It's the curse of traveling or spending the night at a friend's place: your friend is immediately out like a light, but for some reason, it takes you forever to get to sleep, and you can't seem to get enough rest, no matter what you do. No, you don't have this problem just because you're a terrible houseguest or the princess with the proverbial pea (though I'm sure a deflating air bed never did anybody's sleep quality any good) — a new study from Brown University, reported in the journal Current Biology, has discovered why almost every human has a bad night of sleep when they're in a new place. And weirdly, it seems to be because part of our brain is still afraid of saber-toothed tigers.
It turns out that the reason we have a hard time falling and staying asleep when we're in a new place is an issue of brain symmetry (though for the record, subjects of the study spent the night in a sleep lab, where they were plugged into a machine that read their brain waves — which wouldn't make me very comfortable, either). One brain hemisphere is more active than the other when you're sleeping in a new place, and we're not entirely sure why, but it may be because our brains want to be more aware in a strange environment. What's actually in that hotel bathroom? You think it's just towels and a fancy shampoo you've already decided to steal, but are you really sure? Maybe there are Japanese fighting spiders.
So yes, you can blame your grumpiness on your first night on vacation on an uncooperative (or just overprotective) brain. Not on the fact that your friend snores. No, not that at all.
The Left Side Of Your Brain Stays Awake And Keeps Watch
The study found that for the first night of sleep in a strange place, the human brain actually sleeps asymmetrically; that is, the two hemispheres, left and right, react differently. In subjects left to sleep in the lab for the first time, the left brain's nerve cells showed much less activity related to sleep than the same area on the right side. In other words, the left side was more "awake", and reacted more to stimuli like quiet sounds than the right side. Turns out you toss and turn because your brain isn't fully asleep; at least part of it is keeping an eye open.
This makes excellent sense, from an evolutionary perspective. Humans aren't exactly the most well-protected of creatures (we're soft and ever so fleshy), and we're particularly vulnerable when we're asleep, as anybody who's ever been tackled in their beds by well-intentioned children will know. In places you recognize as safe for sleeping, like your bedroom, your brain has determined that there's a low chance of threats, and allowed itself to enter sleep fully on both sides of the brain. But in foreign environments, how's your brain going to know there isn't a strong chance of a bear coming out of the closet? Or enemies jumping in through the B&B window? (Apologies if I just ruined your sleep forever.) A bit of wakefulness sucks, but it's designed to keep us safe.
The asymmetry disappeared on the second night the subjects spent in the lab, presumably because there was enough evidence of safety for it to relax. But it's a good explanation for why the first night anywhere unfamiliar is likely to drive you nuts.
...But It Might Not Stay Awake All Night
Here's something interesting about the study: it only studied the first of the many slow-wave movements across a night's sleep. Sleep, in case you didn't know, has different stages or waves, and slow-wave sleep is one of the times when the body relaxes, unlike REM or rapid eye movement sleep. The scientists only collected data on the brains during the first of these waves, but they recur over the course of a good night's rest, and that raises a few interesting possibilities.
Do the two brain hemispheres take turns? Does the right brain "take over" at any point and keep watch while the left brain sleeps? The researchers weren't able to pinpoint anything specific about the left brain's wakeful neural network that meant it should be the one on alert. It could be that we sleep badly because our brain hemispheres, like parents, are switching back and forth, watching over us while trying to snatch a bit of sleep. It's kind of cute, really.
Or it might just be that way for the first few hours of sleep, and then everything's hunky-dory and the entire brain gets to sleep.
And it's not clear at all how this affects dreams. The point is that we're not sure; it's a weird phenomenon, and previously scientists thought that only other animals, like rats, experienced "asymmetric sleep." When it comes to the science of sleep, we're still kind of in the dark (sorry).
Unfortunately, we don't know if there's any way to "trick" your left hemisphere into calming down and letting you get a good night's rest on the first night in a new place, even if you're categorically, absolutely sure that there's no way anything's lurking anywhere sinister. (You checked under the bed, right?) So we may know why, but we can't stop it from happening. Sorry.
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