Like a pirate sleeping with one eye open, half of our brain stays awake when we sleep in a new place for the first time. If you ever had a rocky first night when on vacation, or if you’re a rock star on tour who never sleeps, or sleeps well, in the same bed twice, now you know why.
The phenomenon, known about for some time, is called First-Night Effect, or FNE, and researchers may have just figured out what causes it. Or at least how it works.
The researchers, from Brown University, hooked up their test subjects to various brain-monitoring devices while they slept. What they found was that, on the first night in the lab, half of the brain stayed awake (in most, but not all, cases, the left hemisphere). Specifically, during deep sleep, the "default-mode network" stayed active. This is a circuit in the brain that is active when we’re not engaged in a task—we may be day dreaming, or thinking about others or ourselves, for example.
The researchers found that when the default-mode network was switched on, subjects experienced more "arousals"—that is, they partially woke up more often. The researchers also played high-pitched beeps into the subjects’ ears. When they played them into the right ear (connected to the left side of the brain), they "prompted a significantly greater likelihood of waking, and faster action upon waking, than if sounds were played into the left ear to stimulate the right hemisphere."
The study only looked at the first phase of sleep, so it’s not know whether the brain stays awake the whole night, or if it switches between hemispheres throughout the night.
The obvious explanation is that the brain is keeping alert, even while we sleep, listening out for danger when we’re slumbering in unfamiliar territory, and we use a part of the brain that is used to idling along while the rest of the brain is at rest. Marine mammal and some birds use the same trick, say the researchers, but this kind of activity has never been reported in humans.
One of the authors, Yuki Sasaki, has some reassuring words for people who travel a lot, and may never spend more than one night in a new place. "Human's brains are very flexible," she said. "Thus, people who often are in new places may not necessarily have poor sleep on a regular basis."
The next stage for Sasaki and her team is to use something called "transcranial magnetic stimulation" to deactivate the wakeful circuit, to see if sleep can be improved. This might help frequent travelers, but it also sounds pretty scary, like the makings of the plot for an episode of Criminal Minds.