You collapse into a hotel bed after a long day, exhausted, and still spend hours staring at an unfamiliar ceiling. Sleep researchers call this the first-night effect, and it is one of the most consistent findings in laboratory sleep studies. Most people take longer to fall asleep, wake more often, and get less deep sleep on the first night in a new environment.
A study published in Current Biology in April 2016 helped explain why. Researchers at Brown University measured brain activity across two nights, one week apart, in 35 volunteers using EEG, MEG, and MRI.
On the first night, the default-mode network in the left hemisphere stayed more active than the right during deep, slow-wave sleep. Sounds played into the right ear, which stimulate the left hemisphere, were more likely to wake sleepers than sounds played into the left ear. By the second night, that asymmetry had disappeared.
Half the brain acts as a night watch
The pattern looks like a scaled-down version of what marine mammals and some birds do routinely. Dolphins and certain waterbirds can sleep with one hemisphere at a time, keeping the other awake to watch for predators. Humans do not go that far, but the Brown team argued that our left hemisphere partially plays that role on night one.
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"In Japan they say, if you change your pillow, you can't sleep. You don't sleep very well in a new place," said Yuka Sasaki, research associate professor of cognitive linguistic and psychological sciences at Brown, in the university's announcement of the findings.
A follow-up study by Masako Tamaki and Sasaki, published in Frontiers in Neuroscience in October 2019, suggests the surveillance system also shows up in REM sleep, though without the same left-right split.
In that experiment, sleep onset latency was 11.6 minutes on day one versus 5.2 minutes on day two, and brain responses to sounds during REM showed heightened vigilance on the first night, engaging both hemispheres rather than one.
How long it really lasts
The classic view is that the effect fades after one night, but the picture is more nuanced. Some sleep research has found that variables tied to REM sleep can take several nights to fully stabilize, meaning the underlying adaptation is not always over by morning two.
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For most travelers, though, the sharpest disruption is on night one. Writing in The Conversation in February 2026, sleep researcher Charlotte Gupta of CQUniversity Australia and Dayna Easton of Flinders University note that even positive stress, like excitement about a trip, activates the same arousal systems as negative stress, and arousal and sleep act as competitors in the brain.
What actually helps on night one
You cannot switch off an evolutionary alarm system, but you can give your brain more familiar signals to work with. Guidance from the Sleep Foundation points to a small set of practical moves.
Pack sensory cues from home. A favorite pillowcase, an eye mask, or a fragrance you already associate with bedtime can nudge the brain toward recognition. A photograph on the nightstand serves the same purpose.
Manage the room itself. Aim for a cool temperature, ideally between 60 and 67 degrees Fahrenheit, and block light with an eye mask or the room's blackout curtains. A white noise machine, an app, or simple earplugs can mask the clangs of an unfamiliar hallway.
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Protect the wind-down. Keep the last hour before bed dim and screen-light. Hold to the same pre-sleep routine you use at home, whether that is reading, stretching, or a short breathing exercise. If a big event is on day two, arriving a day earlier gives the brain a night to log the room as safe before the sleep that really counts.
If persistent sleep problems follow you home from the road, a conversation with your doctor is a better next step than another sleep gadget.
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