Structuring the inter-individual variation in waking EEG can help to discriminate between the objective markers of sleep debt and sleep pressure

Question of the study

Our aim was to assess the inter-individual link between the principal component structure of the waking EEG and the response of the parameters of sleep-wake regulation to sleep loss.

Subjects and methods

Resting EEG was recorded 9 times at 3-h intervals with eyes closed and open during the course of sustained wakefulness of 130 healthy subjects. The ipsatized power densities were calculated from the log-transformed absolute powers averaged across 10 frequency ranges (from slow delta to slow gamma). These spectra were further reduced by performing principal component analysis, which yielded the subjects’ scores on the largest principal components (PCs).

Results and conclusions

It was found that any EEG spectrum can be parsimoniously represented by only three scores on the PCs with eigenvalues greater or approximately equal to 1. These PCs remained virtually invariant in terms of the order of their extraction and loading patterns which signify EEG amplifying (1^st), EEG slowing (2^nd), and EEG smoothing (3^rd). In the course of wakefulness, the 1^st PC score was related to sleep debt (i.e., self-reported sleep restriction on the morning preceding the experiment), while the 2^nd PC score was associated with sleep pressure (i.e., sleepiness perceived during night sleep deprivation).