Light at night causes changes in brain linked to depression

Exposure to even dim light at night is enough to cause physical changes in the brains of hamsters that may be associated with depression, a new study shows.

Researchers found that female Siberian hamsters exposed to dim light every for eight weeks showed significant changes in a part of the brain called the hippocampus.

This is the first time researchers have found that light at night, by itself, may be linked to changes in the hippocampus.

These alterations may be a key reason why the researchers also found that the hamsters exposed to dim light at night showed more depressive symptoms when compared to hamsters in a standard light-dark cycle.

"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," said Tracy Bedrosian, co-author of the study and doctoral student in neuroscience at Ohio State University.

Bedrosian and her colleagues presented the results Nov. 17 in San Diego at the annual meeting of the Society for Neuroscience.

The results are significant because the night-time light used in the study was not bright: 5 lux, or the equivalent of having a television on in a darkened room, said Randy Nelson, co-author of the study and professor of neuroscience and psychology at Ohio State.

"You would expect to see an impact if we were blasting these hamsters with bright lights, but this was a very low level, something that most people could easily encounter every night," said Nelson, who is also a member of Ohio State's Institute for Behavioral Medicine Research.

The study involved female Siberian hamsters, which had their ovaries removed to ensure that hormones produced in the ovary would not interfere with the results.

Half were housed in a standard light-dark cycle of 16 hours of light (at 150 lux) and eight hours of total darkness. The other half were housed in 16 hours of daylight (150 lux) and eight hours of dim light (5 lux).

After eight weeks in their lighting condition, they were tested for depressive-like behaviors. These tests are the same ones used by pharmaceutical companies to test anti-depressive and anti-anxiety drugs in animals before they are used in humans.

One depression test, for example, measured how much sugar water the mice drank. Mice generally like the drink, but those with depressive-like symptoms will not drink as much, presumably because they don't get as much pleasure from activities they usually enjoy.

Results showed that hamsters that lived in the dim light at night showed more symptoms of depression compared to the hamsters in the standard light-dark cycle.

At the end of the experiment, the researchers examined the hippocampus area of the hamsters' brains.

Results showed that mice that lived in the had a significantly reduced density of dendritic spines – hairlike growths on brain cells, which are used to send chemical messages from one cell to another.

"The hippocampus plays a key role in depressive disorders, so finding changes there is significant," Bedrosian said.

The researchers found no difference between the two groups of in terms of concentrations of the stress hormone cortisol. That's important because hormones like cortisol have been linked to changes in the hippocampus.

"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," Nelson said.

How is light at night causing the changes in the hippocampus? The researchers believe it is related to production of the hormone melatonin. Light at night suppresses secretion of melatonin, which is involved in how the body knows it is nighttime.

The lower levels of melatonin at night may be the cause of the lower density of dendritic spines in the , Bedrosian said.

The researchers are continuing this work by investigating the exact role of melatonin in the findings of this study.

These results are consistent with an earlier study by Nelson and his colleagues which found that constant bright light at night is linked to in male mice. In another recent study, they found that light at night is also linked to weight gain in mice. Provided by The Ohio State University

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Nov 17, 2010
Yes there's a link...based on one study with female Siberian hamsters. Don't start generalizing to humans just yet.

Nov 17, 2010
I have a sample of 5 million humans that says otherise.

In Finland, the nighttime illumination exceeds 5lux from May to early August. Finns are not at all depressed during the Summer months. On the contrary, that is exactly when most of them feel exhilarated, outgoing and social.

October to December are the hardest months for most Finns. This can be verified by monthly statistics of anti-depressant intake, suicides, and domestic violence. (In spite of this, Spring seems to be the top season for suicides, but some argue that this is when people who have been seriously depressed the entire winter notice that others are rising, and they can't keep up.)

I'd say this is an example of not everything being the same between arbitrary animals and humans. They might also want to study these Siberian hamsters in cages or outdoor labs in Siberia, to cross check their findings.

Nov 17, 2010
outdoor light doesn't matter, only the amount of light in the room where the human is sleeping. you'd have to find out if fins sleep in rooms with lots of light during the summer or if they use heavy curtains to keep it dark. Lots of research throughout the years have found various physiological effects to sleeping with light.

Nov 17, 2010
I have one of those clocks that shine the time on the ceiling,and I get the glow from streetlights through my bedroom window,and other gadgets in my room.I am not depressed,but maybe the light is affecting me somehow.I bought one of those sleep masks.Maybe it will improve the quality of my sleep.

Nov 18, 2010
@thewhitebear: Finns don't usually have light-tight curtains. The illumination in the bedroom exceeds that of "a TV left on", during the summer months.

Nov 18, 2010
I wouldn't give much weight to an article that can't decided whether they were studying hamsters or mice.

Nov 18, 2010
Mice or hamsters, whichever: the only ones I've met are nocturnal. Most people sleep in the dark; most hamsters are up and about. Seems to me the light affecting the little furries when they're up running in their wheels shouldn't have much at all to do with us. Any mention of this is lacking in the article.

Nov 18, 2010
I agree with delayed2sleep. Constant light should inhibit nocturnal animals from being active. It's not surprising that would lead to depression. Light does not inhibit activity in humans.
In a diurnal rodent, the sand rat, too little light (only 5 hours per 24 hour day) causes depression.
In humans, psychiatric researchers have found light to have an antidepressant effect. Depression is more frequent in winter and mania in summer. And the example of the Finns and other Northern peoples, as cited by gwerde, supports this.
It's an interesting study, but should not be applied directly to humans.

Nov 18, 2010
These sorts of studies are useless. Apparently the researchers are unaware that our planet is circled by a moon that gives off a lot more light than that and we have stars up in the sky that give enough light to see by even when the moon is not available. This is true out in the rural areas where I live. I realize the city folk who are doing this research probably never know what night time is really like.

Nov 18, 2010
I would assume that some effects on a "conscious" animal, such as humans, may be the opposite of that on a less complex animal. Given that humans associate information by relating it to preconceived insight on the topic, our response to stimuli is entirely subject to our notions on what that might be.
If this were not true, our responses would rely wholly on instinct, and we would not change from our nature. That is to say, we would all be very predictable (or at least a more simplistic level).

Example being that one may relate moonlight to an exciting memory, and may actually incite adrenaline or drive rather than depression.

The conclusions are rash.

Nov 19, 2010
A light at night causes me to have more vivid dreams that are easier to remember. Doesn't depress me a bit.

Nov 22, 2010
The full moon maxes out under 1 lux, so that is under the illumination tested here, which is close to the end of twilight.

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