Ever wonder why you don’t sleep well the first night in a new place? New research may explain the phenomenon.
Writing in the journal Current Biology, researchers from Brown University suggest that one-half of the brain “remains more awake” than the other, apparently to keep us prepared for potential trouble.
The so-called “first-night effect” is commonly experienced by frequent travelers who often notice less restorative sleep during the first night in a hotel or other location. The phenomenon is also a problem for sleep scientists because test subjects are likely not to sleep well the first night in a sleep lab.
"In Japan they say, 'If you change your pillow, you can't sleep,'" said corresponding author Yuka Sasaki, research associate professor of cognitive linguistic and psychological sciences at Brown. "You don't sleep very well in a new place. We all know about it."
To reach their conclusions, the researchers conducted three experiments to monitor brain activity over two nights of sleep, a week apart. Among the 35 participants, the researchers found that during the first night, the left hemispheres of the subjects' brains stayed more active than the right.
Subjects, they found, were more easily awakened when researchers stimulated the left brain by playing “irregular beeping sounds” into the subjects’ right ear. They found that “a particular network in the left hemisphere remained more active than in the right hemisphere, specifically during a deep sleep phase known as "slow-wave" sleep.”
During other phases of sleep, there didn’t appear to be any difference in activity between the two hemispheres.
On the second night of sleep, however,“there was no significant difference between left and right hemispheres even in the "default-mode network" of the left hemisphere, which does make a difference on the first night.”
"To our best knowledge, regional asymmetric slow-wave activity associated with the first-night effect has never been reported in humans," the authors wrote.
While the researchers believe their findings explain the first-night effect, they are still not sure what happens during other phases of sleep apart from the slow-wave phase. For example, they do not know if the left hemisphere “keeps watch all night, or works in shifts with the right later in the night.”
The default-mode network is also responsible for daydreaming during waking hours, according to some researchers and appears to remain active even when the rest of the brain may be less active.
Questions remain, however.
For example, researchers don’t know if other parts of the brain can enter an alert state in other phases of sleep.
"The present study has demonstrated that when we are in a novel environment, inter-hemispheric asymmetry occurs in regional slow-wave activity, vigilance and responsiveness, as a night watch to protect ourselves," the study concludes.