NREM sleep stages specifically alter dynamical integration of large-scale brain networks

During non-rapid eye movement (NREM) sleep, the brain's large-scale functional networks show a surprising pattern: nearly all networks are most active during NREM stage 2, then abruptly lose activity in NREM stage 3. However, despite this high activity in stage 2, the functional connections and mutual dependencies between networks progressively break down as sleep deepens. This means that even though networks attempt to communicate during stage 2, the efficiency of information transfer is low. The findings advance neural models of sleep and consciousness by showing that network integrity, not just activity levels, is crucial for conscious awareness.

Study at a glance

Abstract

Summary: Functional dissociations in the brain observed during non-rapid eye movement (NREM) sleep have been associated with reduced information integration and impaired consciousness that accompany increasing sleep depth. Here, we explored the dynamical properties of large-scale functional brain networks derived from transient brain activity using functional magnetic resonance imaging. Spatial brain maps generally display significant modifications in terms of their tendency to occur across wakefulness and NREM sleep. Unexpectedly, almost all networks predominated in activity during NREM stage 2 before an abrupt loss of activity is observed in NREM stage 3. Yet, functional connectivity and mutual dependencies between these networks progressively broke down with increasing sleep depth. Thus, the efficiency of information transfer during NREM stage 2 is low despite the high attempt to communicate. Critically, our approach provides relevant data for evaluating functional brain network integrity and our findings robustly support a significant advance in our neural models of human sleep and consciousness.