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.
Meditation produces a distinct, reversible mental state that reorganizes brain network hubs and connections without altering global network properties like small-worldness. Analyzing resting-state fMRI data from 18 Taoist meditators of varying expertise, the study found that during meditation, sensory cortex areas (primary visual and auditory cortices, temporopolar areas) showed decreased connectivity, while the thalamus and default mode network components (precuneus, posterior cingulate cortex) increased connectivity. Long-distance front-to-back connections increased, while right-left connections between homologous cortices decreased. These changes suggest that shifts in consciousness involve both topological and spatial reorganization of brain networks, with the anatomical pattern of integration being as important as its overall level.