The first-night effect of sleep occurs over nonconsecutive nights in unfamiliar and familiar environments

Interviewer: This research is focused on sleep changes in a different environment. What is the FNE phenomenon?

Anna Wick : The First-Night Effect (FNE) is a well-documented phenomenon characterized by disrupted sleep quality during the first night spent in an unfamiliar environment. On this night, individuals typically experience longer sleep onset latency (SOL), increased wake time after sleep onset (WASO), and delayed onset of REM sleep. These disturbances are accompanied by shorter total sleep time (TST), lower sleep efficiency, reduced REM sleep, and an increase in stage 1 non-REM (N1) sleep compared to subsequent nights. To account for the FNE, sleep researchers commonly include an adaptation night prior to the experimental night. Data collected during the adaptation night are excluded from analysis to ensure that the recorded sleep patterns more accurately reflect the participant’s typical sleep architecture¹.

Interviewer: Which research questions were addressed in this study? Could you describe the aim of your study and main objectives?

Anna Wick: In sleep research, adaptation nights are typically not scheduled immediately before the experimental night. Furthermore, a previous study demonstrated that during the first night in an unfamiliar environment, one brain hemisphere shows reduced slow-wave activity (SWA) during slow-wave sleep (SWS) compared to the other. This asymmetric activity was correlated with an FNE. The researchers interpreted this as a protective mechanism, with one hemisphere remaining more alert in unfamiliar environments².

In our study, we aimed to investigate whether a FNE reoccurs in sleep studies with non-consecutive weekly adaptation nights and whether or not FNEs in a familiar environment differ from those in an unfamiliar environment. Moreover, we aimed to investigate how environmental familiarity affects the adaptation process and the hemispheric asymmetry of SWS.

Interviewer: Could you describe the main outcomes?

Anna Wick: The results of both studies show that FNE can also occur on non-consecutive nights, particularly affecting WASO, SOL, and TST. Interestingly, although sleep was generally better in the familiar environment, we observed sleep disturbances during the first night in both familiar and unfamiliar environments. Interestingly, the degree of asymmetric SWS was not directly associated with the FNE but rather fluctuated across the nights, suggesting it may be influenced by other factors than environmental unfamiliarity.

Interviewer: What are the implications of these findings, and which future perspectives could this study disclose?

Anna Wick: Our findings suggest that non-consecutive adaptation nights are effective in controlling for the FNE, supporting the validity of current practices in basic sleep research. These results reinforce the importance of accounting for adaptation effects even when experimental nights are not scheduled consecutively.

For future research, we recommend investigating both trait-like and state-dependent factors that may contribute to interhemispheric asymmetries SWS. Understanding these underlying mechanisms could provide deeper insight into individual differences asymmetric SWA and environmental responsiveness.

Sources:

1. Ding, L., Chen, B., Dai, Y., & Li, Y. (2022). A meta-analysis of the first-night effect in healthy individuals for the full age spectrum. Sleep Medicine, 89, 159-165.
2. Tamaki, M., Bang, J. W., Watanabe, T., & Sasaki, Y. (2016). Night watch in one brain hemisphere during sleep associated with the first-night effect in humans. Current biology, 26(9), 1190-1194.