Robert Bodizs, PhD
Institute of Behavioural Sciences
Semmelweis University
Budapest, Hungary
Sleep is an inherent feature of human neurobehavioral functioning, providing the fine-tuning and optimization of several cognitive, emotional and health-related regulatory processes. However, clinical and research practices largely rely on consensual criteria of sleep-wake characterization the latter finding its roots in a technologically outdated, paper era of polysomnography. In turn, quantitative EEG measures were shown to be largely redundant and non-standardizable. We aim to transcend this issue by relying on a restricted set of composite EEG measures of NREM sleep EEG based on the power law scaling of the Fourier spectra (scale-free and oscillatory measures). We hypothesize that spectral slopes are characterized by sufficient convergent and criterion validity in order to be considered as alternative and more standardizable measures of sleep intensity, whereas spectral peak frequencies reveal a U-shaped overnight distribution indicating putative circadian influences. Hypotheses were tested on the Budapest-Munich database of sleep records (N = 251 subjects, age range: 4-69 years). NREM sleep EEG spectra was parametrized by using a previously published method (excluding spectral peak regions, fitting, deriving peak parameters). Findings indicate that spectral slopes flatten over successive sleep cycles, reproduce known age and region-effects, correlating reliably with slow wave activity (SWA). Furthermore, its interindividual variability was proven to be less than of the SWA. Frequency of the largest peak was shown to roughly correspond to spindle frequency as the known age, sex, and regional effects were evident. Besides, the peak frequencies in the frontopolar region were compatible with an assumed circadian modulation. In conclusion, the appropriate parameterization of the NREM sleep EEG Fourier spectra can be a feasible approach in unravelling the fundamental sleep regulatory processes proposed in the two-process model of sleep regulation.