Does light control your mood?

A couple weeks ago, I wrote about a study involving mice...and circadian rhythms: too much low light (day or night ) or insufficient bright light (during the day) can mess with circadian rhythms and cause bodily fatigue, jet lag, seasonal effective disorder, whatever you want to call it. It made me glad I walk to work in the bright sunshine every day and sad that my bedroom wall has big floor-to-ceiling windows.

This week, I read another study involving hamsters...and circadian rhythms: too much low light at night causes specific changes in the brain AND symptoms of depression (i don't know how precise you can get at judging whether a hamster is depressed.) Researchers exposed one group of the furry fellow to low light every night for 8 weeks, and found the hamsters hippocampus changed, though there was no change in the level of cortisol, a stress hormone. That made researchers pretty sure the changes were a result of the light and not the lab conditions. In the hippocampus, scientists actually observed fewer hairlike growths, used to make chemical connections, on brain cells.

Both studies are quick to relate extreme fatigue and depression to low light exposure during the night. I wonder if this will pan out in clinical tests of humans. If so, I'm gonna totally rethink my sleeping schedule, buy some blackout curtains, and never take the red-eye.

Altimus CM, Güler AD, Alam NM, Arman AC, Prusky GT, Sampath AP, & Hattar S (2010). Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities. Nature neuroscience, 13 (9), 1107-12 PMID: 20711184