It's a well-established fact that dolphins and other marine mammals sleep with only one half of their brain. So called uni-hemispheric slow-wave-sleep (USWS) is not known in terrestrial mammals, only in marines and some birds. But, as always, humans are the weird exception. A Japanese team at Brown University published the first ever research showing that humans also practise USWS, especially when sleeping 'in an unfamiliar place'.
People who go to bed wary of potential danger sometimes pledge to sleep “with one eye open.” A new Brown University study finds that isn’t too far off. On the first night in a new place, the research suggests, one brain hemisphere remains more awake than the other during deep sleep, apparently in a state of readiness for trouble.
The team tested 35 volunteers in a sleep lab for a couple of nights, a week apart, using multiple methods.
They consistently found that on the first night in the lab, 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. When the researchers stimulated the left hemisphere with irregular beeping sounds (played in the right ear), that prompted a significantly greater likelihood of waking, and faster action upon waking, than if sounds were played in to the left ear to stimulate the right hemisphere.
“To our best knowledge, regional asymmetric slow-wave activity associated with the first-night effect has never been reported in humans,” the authors wrote.
Finally, Sasaki said it’s not known yet why the brain only maintains an alert state in just one hemisphere – whether it’s always the left or in alternation with the right. There are many examples among animals, however, of hemispheric asymmetry during slow-wave sleep. Marine mammals exhibit it, Sasaki said, presumably because they regularly need to resurface to breathe, even during sleep.
Now it’s been found in humans as a first-night phenomenon.
Website: F. Mansfield, 2015
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