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ROVIDENCE, R.I. — To most scientists, discarding data is like throwing money in the trash. But for sleep researchers, it’s routine to get rid of half of the findings from every experiment.

That’s because most people sleep badly their first night in a new place, whether it’s in the closely monitored hush of a sleep lab or a wind-whipped tent in the desert. And so researchers consistently discard their observations from someone’s first night in the lab, only paying attention to the second, when participants have fallen back into their usual nighttime rhythms.

Now, neuroscientist Masako Tamaki and her colleagues at Brown University have turned what was once considered scientific garbage into a goldmine.

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In a paper published Thursday in Current Biology, they revealed the brain science behind our restless shut-eye when we arrive in a new place, finding that certain circuits in the left side of our brains remain aroused while the rest of the brain slumbers more deeply.

“Sleeping for the first night in an alien environment puts us in a state of hypervigilance,” said Thomas Roth, a sleep researcher at the Henry Ford Hospital in Detroit, who was not involved in the study. “We did not know that until this paper.”

Perhaps the finding shouldn’t come as a surprise given our evolutionary past. Seals, for example, keep one whole side of their brain turned on when sleeping out in the water, while their entire brains surrender when they nap on the beach. Birds do something similar.

To figure out what was going on in humans’ brains — and help explain the so-called “first-night effect” at a neuroscientific level — Tamaki and her team didn’t ask participants to sleep out in the ocean. Instead, they brought 35 young, healthy volunteers into a soundproofed sleep chamber in their basement lab here at Brown.

It looks comfortable, with beige shag carpeting and a thick blue comforter covering a double bed — but this pod is more closely watched than any Soviet hotel room.

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There isn’t just a camera in the corner. Participants are also asked to wear a strange cloth wig covered with electrodes. It looks like a cross between a sea creature and a robot. The study subjects have already had bluish gel squirted into their hair, so the electrical activity of their brains can be transmitted into these metal tips and sent zinging along the wires, which run through a hole in the wall and straight into a computer.

By comparing the electrical activity data to two kinds of imaging, the researchers could map out what was going on where in the brain. In seals, it might be one whole hemisphere that stays aroused when sleeping in the water, but in humans Tamaki and her colleagues found it was just the left side of an interconnected brain region called the default mode network.

This network is sort of our brains’ equivalent of a screen saver: when you’re not focused on a task, the default mode network takes over. And during the first sleeping session in the study, the default mode network was more active — and the participants were more likely to respond to beeping sounds — while that effect disappeared once the study subjects were familiar with sleeping in the lab.

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“We don’t know whether the new environment is safe,” said Tamaki. “So perhaps we need to keep a brain network partially awake so that we can monitor the environment and wake up faster. If both hemispheres are fast asleep it might be difficult to respond to unusual situations, like someone coming into the room to attack you.”

The study only offers a first glimpse into the brain’s activity when we’re sleeping for the first time in a sleep lab, hotel room, or the bed of a one-night stand. And according to Dr. Raj Dasgupta, a sleep specialist at the University of Southern California’s Keck School of Medicine, the kind of a sleep Tamaki’s team measured slowly disappears with age, making it hard to extrapolate these results to everyone.

The research also offers only explanations — not solutions — to the first-night effect. And people will still feel just as groggy when they walk off a red-eye. But at least scientists can now pinpoint the network of neurons that’s partially to blame.

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