Why Do We Need to Sleep? - The Atlantic - 0 views
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In a way, it’s startling how universal sleep is: In the midst of the hurried scramble for survival, across eons of bloodshed and death and flight, uncountable millions of living things have laid themselves down for a nice, long bout of unconsciousness. This hardly seems conducive to living to fight another day.
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such a risky habit is so common, and so persistent, suggests that whatever is happening is of the utmost importance. Whatever sleep gives to the sleeper is worth tempting death over and over again, for a lifetime.
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Biologists call this need “sleep pressure”: Stay up too late, build up sleep pressure. Feeling drowsy in the evenings? Of course you are—by being awake all day, you’ve been generating sleep pressure! But like “dark matter,” this is a name for something whose nature we do not yet understand.
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The search for the hypnotoxin was not unsuccessful. There are a handful of substances clearly demonstrated to cause sleep—including a molecule called adenosine, which appears to build up in certain parts of the brains of waking rats, then drain away during slumber. Adenosine is particularly interesting because it is adenosine receptors that caffeine seems to work on.
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For instance, if adenosine puts us under at the moment of transition from wakefulness to sleep, where does it come from? “Nobody knows,” remarks Michael Lazarus, a researcher at the institute who studies adenosine. Some people say it’s coming from neurons, some say it’s another class of brain cells. But there isn’t a consensus. At any rate, “this isn’t about storage,” says Yanagisawa. In other words, these substances themselves don’t seem to store information about sleep pressure. They are just a response to it.
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A few years ago, the group discovered a mouse that just could not seem to get rid of its sleep pressure. Its EEGs suggested it lived a life of snoozy exhaustion, and mice that had been engineered to carry its mutation showed the same symptoms. “This mutant has more high-amplitude sleep waves than normal. It’s always sleep-deprived,” says Yanagisawa. The mutation was in a gene called SIK3. The longer the mutants stay awake, the more chemical tags the SIK3 protein accumulates. The researchers published their discovery of the SIK3 mutants, as well as another sleep mutant, in Nature in 2016.