Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans.
Level 3 - non-randomized controlled study
Within-subject repeated-measures laboratory study; graded by design analogy for non-clinical physiological research.
PubMed 27112296 · doi:10.1016/j.cub.2016.02.063
What was done
Human sleep was evaluated across experimental sleep sessions to determine the neural basis of the first-night effect. Using advanced neuroimaging and polysomnography, researchers measured interhemispheric sleep depth, default-mode network activity, sleep-onset latency, and evoked neural and behavioral arousal responses to deviant external stimuli during the initial sleep session compared to subsequent sessions.
What was found
The abstract reports no numerical values, exact effect sizes, or p-values. Qualitatively, the first sleep session exhibited regional interhemispheric asymmetry of sleep depth within the default-mode network. The degree of this asymmetry was significantly correlated with sleep-onset latency. The hemisphere with shallower sleep displayed enhanced evoked brain responses to deviant external stimuli, resulting in more arousals and faster behavioral responses. None of these interhemispheric asymmetries were observed during subsequent sleep sessions.
Why it matters
This study provides evidence that the first-night effect operates as a regional unihemispheric vigilance system, functioning like a night watch to monitor unfamiliar surroundings during sleep.
Limits
The abstract does not disclose the sample size, participant demographics, or quantitative metrics. The findings reflect short-term laboratory adaptation, and it was not established whether hemisphere-specific vigilance alternates over time or applies to diverse real-world sleeping environments.
Cited by
- supports Sleeping in a new environment triggers the 'first night effect', which impairs sleep quality.