When I’m tired, where exactly am I tired?
Rafael
Madrid, Spain
Two ironing women, by Edgar Degas. Musée d'Orsay
Well, it depends. What kind of “tired” are you talking about? If you’ve been exercising, the answer’s pretty clear, says James Krueger, a sleep researcher here at WSU. The tiredness is in your muscles. What’s not so clear, though, is how that tiredness relates to sleep.
This is an excellent example of the trouble that being scientific gets you into. If you don’t worry about the details, no big deal. You work hard. You get tired. You go to sleep. You wake up ready to go again.
But of course, the body isn’t quite that simple. Like everything else, the body is full of causes and effects. Connecting those causes and effects is the hard part. If you exercise heavily, says Professor Krueger, the number of white blood cells in your blood goes way up. White blood cells are the front line of your immune system. Also, your body produces all sorts of cytokines. These proteins regulate your immune system.
What’s interesting is that some of these cytokines are also involved in regulating sleep. And they’re also what give you that achy feeling when you’ve exercised a lot. Interestingly, even if you don’t exercise, but don’t get any sleep, your muscles will ache.
Now, if our science were perfect, at this point we’d put the pieces together and say AHA, this is what “tired” is all about. But all we can actually say is that some chemical signal is generated in your muscles, that signal is sent to your brain, and your brain interprets it as “tired.”
Speaking of your brain, that’s another story. Even though you feel tired when you don’t get enough sleep, your brain itself doesn’t really feel “tired.” In fact, according to some recent experiments, it seems that when you’re asleep, your brain is actually going over things from when you were awake. Some birds, for example, seem to rehearse their songs while they’re asleep!
So if your brain isn’t tired, why does it have to sleep? And how much of the brain goes to sleep when you’re asleep?
It doesn’t seem like single cells go to sleep, says Professor Krueger. On the other hand, we know that the whole brain doesn’t need to go to sleep for you to be “asleep.” Some animals, for example, go to sleep half a brain at a time. Some researchers recently found that when a flock of ducks goes to sleep, the ducks on the outer edge will sleep with one eye open and half their brain awake while the other eye and brain-half are asleep! Whales and dolphins also sleep a half-brain at a time. That’s how they keep from drowning while they sleep.
But back to “tired.” What IS that tired, groggy feeling you feel when you haven’t had enough sleep? “We really don’t know,” says Professor Krueger. You lose the ability to focus and concentrate. You don’t think clearly. You get uncoordinated. But what exactly does it mean? That’s part of what sleep researchers are trying to figure out. That – and why exactly we need to sleep.
Most of that tired feeling you get in your muscles can be cured by just resting. So why do we need to be unconscious for eight hours every night?
Professor Krueger believes that sleep helps the brain save its “synaptic superstructure.” What this means is that your genes gave your brain a certain pattern of synapses, or connections between neurons. During the day, your brain is constantly rearranging itself and reforming patterns and talking to itself in different ways. What sleep does, thinks Professor Kmeger, is shift these synaptic patterns back to their original design!
