EEG Connectivity is an Objective Signature of Reduced Consciousness and Sleep Depth
Brain Topography September 5, 2025 Toedt Inken, Gesine Hermann, Enzo Tagliazucchi et al.
Consciousness levels vary across human sleep stages. This study tested whether functional connectivity (FC) between distant brain regions, measured via electroencephalography (EEG) phase coupling, reflects sleep stages and thus changes in consciousness. In 14 participants undergoing all stages of non-rapid eye movement (NREM) sleep, six phase coupling metrics were computed. Alpha-band coupling decreased from wakefulness to sleep stages N1 and N2, while delta-band coupling increased in deep sleep (N3). A classifier using FC features achieved up to 73% accuracy in distinguishing sleep stages. Distributed alpha-band phase patterns were most important for classification, supporting the hypothesis that long-range phase coupling, especially in the alpha band, is an electrophysiological correlate of consciousness across sleep stages.