Sub-narrow band sleep stage analysis — eigenvalues and eigenvectors of the multi-band cross-correlation matrix

Here we present an analysis of eigenvalues and eigenvectors of a correlation matrix that contains intra- and inter-frequency band correlations for narrow band filtered EEG signals of healthy subjects during sleep. We find that inter-band correlations of the same electrode are particularly suitable for distinguishing different sleep stages. However, largest eigenvalues and their corresponding eigenvectors show an extremely stable behavior during night sleep, while sleep stages manifest via specific deviations from an overall stable structure expressed by relative eigenvalues and deviations from average eigenvectors. Concluding that valuable information is encoded along the whole spectrum of eigenvalues and eigenvectors of the correlation matrix, we interpret our results in term of dynamical system theory.