Why is the first night somewhere new so light?

There is an old saying in Japan: change your pillow and you won’t sleep. Anyone who has lain awake in a hotel, in a new flat just before starting a new job, or at a parent’s house knows roughly what it means. In 2016, a team at Brown University went looking for what the brain is actually doing on that first night.

Sleep labs had already noticed the problem

The first-night effect isn’t a new idea. People often sleep noticeably worse on their first night in an unfamiliar place, and sleep labs see it so reliably that studies usually build in an “adaptation night” and leave its data out. The Brown team, led by Masako Tamaki with Yuka Sasaki as corresponding author, did the opposite. They made that first night the thing they measured.

Over three experiments, 35 volunteers slept in the lab for two sessions a week apart. The researchers combined standard sleep recordings with brain imaging (EEG, MEG and MRI), which let them compare the left and right halves of the brain during sleep in unusual detail.

What the Brown team found in 2016

One half of the brain slept less deeply than the other. During slow-wave sleep, the deepest stage, a network in the left hemisphere showed shallower sleep than the same network on the right. This was the default-mode network, a set of regions usually linked with mind-wandering and inward thought when we’re awake and resting. The three other networks the team checked showed no such difference, and neither did the other sleep stages.

The imbalance also tracked how the night went. In the paper’s words, the degree of asymmetry “was significantly correlated with the sleep-onset latency”, which simply means the time it took people to fall asleep. The bigger the gap between the two sides, the longer people took to drift off.

The lighter side listened harder

This is where sound comes in. While the volunteers were in deep sleep, the researchers played a steady run of beeps with occasional irregular ones mixed in, sending them to one ear or the other. Each ear feeds mainly into the opposite side of the brain, so sound in the right ear mostly reached the left hemisphere.

When the irregular beeps went to the right ear, toward the lighter-sleeping left side, people were more likely to wake and responded faster once awake. The same beeps in the left ear had less effect. The lighter half was not just sleeping less deeply. It was also picking up unexpected sounds more readily.

	First session	Second session, a week later
Deep sleep in the left default-mode network	Shallower than on the right	No significant difference
Response to irregular beeps	More arousals and faster responses via the left side	Imbalance not seen

The authors describe it as a kind of “night watch to protect ourselves” in a place the brain hasn’t yet judged safe. Some animals show something similar. Sasaki pointed to marine mammals, which keep one hemisphere more awake during deep sleep, presumably because they need to surface to breathe.

Limits: what the study leaves open

The research is careful and the questions it couldn’t answer are worth knowing too.

• Only the first stretch of deep sleep was measured. Nobody knows yet whether the left side keeps watch all night or swaps shifts with the right later on. Sasaki said it is possible that the watchful hemisphere alternates.
• Only four brain networks were checked. The default-mode network may be working with others the team didn’t look at.
• It was a lab, not a hotel. The volunteers were screened before taking part so their usual sleep was likely to be typical, and in surveys they didn’t report unusual discomfort or anxiety. Daily life is messier.
• Nothing was tested to reduce the effect. The study described the first night. It did not try any sound, routine or product to change it.

You can read the full paper through PubMed Central, or the plain-language summary on ScienceDaily. This post is a summary of that research and isn’t medical advice. If sleep is regularly hard for you, whether you’re at home or away, a doctor is the right person to talk to.

So what does this mean for a stay away from home?

For a traveller, someone settling in before a first day at work, or someone staying with a parent who needs them, the main takeaway is reassuring. A light, wakeful first night in a new place is common enough that sleep scientists have to plan around it. In this study it showed up on the first session and was gone by the second, a week later.

Some people like to bring a familiar sound with them, such as the fan setting they use at home, a steady noise, or a recording they know well. The study didn’t test whether that changes anything, so think of it as a comfort some people choose rather than a fix. What the research does show is that on a first night, part of the brain is listening a little harder than usual, and an unexpected sound is more likely to reach it.

Sources

1. Tamaki, M., Bang, J. W., Watanabe, T., & Sasaki, Y. (2016). “Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans.” Current Biology, 26(9), 1190–1194. https://doi.org/10.1016/j.cub.2016.02.063 (open full text: https://pmc.ncbi.nlm.nih.gov/articles/PMC4864126/)
2. Brown University (2016, April 21). “Asleep somewhere new, one brain hemisphere keeps watch” [summary]. ScienceDaily. https://www.sciencedaily.com/releases/2016/04/160421133630.htm