continue operating when it should instead be slowing down.
“We still don’t know the exact brain regions that are impacted, but we suspect that some regions that are supposed to be settled at night must be activated and disclose some changes in the hormonal levels, specifically in corticosterone. Corticosterone in turn leads to depression and learning deficits,” said Hattar.
While we may not be able to do much to get rid of the fluorescent lights found in most college classrooms, Dr. Hattar does have some additional recommendations for how to keep the limbic system operating correctly at home, primarily through the use of applications that lower the amount of blue light coming from your smartphone or computer screen.
“See how much you can lower the intensity [of the light] so you can still see comfortably, but you are not exposed to incredibly bright light,” says Dr. Hattar. “Get more bright light during the day and limit it at night. It is really actually quite simple. The discovery is quite interesting, but the remedy is quite simple.”