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

Abstract

The first night in an unfamiliar environment is marked by reduced sleep quality and changes in sleep architecture. This so-called first-night effect (FNE) is well established for two consecutive nights and lays the foundation for including an adaptation night in sleep research to counteract FNEs. However, adaptation nights rarely happen immediately before experimental nights, which raises the question of how sleep adapts over nonconsecutive nights. Furthermore, it is yet unclear, how environmental familiarity and hemispheric asymmetry of slow-wave sleep (SWS) contribute to the explanation of FNEs. To address this gap, 45 healthy participants spent two weekly separated nights in the sleep laboratory. In a separate study, we investigated the influence of environmental familiarity on 30 participants who spent two nonconsecutive nights in the sleep laboratory and two nights at home. Sleep was recorded by polysomnography. Results of both studies show that FNEs also occur in nonconsecutive nights, particularly affecting wake after sleep onset, sleep onset latency, and total sleep time. Sleep disturbances in the first night happen in both familiar and unfamiliar environments. The degree of asymmetric SWS was not correlated with the FNE but rather tended to vary over the course of several nights. Our findings suggest that nonconsecutive adaptation nights are effective in controlling for FNEs, justifying the current practice in basic sleep research. Further research should focus on trait- and fluctuating state-like components explaining interhemispheric asymmetries.

Keywords: EEG analysis; asymmetry; electrophysiology; environment; first-night effect; polysomnography; sleep quality; sleep/wake cognition.

Graphical Abstract

Figure 1.

(a) Study design of Study 1: the study consisted of two nights, each separated by 1 week. In all nights, participants slept in the sleep laboratory. (b) Study design of Study 2: the study consisted of four nights, each separated by a 1-week interval. Half of the participants slept first in the sleep laboratory for two nights and then two nights at home or vice versa. The order was randomized and counterbalanced between the participants.

Figure 2.

Sleep parameters during both nights of Study 1 in the sleep laboratory. (a) Sleep onset latency (SOL). (b) Slow-wave sleep (SWS). (c) Rapid eye movement (REM) sleep. (d) Wake after sleep onset (WASO). (e) Total sleep time (TST). (f) Asymmetry index (AI) during SWS within the first sleep cycle. Data are means ± SEM. Numbers indicate absolute or relative values.

Figure 3.

Sleep parameters in familiar (Home) vs. unfamiliar (Lab) environment of Study 2. (a) Sleep onset latency (SOL). (b) Slow-wave sleep (SWS). (c) Wake after sleep onset (WASO). (d) Asymmetry index (AI) during SWS within the first sleep cycle. Data are means ± SEM. Numbers indicate absolute or relative values.

Figure 4.

Sleep parameters in the unfamiliar (Lab) environment of Study 2, separated by Home adaptation vs. No home adaptation group. (a) Sleep onset latency (SOL). (b) Slow-wave sleep (SWS). (c) Rapid eye movement (REM) sleep. (d) Wake after sleep onset (WASO). (e) Total sleep time (TST). (f) Asymmetry index (AI) during SWS within the first sleep cycle. Data are means ± SEM. Numbers indicate absolute or relative values.