It’s safe to say that more or less everyone has experience with feeling slightly under the weather after the first night sleeping in an unfamiliar bed. Curiously enough, though, for most people, the effect simply vanishes on the second or third night.
Known as the First Night Effect (FNE) to psychologists, who discovered it in the lab many decades ago, this phenomenon remained a bit of a puzzle. Now, a group of researchers, led by Yuka Sasaki from Brown University, suggests it all comes down to our brain retaining some its daytime vigilance when faced with novel surroundings at night.
Observed in some birds and mammals, the ability to sleep with only one hemisphere of the brain at a time was never before seen in humans. Given the evolutionary implications of it, however, it’s hardly all that surprising.
In the study, published Thursday in the journal Current Biology, the researchers looked at the brain wave patterns of 35 Brown University students who slept in the alien environment of the University’s Department of Psychological Sciences.
The team measured something called slow-wave activity, which appears during deep sleep. And they found that some areas of the left hemisphere were significantly more active than the corresponding areas of the right hemisphere.
To confirm that the left side of the brain really is more alert, Sasaki’s team carried out two further experiments. First, they had sleeping students listen to a mix of regularly timed beeps of the same tone followed by beeps of a different tone.
The hypothesis was that if the left hemisphere remains more alert to potential nocturnal dangers in a new location, it should react to the beeps that stand out – which is exactly what happened.
Then they played a sound loud enough to rouse someone who was sleeping lightly, again with positive results. They also found that playing it in the right ear, which is connected to the left hemisphere, woke the students even faster.
“When we’re sleeping in a new environment and we don’t know how many predators are around,” said sleep researcher Niels Rattenborg who was not involved in the study, “it would make sense to keep half the brain more alert and more responsive to bumps in the night.”
Unfortunately, there isn’t much we can about the way our “monkey brains” respond, leaving us with the next best thing – lots of coffee during the hazy days of sleeping in strange places.