Night shift workers

So, how does the clock reset itself?
Here's the short answer. The long answer is a beautiful example of brain science; I'll send you there in a minute if you're interested. Briefly then: every morning light turns off a chemical process and allows the clock process, which is a very interesting string of chemical reactions, to start all over again. Clock researchers have identified all the important molecules in this process. Lo and behold: lithium directly affects one of the key enzymes in the resetting of the clock. Here we find "ground zero" of our biological rhythms, the very center of the clock process, and there's lithium right in the middle of it. Very interesting. If that's enough to get you interested, have a look at the long story about how the clock works, including how lithium affects it.



"Light is central to biological rhythms -- and so is DARKNESS
If light starts the clock every day, is it possible that darkness is a necessary ingredient as well? Look at the question this way: sleep deprivation can cause manic episodes. In part that's too little sleep itself -- but might part of the story be "too much light?" Generally when people are sleeping less and heading toward mania, they're not hanging out in the dark. They're up late at night in very well lit places, like casinos, roadways with bright car lights in their eyes, their office preparing the big talk that will secure their future millions, and so forth. They're not sitting in some dark room. Is there any chance that being forced to stay in the dark during an emerging manic episode could actually turn them in the other direction? We'll look at some evidence for that in just a moment.

Here's another angle on light and dark: suppose that the appearance of light every morning can reset your clock only when you've had enough darkness. Maybe the brain needs to be able to see the contrast? What would happen if you didn't get enough darkness? Maybe you'd lose your biological rhythm entirely; your body wouldn't know when to make you sleep and when to wake you up. You'd be up in the middle of the night sometimes, for days in a row, backwards to real time. Then you might be so asleep during the real day you could hardly get out of bed; getting up in the morning would feel like getting up from sleep in the middle of the night does for the rest of us, ugh."