Abstract
Difficulty sleeping in a novel environment is a common phenomenon that is often described as the first night effect (FNE). Previous works have found FNE on sleep architecture and sleep power spectra parameters, especially during non-rapid eye movement (NREM) sleep. However, the impact of FNE on sleep parameters, including local differences in electroencephalographic (EEG) activity across nights, has not been systematically assessed. Here, we performed high-density EEG sleep recordings on 27 healthy individuals on two nights and examined differences in sleep architecture, NREM (stages 2 and 3) EEG power spectra, and NREM power topography across nights. We found higher wakefulness after sleep onset (WASO), reduced sleep efficiency, and less deep NREM sleep (stage 3), along with increased high-frequency NREM EEG power during the first night of sleep, corresponding to small to medium effect sizes (Cohen’s d ≤ 0.5). Furthermore, study individuals showed significantly lower slow-wave activity in right frontal/prefrontal regions as well as higher sigma and beta activities in medial and left frontal/prefrontal areas, yielding medium to large effect sizes (Cohen’s d ≥ 0.5). Altogether, these findings suggest the FNE is characterized by less efficient, more fragmented, shallower sleep that tends to affect especially certain brain regions. The magnitude and specificity of these effects should be considered when designing sleep studies aiming to compare across night effects.
Highlights
Adaptation nights are commonly implemented in sleep studies to counter differences in baseline sleep data caused by environmental factors
Study participants showed decreased sleep efficiency (p = 0.020, effect size = −0.5), reduced non-rapid eye movement (NREM) stage N3 sleep, called slow-wave sleep (p = 0.033, effect size = −0.4), and increased waking after sleep onset (WASO, p = 0.018, effect size = 0.5) during the first night compared to the second night of sleep
We found no across night difference in any of the other sleep architecture parameters, including total sleep time, sleep latency, and time spent in REM sleep
Summary
Adaptation nights are commonly implemented in sleep studies to counter differences in baseline sleep data caused by environmental factors One of these environmental factors is the first night effect (FNE). In addition to sleep architecture, some studies have examined FNE on sleep EEG activity, especially during the deepest stages of NREM sleep (stage 3; N3), referred to as slow-wave sleep (SWS) [8]. Higher spectral power within alpha and beta bands was observed in SWS during the first night relative to the second night in healthy individuals [11]. Another sleep study reported that theta and sigma NREM sleep EEG activity tended to be lower on the first night of sleep compared to the following nights [12]
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