User:Niveettha

The first night effect corresponds to an abnormal sleep rhythm experienced in a non-familiar environment. Researchers found out that subjects need adaptation before having regular sleep in an unknown place. Indeed, compared to the following nights, the first night reports longer sleep onset latency, lower sleep efficiency, longer REM latency and decreased REM. Due to these anomalies, the data of the first night spent in the laboratory is often not taken into account by researchers: the continuous awakenings and the high number of sleep-stage changes suggest that subjects are more in an awake condition rather than sleeping.

Higher activity of a more vigilant hemisphere leads to the first night effect. The association between the interhemispheric asymmetry in deep sleep and the effect of the first night is identified in the default mode network. The degree of asymmetry is significantly correlated to the sleep onset, which shows the first night effect. Furthermore, the hemisphere experiencing reduced sleep shows reactions to deviant external stimuli by generating more rapid behavioral responses compared to the other hemisphere. These asymmetries do not persist in the following sessions of sleep. These findings can be associated with the survival law: the hemisphere resulting more active and vigilant while sleeping in an unfamiliar situation enables a more rapid reaction if external stimuli are perceived. Therefore, it can be assumed that the first night effect is involved in sleeping as a protective mechanism.