Paradoxes of the first-night effect: a quantitative analysis of antero-posterior EEG topography

Objective: The first-night effect (FNE) is a common issue in sleep research. Being considered fragmented and poorly efficient, the adaptation night is discarded for data analysis. The present study aims to provide a quantitative and topographical EEG analysis of this phenomenon. Methods: Eight healthy subjects slept for two consecutive nights (adaptation (AD) and baseline (BSL)), and their polysomnography was visually scored and then submitted to spectral power analysis. Results: The results showed a decreased quality and quantity of first-night sleep as indicated by more stage 1 and intrasleep wake, paralleled by a reduced sleep efficiency and a longer sleep onset latency. On the other hand, EEG quantitative data showed a more complex and apparently paradoxical picture. An increase in delta power was observed, particularly over the central areas during the first night, paralleled by an increased power in beta bin frequencies solely at posterior scalp locations. Conclusions: These results have been interpreted as caused by, respectively, a reduced total sleep time during the adaptation night and a cortical hyperactivity, typical of psychophysiological insomnia. The present results confirm the need to exclude the laboratory sleep adaptation night from data analysis since it is not a reliable index of sleep on subsequent nights as regards both visual scoring and quantitative EEG analysis. Finally, regional differences between REM and NREM sleep have been confirmed. Significance: This is the first attempt to evaluate the FNE with a quantitative approach to the antero-posterior EEG topography, providing both a Hz-by-Hz and a classical EEG band-based analysis.