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Science. Communication. Community.

What makes us tick?

No matter how much we try to work around the clock or go off the grid, we’re never free from our circadian rhythms.

by Kerstin Nordstrom

Midnight Sun in Iceland, via Wikimedia Commons

Last week, I returned from my summer vacation.  Accidentally and appropriately, my in-flight reading was the novel The Age of Miracles by Karen Thompson Walker. It’s a coming-of-age story that coincides with a science fictional premise: the rotation of the Earth is slowing down. Every living thing’s circadian rhythms are thrown into disarray, plants die, animal species go extinct, and humans get sick.

The topic was appropriate because I had just spent the middle of summer in Scandinavia, where and when the Sun doesn’t really set.

Some nights I spent in rooms with thick curtains and slept well. But some nights I spent in rooms with thin curtains and slept less well. And some nights I was in a tent, and just tried to sleep as much as I could. I always seemed to have some manic energy around midnight, and wanted to sleep more in the morning, but just couldn’t.

Why was my sleep clock wacky? It’s those darn zeitgebers.

All of us have a master body clock in the suprachiasmatic nucleus (SCN), a small area of the brain. But the SCN is not a true master, it’s cued to action by external factors: zeitgebers. The primary zeitgeber is light. When light stops hitting our eyes at night, the SCN tells our body to produce melatonin, the sleep hormone. When light starts hitting our eyes in the morning, the melatonin production slows.

Other zeitgebers include food, exercise, and social stimulation. Remember how easy it was to stay up all night at slumber parties? You ate all night, played hide and seek, and chatted away.

Additionally, there seem to be other clocks that run independently of the master. Our body temperature drops and cortisol levels in our body increase at night. There also are so-called “peripheral oscillators” in skin cells, in lung cells, and so on.

But all of these clocks seem to be on the same timetable: 24 hours.

Experiments have been done to try and mess with the light cycle. In one experiment, subjects were exposed to 28 hour day/night cycles, aka 6 days per week [1]. The subjects adapted to sleep with this schedule, but the other clocks in their bodies never adjusted and kept on the 7 day per week schedule.

This is why we experience jet lag, the feelings of blah and disorientation that come with crossing time zones. The light cues conflict with our body clocks, and our body clocks may never fully adjust during our visit. We’ve messed up our rhythms.

It’s also why folks with mood disorders, such as depression, need to be especially careful with their sleep schedule, light exposure, and jet lag. Melatonin and cortisol are hormones that drastically affect moods.

In fact, there’s a stereotype about the Scandinavians: they’re all depressed because of the never ending winter nights. They all get seasonal affective disorder (SAD).

But taking a survey of the Swedish and Norwegian friends I met on the trip, they think that’s silly. They’re used to it.

And the science is now suggesting that they are in fact more immune to sleep disturbance and SAD because they are used to it [2-4]. It’s possible that their bodies pick up more subtle changes in light than people who live on lower parallels, or there is some other zeitgeber in the mix. As far as high depression rates, the numbers don’t lie. Research by the World Health Organization has suggested that depression is generally higher in wealthy countries. The good old US of A beats every country in depression rates, and no Scandinavian country is in the top ten.

By the time I returned home, I was mentally used to the light cycle, though not biologically. On the bus ride back to my house, I was almost shocked to see the Sun setting. I slept like a log that night.

[1] http://www.sciencemag.org/content/284/5423/2177.abstract

[2] http://scienceblogs.com/clock/2007/02/11/small-arctic-mammals-entrain-t/

[3] http://ajp.psychiatryonline.org/article.aspx?articleID=173951

[4] http://www.biomedcentral.com/1471-244X/12/225

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One comment on “What makes us tick?

  1. Timely post! I just got back from a trip to Southeast Asia, and I’m recovering from jet lag as well. The time difference (11 or 13 hours, depending on how you think about it) means that I’m naturally most tired between about noon and 6 pm here, but by the time I go to bed, my brain is wide awake and uncooperative. I’m trying to get plenty of light to reset (and plenty of dark at night), but right now it’s incredibly frustrating!

    A few years ago I was in Sweden in late June and early July, and it was crazy how little sleep I needed. I just wasn’t tired as much when I was getting so much light!

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This entry was posted on July 26, 2013 by in Health.
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