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Marjorie Bekaert Thomas
Advances in health and medicine.
General Health Channel
Reported November 16, 2012

Let There (NOT) Be Light!


(Ivanhoe Broadcast News) – Late nights on the computer or sleeping with the TV on can have serious repercussions for mental health. Since technology has taken over it is normal for people to stay up late working, playing and socializing, but that modern lifestyle may come at a cost, according to a new study.
The study, led by a Johns Hopkins biologist, showed that prolonged exposure to bright light at night, even that of lamps, computers and iPads may be having a negative effect on mood and ability to learn. The study was conducted on mice and found that light exposure caused symptoms of depression and decreased memory and task learning.
“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, elevates levels of a certain stress hormone in the body, which results in depression and lowers cognitive function,” said Samer Hattar, a biology professor in the Johns Hopkins University’s Krieger School of Arts and Sciences.
The light activated special cells in the mice’s eyes called intrinsically photosensitive retinal ganglion cells, or ipRGCs. This affected the brain’s center for mood, memory and learning.
“Mice and humans are actually very much alike,” Hattar said. “They have these ipRGCs in their eyes which affect them the same way. In this study we make reference to previous studies on humans, which show that light does indeed impact the human brain’s limbic system. The same pathways are in place in mice.”
Shorter days in the winter cause some people to develop seasonal affective disorder, a form of depression. Some patients with this mood disorder benefit from light therapy, which is regular exposure to bright light. Hattar’s team thought mice would react the same way.
The theory was tested by exposing the animals to a cycle of 3.5 hours of light followed by 3.5 hours of darkness. Previous studies using this cycle found that it did not disrupt sleep cycles, but Hattar found that it did cause the mice to develop depression-like symptoms.
They saw an increased lack of interest in sugar or pleasure seeking,  less movement and the mice did not learn as quickly or remember tasks as well, said Hatter. There were also increase levels of cortisol, a stress hormone that has been linked to learning issues.
“They were not as interested in novel objects as were mice on a regular light-darkness cycle schedule,” he said.
After the mice were treated with Prozac, their previous moods and levels of learning were restored.
 “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,” Hattar said. “Only use what you need to see.”
Using less-intense lighting at night will most likely not cause the ipRGCs to activate, he said, allowing humans to continue their night life.
Source: Nature, November 14th
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