0089 Examination of Post-arousal Hypersynchrony in the First-night Effect

Abstract Introduction The first-night effect (FNE) is a sleep disturbance caused by sleeping in a new environment. FNE observed on polysomnography includes increased wakefulness and sleep instability. Post-arousal hypersynchrony (PAH) is an arousal subtype with a post-arousal delta wave burst that antagonizes arousal and maintains sleep (Suzuki et al., 2021). Furthermore, we have shown that PAH correlates with the number of arousals; increased arousals increases PAH. Therefore, we hypothesized that the FNE would increase arousal and PAH. Methods Fifteen healthy adults (five women, mean ± standard deviation 21.7 ± 1.6 years) undergoing first-time polysomnography were included. After three days of sleep-wake cycle control before measurement, four nights of polysomnography were performed in the laboratory. A registered polysomnographic technologist blindly scored the participants’ sleep stages and analyzed PAH. Linear mixed models and non-parametric tests were performed on sleep variables and PAH for changes from the first to fourth measurement night. Results Sleep variables did not change significantly with the number of measurements. Contrary to our hypothesis, there was no FNE on the number of arousals. The number of PAH had a significant main effect on the number of measurements, showing a significant decrease on the fourth night compared to the first night. Conclusion Sleep variables, including arousal, were not affected by the FNE, whereas PAH was. The lack of a FNE on the sleep variables may be due to a ceiling effect caused by sleep in young healthy adults. Since the number of arousals showed no changes, the FNE of PAH could not be explained regarding inhibition on arousal, such as a role in sleep maintenance. The decreased number of PAH sleep measurements may indicate sleep stabilization. Support (if any) This study was supported by JSPS KAKENHI under grant number JP 23K14436 and Japan Agency for Medical Research and Development under grant number JP21zf0127005.