Can spectral power predict subjective sleep quality in healthy individuals?

The aim of this study was to assess the relationship between electroencephalogram (EEG) power spectral density and subjective sleep quality in healthy individuals. The sample was selected from the archival database of the Sleep Center at the Department for Psychiatry and Psychotherapy, Medical Center - University of Freiburg, and consisted of 206 healthy adults aged 19-73 years (85 male, 121 female) who underwent a polysomnographic examination for two consecutive nights. A multivariate analysis of variance (MANOVA) with spectral power variables of different frequency bands as dependent variables and subjective sleep quality, night number, age and gender as independent variables was statistically significant for subjective sleep quality, age and gender, but not for night number. In subsequent separate ANOVAs, higher subjective sleep quality was significantly related to decreased non-rapid eye movement (NREM) stage 2 sigma 2 and rapid eye movement (REM) delta 1; however, the relation between REM delta 1 and sleep quality did not remain significant when REM duration was accounted for. The effect sizes of the correlations between sleep quality and spectral power were small (r = -0.1). In contrast to common assumptions, the amount of variance in subjective sleep quality that can be explained through EEG power spectral density variables is small. This finding indicates that subjective and objective sleep are different constructs, the interrelations of which are not yet well understood.