Over the course of three experiments on 35 young, healthy
volunteers, researchers measured brain activity during two
consecutive nights of slumber. They consistently found that part of
the left side of the brain remained more active than the right side
only on the first night, specifically during a deep sleep phase
known as slow-wave sleep.
“When you sleep in a new place for the first time, a part of one
side of the brain seems to stay awake for surveillance purposes, so
you could wake up faster if necessary,” said senior study author
Yuka Sasaki of Brown University.
While this may be bad news for business travelers who regularly make
brief overnight trips, it may not be as troublesome for people who
go away for longer periods of time, Sasaki added by email.
“Frequent travel may lead to unrestful sleep,” Sasaki said. “But if
you stay for a few days at the same place, your sleep might catch
To see how being in a strange place impacts sleep, Sasaki and
colleagues performed a series of lab tests on their subjects.
When they stimulated the left hemisphere with irregular beeping
sounds in the right ear during deep sleep on the first night, that
prompted significantly greater likelihood of waking and faster
action upon waking, than if sounds were played in the left ear to
stimulate the right hemisphere.
In other sleep phases during the first night, and with other tests,
there wasn’t any difference in alertness or activity between the two
hemispheres of the brain, the researchers report in the journal
On the second night, there wasn’t any difference in reactions to
tests between the left and right hemispheres, even during deep
This suggests that there is a first-night-only effect specifically
in one hemisphere of the brain during deep sleep, the authors
conclude. The way participants responded to the sleep lab tests
points to the potential for the brain to be on high alert for danger
during the first night in unfamiliar surroundings.
Some birds have been found to literally sleep with one eye open and
one side of the brain awake when they’re in a dangerous setting, and
some marine mammals have similar abilities, the authors note.
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One limitation of the new study is its focus on healthy volunteers,
which means the results may not apply to people with insomnia or
other sleep disorders, the authors note.
While it’s possible that the findings may explain poor sleep among
frequent travelers, the study wasn’t designed to test whether these
“first night effects” continue to happen to people every time they
hit the road, said Patrick Finan, a psychiatry and behavioral health
researcher at Johns Hopkins University School of Medicine in
“It is possible, for example, that frequent travelers might adapt to
this first night effect over time,” Finan, who wasn’t involved in
the study, said by email.
“Any clinical implications would be speculative at the moment,”
Finan added. “However, the level of specificity provided by these
analyses could be an important first step in understanding who might
be at risk for sleep disorders like insomnia, which is thought to be
driven in many patients by chronic hypervigilance.”
SOURCE: http://bit.ly/1wE10JV Current Biology, online April 21,
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