November 15, 2012
Prolonged Bright Light During Night Hours Affects Mood And Learning Ability
[ Watch the Video: Light Exposure Leads To Depression, Learning Issues ]
Connie K. Ho for redOrbit.com — Your Universe Online
The team of investigators showed how special cells in the eye, otherwise known as photosensitive retinal ganglion cells (ipRGCs), were stimulated by bright light. When the cells were activated, they would influence the brain´s center for learning, memory and mood. A group of mice were utilized in the study, and the results could be applied to humans as well.
"Basically, what we found is that chronic exposure to bright light -- even the kind of light you experience in your own living room at home or in the workplace at night if you are a shift worker -- elevates levels of a certain stress hormone in the body, which results in depression and lowers cognitive function," remarked Samer Hattar, a biology professor in the Johns Hopkins University's Krieger School of Arts and Sciences, in a prepared statement.
The researchers highlighted how the results of the study could correlate with “seasonal affective disorder,” a type of depression found in areas where winter has shorter days and there are days with less sunlight. In particular, patients with this type of depression could reap positive results from a treatment that allowed for regular exposure to bright light — otherwise known as “light therapy.”
"Mice and humans are actually very much alike in many ways, and one is that they have these ipRGCs in their eyes, which affect them the same way," continued Hattar in the statement. "In addition, in this study, we make reference to previous studies on humans, which show that light does, indeed, impact the human brain's limbic system. And the same pathways are in place in mice."
It was theorized that the mice in the study would respond to light therapy similarly to humans. They experimented the theory by providing the mice with 3.5 hours of light and then 3.5 hours of darkness. While the cycle of light versus dark did not affect the sleeping schedule of the mice, the researchers saw that the mice exhibited depression-like behaviors. In particular, the mice displayed higher levels of cortisol, a stress hormone that is related to learning issues. When the mice were treated using the anti-depressant Prozac, there were less depression-like symptoms and the mice reverted to healthier moods.
"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," noted Hattar in the statement. "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."
Based on the results of the study, the researchers encourage humans to be aware of the effects that prolonged, regular exposure to bright light during night hours can have as it can impact people´s learning ability and mood.
"I'm not saying we have to sit in complete darkness at night, but I do recommend that we should switch on fewer lamps, and stick to less-intense light bulbs: Basically, only use what you need to see. That won't likely be enough to activate those ipRGCs that affect mood," concluded Hattar in the statement.
The findings of the study were recently published in the journal Nature.