First they said it was the lack of light in winter. Now they think it might be caused by too much light.
The scientists knew that shorter days in the winter cause some people to develop a form of depression known as "seasonal affective disorder" and that some patients with this mood disorder benefit from "light therapy," which is simple, regular exposure to bright light.
Hattar's team, led by graduate students Tara LeGates and Cara Altimus, posited that mice would react the same way, and tested their theory by exposing laboratory rodents to a cycle consisting of 3.5 hours of light and then 3.5 hours of darkness. Previous studies using this cycle showed that it did not disrupt the mice's sleep cycles, but Hattar's team found that it did cause the animals to develop depression-like behaviors.
"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," he said. "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."
The animals also had increased levels of cortisol, a stress hormone that has been linked in numerous previous studies with learning issues. Treatment with Prozac, a commonly prescribed anti-depressant, mitigated the symptoms, restoring the mice to their previous healthy moods and levels of learning, and bolstering the evidence that their learning issues were caused by depression.
According to Hattar, the results indicate that humans should be wary of the kind of prolonged, regular exposure to bright light at night that is routine in our lives, because it may be having a negative effect on our mood and ability to learn.
"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," he advises.
Since they exposed the mice to equal amounts of light and darkness, how do they know it wasn't sitting in the dark for 3.5 hours that got the mice all upset? I'm pretty sure i'd be upset if you left me in the dark for a fraction of that time. Unless i was asleep. Then i don't know what the hell's going on.
Usually, i go around shutting off lights in every room we're not currently occupying, but lately, i've been toning down that particular OCD (hey, i'm trying to keep the electricity bill down. i also can't stand having a tv on that nobody's actively watching. it's like having something constantly droning in your ear but you can't quite catch the words.) because i thought i was being a little weird, cocooning us in a little bubble of light surrounded by darkened rooms. But, mebbe i should go back to doing that.
On a separate note, i want to put my vote in for going back to the way things were, as mentioned at the top of this article - let's all go to sleep when the sun sets and wake up when it rises. I can tell you right now that it's looks like the friggin middle of the night at 6:30 (when i have to get up for work) from December to most of March, and i hates it, Baggins.