Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans
From their paper
In Brief Tamaki et al. find that when humans sleep in a novel environment, the default-mode network in one hemisphere is kept more vigilant to wake the sleeper up as a night watch upon detection of deviant stimuli. The regional interhemispheric asymmetric sleep in a novel environment may play a similar protective role to that in marine mammals and birds.
Paper here http://www.cell.com/current-biology/abstract/S0960-9822(16)30174-9