Ever wonder why you don’t feel rested after sleeping the first night in a new place, such as a hotel room? It’s not surprising, of course, given the different bed, unfamiliar surroundings, and possibly residual agitation caused by travel.
Now researchers from Brown University, in a study in Current Biology, have offered another possible explanation for what they dubbed the “first-night effect”: One hemisphere of the brain may sleep less soundly in order to keep watch.
Using advanced imaging tests on the brains of 35 young adults in a sleep clinic, they found that the left side of the brain stayed more vigilant when sleeping, as seen by increased responsiveness to stimuli such as noise—but only the first night, not subsequent nights. The more trouble people had falling asleep, the greater the first-night asymmetry between the hemispheres.
Some birds and marine mammals experience “unilateral hemispheric” sleep, probably to stay alert for risks during sleep, the researchers pointed out. Their new findings suggest something similar in humans: “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.”
For tips about better sleep, see 15+ Sleep Remedies