Your first night sleeping in a new place – in a hotel room, for example – will often end up a bad night’s sleep. According to a new study, this is because half your brain stays alert to keep you protected.
The “first-night effect” refers to the phenomenon in which new surrounds interrupt our normal sleeping patterns. This has long been acknowledged – in fact, most lab analyses that involve sleep will discount the first night, because the results tend to be so skewed.
This isn’t just a coincidence, according to researchers at Brown University – it’s actually your brain staying vigilant on night-watch in order to keep you safe.
Masako Tamaki and collagues performed a series of tests on the brain to figure out why these interruptions occur.
They watched brain activity by using ultra-sensitive neuroimaging, and discovered that half of each participant’s brain – specifically, the left hemisphere – remained active during sleep on the first night in the lab.
“In Japan they say, ‘if you change your pillow, you can’t sleep’,” says psychologist Yuka Sasaki and co-author of the paper. “You don’t sleep very well in a new place. We all know about it.”
The experiment was repeated three times. Each time, across all subjects, the results were the same.
To test for alertness, the researchers played sounds into each ear of the sleeping participants and found that when sounds were administered into the right ear – that is, stimulating the left side of the brain – participants were more likely to wake from sleep.
This suggests the brain activity is for increased alertness, which may be more necessary in unfamiliar surroundings. Or, according to the paper, that “troubled sleep in an unfamiliar environment is an act for survival over an unfamiliar and potentially dangerous environment by keeping one hemisphere partially more vigilant than the other hemisphere as a night watch.”
According to the findings, published in Current Biology, by the second night, there was no difference in activity levels between the hemispheres of the brain.
The researchers only studied early sleep phases, so they’re still unsure as to whether the left side of the brain stays alert throughout the entire first night, or switches to give the right side a go.
“It is possible that that the surveillance hemisphere may alternate,” says Sasaki.
This hemispheric switching – known as interhemispheric asymmetry – is fairly common in the animal world, particularly in marine mammals, who need to breathe regularly even during sleep.