The best time for sleeping

I just spent an interesting few days at the annual meeting of the National Association of Science Writers. At the meeting, we learned a lot about a wide range of topics, not the least of which was science. I was fortunate enough to have lunch one day with a sleep researcher from Washington State University. And, if you recall from some of my previous posts, I think that sleep is a really fascinating scientific topic! One thing I learned from this sleep scientist is that everyone has an optimal time of the day in which to fall asleep. This depends largely on your circadian rhythms.

I bet that you've heard of circadian rhythms before - but do you know what they really are?

Circadian rhythms are 24-hour (roughly) cycles that occur in the physiology of all living beings - animals, plants, and even bacteria. Human circadian rhythms are those cyclical changes that occur in our bodies during a 24 hour period. The rhythms are controlled by something called the superchiasmatic nucleus (or SCN), which is a pair of structures in your brain about the size of a pinhead. The SCN, containing around 20,000 neurons, sits in the brain just above where your optic nerves cross. Different levels of light that hit your eyes are translated into a signal for the SCN, which then regulates multiple physiological processes. These processes mostly relate to the sleep/wake cycle - body temperature, blood pressure, brain activity and hormone secretion. In particular, when it gets dark, our brains signal the secretion of melatonin, a hormone that makes us feel sleepy.

Now, while our circadian rhythms are regulated by the light/dark cycle around us, they do not absolutely require it! Animals kept in total darkness for an extended period of time will have what is called a "free running" rhythm - the rhythm is still there, it's just not dependent on light levels. In fact, blind subterranean mammals (such as blind mole rats) maintain their endogenous clocks without any external stimulus. (That's good news for those of us who live far enough north that the winter months have significantly more darkness than daylight.)

Even for blind rodents living in the dark, circadian rhythms help determine the optimal time for an organism to go to sleep. And since everyone's circadian rhythm is different from everyone else, so is their best sleep time. How do you determine what your ideal bedtime is? The answer is called a sleep latency test.

A sleep latency test is based on the premise that, as you get sleepier, the amount of time it takes you fall asleep decreases. If you were to lay down in a dark room with nothing to do, eventually you will fall asleep. How long it takes you to do so is called your sleep latency. If you are wide awake, it will take you a long time; if you are sleepy, it won't take very long at all. Your ideal bed time is that time of day when you have the shortest sleep latency. If you try to fall asleep before then, it will take you a longer time. Interestingly enough, if you stay awake past that point, it will also take you longer!

If you want to find out your ideal time to sleep, this sleep scientist said that conducting a sleep latency test is very easy to do (though you need someone to help you). For a few nights, go to bed at different times (8:00pm, 9:00pm, 10:00pm and 11:00pm, for example). Have someone monitor you to see how long it takes you to fall asleep. Whenever you fall asleep the fastest is the closest optimal bed time for your circadian rhythm. Of course, this test must be done when you are not sleep deprived, or that will skew the results. (If you're tired enough, it may not matter what time you lie down, you might go right to sleep regardless!)

I believe that I know roughly my optimal bed time, but I would be interested to try this to see whether I'm right or not. Does anyone else want to try it?