title: Hierarchical clustering of brain activity during human nonrapid eye movement sleep.
abstract: Consciousness is reduced during nonrapid eye movement (NREM) sleep due to changes in brain function that are still poorly understood. Here, we tested the hypothesis that impaired consciousness during NREM sleep is associated with an increased modularity of brain activity. Cerebral connectivity was quantified in resting-state functional magnetic resonance imaging times series acquired in 13 healthy volunteers during wakefulness and NREM sleep. The analysis revealed a modification of the hierarchical organization of large-scale networks into smaller independent modules during NREM sleep, independently from EEG markers of the slow oscillation. Such modifications in brain connectivity, possibly driven by sleep ultraslow oscillations, could hinder the brain's ability to integrate information and account for decreased consciousness during NREM sleep.
authors.affiliation: Cyclotron Research Centre,  University of Liège, 4000 Liège,  Belgium.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Boly
authors.forename: Vincent
authors.initials: V
authors.lastname: Perlbarg
authors.forename: Guillaume
authors.initials: G
authors.lastname: Marrelec
authors.forename: Manuel
authors.initials: M
authors.lastname: Schabus
authors.forename: Steven
authors.initials: S
authors.lastname: Laureys
authors.forename: Julien
authors.initials: J
authors.lastname: Doyon
authors.forename: Mélanie
authors.initials: M
authors.lastname: Pélégrini-Issac
authors.forename: Pierre
authors.initials: P
authors.lastname: Maquet
authors.forename: Habib
authors.initials: H
authors.lastname: Benali
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000502:physiology*; D016000:Cluster Analysis; D005260:Female; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000502:physiology; D012895:Sleep, REM / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology; D055815:Young Adult