If you have ever spent the night in an unfamiliar place and woken feeling a bit groggy, scientists might have the answer. A study in the journal Current Biology suggests that one half of thebrain may stay alert to act as a kind of ‘night watchman’.
“We know that marine animals and some birds show unihemispheric sleep, one awake and the other asleep,” explains Yuka Sasaki of Brown University in the US, who led the study. She says in a statement that while the human brain doesn’t show the same degree of asymmetry that the brains of marine animals do, the new findings suggest that “our brains may have a miniature system of what whales and dolphins have.”
Researchers have acknowledged that people often sleep poorly in a new environment. It’s why scientists in sleep laboratories ignore data gleaned from volunteers on their first night.
Yuka Sasaki and colleagues wanted to examine what lay behind this ‘first night’ phenomenon.
The team measured brain activity during 2 nights of sleep, a week apart, among 35 volunteers.
They found that during the first night in the lab, part of the left hemisphere of the brain remained more active than the right hemisphere, especially during deep, or ‘slow wave’, sleep.
When the researchers stimulated the left hemisphere by playing beeping noises in the right ear, the volunteers were more likely to be roused and to wake up faster.
However, on the second night there was no significant difference between left and right sides of the brain.
The researchers say they do not yet understand why it is always the left side of the brain that is more active during the first night sleeping in an unfamiliar place.
Yuka Sasaki says people might be able to reduce the ‘first night’ effect by bringing familiar objects such as their own pillow or staying in the same kinds of hotels where layout and decorations are familiar.
It’s also possible that people who have to sleep in new places can learn to turn off their night watchfulness mode. “Human’s brains are very flexible,” she says. “Thus, people who often are in new places may not necessarily have poor sleep on a regular basis.”
Source: ‘Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans’, Sasaki et al, Current Biology.
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