Strangely, they found that the sleeping brains showed asymmetrical patterns of sleep activity, with one hemisphere humming along while the other slept. And while the sprightly hemisphere wasn’t fully awake, it was much more active than the other—even responsive to external stimuli. Subjects in the study experiencing FNE, for example, were jolted awake by “deviant” sounds. A creaking door perhaps. Or a shrieking animal. For most of the subjects, the night watchman hemisphere of their brain was the left side, for inexplicable reasons.