Do you ever wonder why you couldn’t get decent sleep when you’re in a new, unfamiliar territory?

On your first night in a new place, one brain hemisphere stays more alert than the other during deep-sleep stage as the former is gearing up for any threat or trouble, according to findings from Brown University researchers.

Through a unique experiment, the researchers sought to understand the so-called first-night effect, a common problem affecting frequent travelers and individuals spending their first night in new hotels or accommodations.

In three separate experiments, they employed different methods to measure brain activity during two nights of sleep – a week apart – among 35 subjects. The findings were consistent – on the first night in the sleep lab, a specific left-hemisphere network of the brain stayed more “alive” than the right, particularly during the “slow-wave” or deep sleep stage.

Study author Masako Tamaki explained that this is the deepest sleep phase where the so-called arousal threshold appears to be at its peak, which means it is harder to wake someone up from slow-wave sleep than during lighter stages.

“This suggests that people are vulnerable during slow-wave sleep, and this might be why we found interhemispheric asymmetry during this phase of sleep,” he told Gizmodo.

Results vouched for the first-night effect, as the team did not see the same brain asymmetry during follow-up sessions of sleep. They also pinpointed a left-hemisphere region known as the default-mode network, which is a range of cortical links instrumental in functions such as mind-wandering and introspection.

It remains unclear why the default-mode network stays alert, but it could be a function of night watching or preparing to promptly react to one’s environment.

“This half-asleep, half-awake state may work as a way to monitor unfamiliar surroundings,” added Tamaki.

The left hemisphere, too, appeared to have increased sound sensitivity. When the team used irregular beeping tunes in the right ear to stimulate this hemisphere, they induced a substantially greater chance of walking and quicker action, compared to when the sounds were played to stimulate the right hemisphere.

The first-night effect emerges as a function of the evolutionary process, where our ancestors were protected by the regional asymmetry. The trait has probably stuck with humans ever since.

Some questions remain however. Does the left hemisphere stay alert all night long, or does it work in shifts with the right? Is the default-mode network a lone watchman, or does it collaborate with other networks?

Co-author Yuka Sasaki said other animals exhibit this asymmetry during slow-wave sleep, including marine creatures that need to resurface in order to breathe – even as they sleep.

The researchers advised that while the first-night effect may be here to stay, there are steps to manage it, such as bringing a pillow to a new place for some comfort. Another trick is to avoid worrying too much, as it keeps the brain awake. It is recommended to spend at least two nights in a new place before an important occasion so as to enjoy quality shuteye.

The findings are published in the journal Current Biology.

Photo: Clare Bell | Flickr

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