Sometimes mother or father really did know best. For example, when they told us “You have school tomorrow. If you want to do well, turn out the light and go to bed.”
Now comes a report from researchers at Ohio State University that may indicate just how right they were. Working with female Siberian hamsters, co-authors Randy Nelson, professor of neuroscience and psychology at Ohio State, and doctoral student Tracy Bedrosian have shown that even a dim night-light may cause physical changes in the brain linked to depression. Presented on November 17 in San Diego at the annual meeting of the Society for Neuroscience, it is the first study to definitively show that by itself light at night may be linked to changes in the hippocampus, an area of the brain vital in regulating mood and learning.
The researchers exposed the hamsters to dim light for eight weeks and learned that “Even dim light at night is sufficient to provoke depressive-like behaviors in hamsters, which may be explained by the changes we saw in their brains after eight weeks of exposure,” reported Bedrosian. Most importantly (and surprisingly), the light used was only 5 lux – the same as having a television on in a dark room.
“You would expect to see an impact if we were blasting these hamsters with bright lights, but this was a very low level, something most people could easily encounter every night,” noted Nelson, a member of Ohio State’s Institute for Behavioral Medicine Research.
During the study, half the hamsters lived in 16 hours of daylight at 150 lux and eight hours of light at 5 lux; the other half had a light-dark cycle of 16 hours at 150 lux and eight hours of complete darkness. After eight weeks, the dim-light hamsters displayed more depressive behaviors compared to the control group and the researchers found that the dendritic spines in their hippocampi had far less density. Dendritic spines are hairlike growths on brain cells, which are used to send chemical messages from one cell to another. No differences between the two groups were found in the levels of the stress hormone cortisol. This is important because cortisol had previously been associated with changes in the hippocampus.
“The hippocampus plays a key role in depressive disorders, so finding changes there is significant said Bedrosian. “To the best of our knowledge, this is the first study to document that light at night is a sufficient stimulus to induce changes in the hippocampus, without changes in cortisol levels.”
It may be that the brain changes are linked to the production of melatonin, a hormone that helps the body know when it is nighttime, and lower levels of melatonin at night may explain the lower density in dendritic spines in the experimental hamsters.
“The moral of this story is simple,” said Francis J. Flynn, Psy.D., CAP, president of the Brain Training Centers of Florida. “Whether you’re a child, an adolescent or an adult, make sure your sleep environment is as absolutely dark as possible, cover up alarm clocks and turn off televisions. And you probably don’t need that nightlight as much as you think – not if you want to avoid depression and learn as well as possible.”
Francis J. (Skip) Flynn, Psy. D.
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