Have you ever had trouble sleeping in a new place?

Lots of people do. And now researchers from Brown University in Rhode Island think they know why.

They found that one-half of the brain "remains more awake" than the other half when people are trying to sleep in a new place.

This appears a case of the brain keeping people ready for trouble in a new place, the researchers said.

The sleep findings were reported in Current Biology and by Brown University.

In their report, the researchers said many people report they have a harder time sleeping the first night at a hotel or other places outside their home.

They call it, "first-night effect."

"In Japan they say, ‘if you change your pillow, you can't sleep,''' said Yuka Sasaki, one of the report's authors. "You don't sleep very well in a new place. We all know about it."

The researchers measured brain waves for 35 volunteers over two nights in a laboratory. The two nights were a week apart.

They found during the first night the left hemisphere of the brain was more active than the right hemisphere. This was during the first deep-sleep period, the researchers said.

Sasaki said a lot of questions remain.

Researchers did not keep measuring brain waves all night long. So, they don't know if the left hemisphere keeps "watch" all night. Or whether it "works in shifts" with the right hemisphere later in the night.

They also do not know why the extra brain activity, at least during the first phase of deep sleep, is always on the left hemisphere.

For some, this research may be calming. It is good to know that our brain is "looking out for us," in a new place.

But it may not help with sleep. That extra brain activity, at least according to this new research, makes it harder to get the sleep people need to wake up well rested in the morning.

I'm Bruce Alpert.

VOA News reported on this story for VOANews. Bruce Alpert adapted this story for Learning English. Hai Do was the editor.

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pillow – n. a bag filled with soft material that is used as a cushion usually for the head of a person who is lying down

hemisphere – n. either of the two halves of the brain

active – adj. doing things that require energy

shift – n. work done in a period of time