Instability of brain connectivity during nonrapid eye movement sleep reflects altered properties of information integration.
Human Brain Mapping August 1, 2019 Yi-Chia Kung, Chia-Wei Li, Shuo Chen et al.
During nonrapid eye movement (NREM) sleep, consciousness fades as the brain's dynamic functional connectivity changes. Using simultaneous EEG-fMRI recordings in 12 healthy men, the study examined two aspects of dynamic connectivity: mean (dFCmean), reflecting stable network integrity, and variance (dFCvar), indicating instability of information transfer. As sleep deepened, dFCmean decreased progressively across waking and NREM stages (N0~N1 > N2 > N3), while dFCvar peaked during N2 stage (N0~N1 < N3 < N2), suggesting unstable whole-brain synchronizations. In N3 stage, overall network integration was disrupted, with lowest dFCmean and elevated dFCvar. The findings suggest that consciousness dissipates when network specificity breaks down alongside increasing variability of information exchange.