Many of us have had this experience： we lie down in a bed other than our own， perhaps at a friend's house or in a hotel room， and find it difficult or impossible to fall asleep． Is it because the bed is uncomfortable？ Maybe， but perhaps there can be other reasons．
According to a new study published in Current Biology， a significant reason is what the scientists call "first night effect"． They believe that one side of the brain acts as a "night watch" to warn us about potential dangers． It forces us to stay awake on the first night in a new environment．
For the study， 35 young volunteers were asked to sleep in a sleep lab for several days． Meanwhile， researchers watched their brain activities．
According to the researchers， on their first night， the left brains were more active than the right brains and people had a hard time sleeping． However， left-brain activity decreased as days went by， falling even to the point of complete calm． In this process， the participants got an increasingly better sleep experience．
The findings suggest that the different rhythms of the sides of the brain affect our sleep． When the two sides work differently， the balance between them is broken． Thus， the brain can't relax and is sensitive to anything strange in the surroundings， just as it is in daytime．
"At some level， the brain is continuing to analyze things， even though you are not aware of the analysis，" US professor Jerome Siegel told Smithsonian Magazine． "If something unusual happens - if a door opens or you hear a key in a lock - you can be alert， even though the intensity of the stimulus is quite low．"
More surprisingly， this phenomenon is similar to the way some animals sleep． Whales， dolphins， and many birds can sleep with half of their brain while the other half stays awake， with its corresponding eye staying open．
The researchers think that it is the result of evolution， and works to protect us in potentially dangerous environments．
If you have ever had what you think is "first night effect"， researchers suggest that you bring your own pillow or sleep in a room similar to your bedroom next time you sleep away from home．



What did the new study published in Current Biology find？ ______

A. A comfortable bed could help people sleep well in a new environment．
B. Most people could sleep well in a new environment after the first night．
C. Brain activities affected people's sleep in a new environment．
D. The right brain determined how well people slept in a new environment．

What was found out about the volunteers？ ______

A. Their left brains were more active on the first night．
B. Their right brains became more active as days went by．
C. Their right brains kept them awake the whole night．
D. They slept better in the sleep lab than at home．

What do the researchers think makes the brain sensitive to new things？ ______

A. The bad sleep experiences people have had．
B. The tiredness that people suffer from in daytime．
C. The imbalance between the two sides of the brain．
D. The strangeness of the things that people come across．

What do the researchers think of "first night effect"？ ______

A. It has evolved as a way to protect us．
B. It's a characteristic that animals don't have．
C. It's completely different from the way animals sleep．
D. It helps people to get used to new environments quickly．