Instability of brain connectivity during nonrapid eye movement sleep reflects altered properties of information integration.
Yi-Chia Kung, Chia-Wei Li, Shuo Chen, Sharon Chia-Ju Chen, Chun-Yi Z Lo, Timothy Lane, Bharat B. Biswal, Changwei W Wu, Ching-Po Lin
Human Brain Mapping August 1, 2019 DOI: 10.1002/hbm.24590 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Observational cohort Peer reviewed |
|---|---|
| Sample size | 12 |
| Population | Healthy men |
| Keywords | Consciousness Dynamic functional connectivity Sleep |
| Key findings | As sleep deepened, mean dynamic functional connectivity decreased progressively, while variance peaked during N2 stage, indicating that consciousness dissipates when network specificity breaks down with increasing variability of information exchange. |
Abstract
Nonrapid eye movement (NREM) sleep is associated with fading consciousness in humans. Recent neuroimaging studies have demonstrated the spatiotemporal alterations of the brain functional connectivity (FC) in NREM sleep, suggesting the changes of information integration in the sleeping brain. However, the common stationarity assumption in FC does not satisfactorily explain the dynamic process of information integration during sleep. The dynamic FC (dFC) across brain networks is speculated to better reflect the time-varying information propagation during sleep. Accordingly, we conducted simultaneous EEG-fMRI recordings involving 12 healthy men during sleep and observed dFC across sleep stages using the sliding-window approach. We divided dFC into two aspects: mean dFC (dFCmean ) and variance dFC (dFCvar ). A high dFCmean indicates stable brain network integrity, whereas a high dFCvar indicates instability of information transfer within and between functional networks. For the network-based dFC, the dFCvar were negatively correlated with the dFCmean across the waking and three NREM sleep stages. As sleep deepened, the dFCmean decreased (N0~N1 > N2 > N3), whereas the dFCvar peaked during the N2 stage (N0~N1 < N3 < N2). The highest dFCvar during the N2 stage indicated the unstable synchronizations across the entire brain. In the N3 stage, the overall disrupted network integration was observed through the lowest dFCmean and elevated dFCvar, compared with N0 and N1. Conclusively, when the network specificity (dFCmean ) breaks down, the consciousness dissipates with increasing variability of information exchange (dFCvar ).