Scientists explain what underlies the "first-night effect," phenomenon that poses an inconvenience to business travellers and sleep researchers. Sleep is often noticeably worse during the first night in, say, a hotel or a sleep lab.
"In Japan they say, 'if you change your pillow, you cannot sleep.' You do not sleep very well in a new place. We all know about it," said Yuka Sasaki from Brown University in the US.
They consistently found that on the first night in the lab, a particular network in the left hemisphere remained more active than in the right hemisphere, specifically during a deep sleep phase known as "slow-wave" sleep.
When researchers stimulated the left hemisphere with irregular beeping sounds (played in the right ear), that prompted a significantly greater likelihood of waking, and faster action upon waking, than if sounds were played in to the left ear to stimulate the right hemisphere.
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On the second night of sleep there was no significant difference between left and right hemispheres even in the "default-mode network" of the left hemisphere, which does make a difference on the first night.
The testing, in other words, pinpointed a first-night-only effect specifically in the default-mode network of the left hemisphere during the slow-wave phase.
For the study, researchers used electroencephalography, magnetoencephelography, and magnetic resonance imaging to make unusually high-resolution and sensitive measurements with wide brain coverage.