During sleep, brain dynamics shift from wakefulness through NREM stages N1, N2, and N3, driven partly by decreases in the neuromodulators acetylcholine (ACh) and noradrenaline (NA). Analyzing fMRI data from healthy individuals and using a whole-brain model, the study shows that functional connectivity (FC) changes distinctly: locus coeruleus connectivity with the cortex decreases during N2 and N3, while basal forebrain connectivity with the cortex decreases during N3. Compared to wakefulness, the brain becomes more integrated in N1 and more segregated in N3. Region-specific neurotransmitter effects are key to explaining these FC changes, advancing understanding of how neurochemistry modulates sleep stages and consciousness transitions.
Disorders of consciousness are linked to large-scale changes in brain dynamics, but the structural factors behind these changes are unclear. Using a whole-brain computational model constrained by diffusion MRI-derived connectivity, the authors show that a node's integration within the structural connectome, measured by a spectral integration metric, strongly predicts its impact on global brain dynamics. Lesions to highly integrative hubs, especially in posterior medial regions like the precuneus and posterior cingulate cortex, drive the system toward low-complexity dynamical regimes resembling disorders of consciousness. Increasing excitability in these regions restores healthy-like dynamics in silico. Perturbations to weakly integrated regions have limited global effects, explaining why damage to specific hubs disproportionately disrupts conscious brain activity.