Abstract
There are prominent individual differences in sleep patterns and some of these can be observed within the EEG. In order to determine whether the EEG can effectively serve as a biomarker for individual differences and in order to establish whether such differences constituted trait-like individual differences, we assessed the stability and robustness of sleep and the sleep EEG in physiological and pharmacological studies. The spectral composition of the EEG and PSG derived sleep measures were assessed for traitlike inter-individual variability by calculating ICCs in 1) a study investigating the effects of sleep extension, sleep restriction and total sleep deprivation on sleep and the EEG and the contribution of the PER3 polymorphism to individual differences 2) a study investigating the effects of polychromatic light mixtures on the EEG and 3) a study investigating the effects of prolonged-release melatonin, temazepam and zolpidem on sleep and the EEG. Absolute power density values derived from the spectral composition of the EEG were particularly stable and robust and the ICCs were rated as ‘moderate’ to ‘almost perfect’ for NREM and REM sleep across the studies. ICCs for PSG measures were more variable. ICCs were also calculated on relative data in order to assess the stability and robustness of the response to sleep-wake manipulations in the first study; however, these ICCs were very low in comparison to those obtained for absolute data. The PER3 polymorphism differentially affected the some PSG measures and the EEG in our study population. In conclusion, we have provided further evidence for trait-like individual differences within sleep and the EEG, and as such the EEG does effectively serve as a biomarker for individual differences. However, whether these individual differences relate only to phenomena of the EEG or whether they relate to individual differences in sleep-wake regulation needs further investigation.