Associations Between EEG-Vigilance and the Autonomous Nervous System Activity During Rest

The temporal dynamics of electroencephalogram (EEG)-vigilance as a measure of tonic cortical arousal are discussed as pathogenetic factors in neuropsychiatric disorders. Although there is broad knowledge about the interaction of cortical arousal and activity of the autonomous nervous system (ANS) during different sleep stages, the association and temporal interaction between fine-graded EEG-vigilance stages and markers of sympathetic and parasympathetic activity during the transition from wakefulness to sleep onset warrants more detailed exploration and was focus of the presented study. A 15-min resting-EEG, electrocardiogram (ECG), and skin conductance level (SCL) were recorded from 54 healthy subjects. Using an EEG-algorithm (VIGALL), 1-s segments were classified into seven different vigilance stages. Associations and temporal interactions between EEG-vigilance stages and heart rate variability (HRV), heart rate (HR), and SCL were computed using correlation analysis, regression analysis, and cross-correlations of EEG-vigilance and ANS time series. EEG-vigilance stages and ANS activity showed a significant association between increased HRV parameters including total and (normalized) very low frequency power and low vigilance stages. Regression analysis revealed significantly increased values of SCL and HR for high vigilance stages in comparison to lower ones. In these relationships, for SCL but not HR most of the covariance was explained by the effect of time. Phasic increases in EEG-vigilance were paralleled by significant increases of HR but not of SCL. Cross-correlations between EEG-vigilance and ANS time series yielded highest correlations when there was no or only a minimal temporal lag. ANS activity during the transition from wakefulness to sleep onset gradually changes along with different fine-graded EEG-vigilance stages. Associations between cortical and autonomic activity are better reflected by HR than by SCL.