title: Global field synchronization reveals rapid eye movement sleep as most synchronized brain state in the human EEG.
abstract: Sleep is characterized by a loss of consciousness, which has been attributed to a breakdown of functional connectivity between brain regions. Global field synchronization (GFS) can estimate functional connectivity of brain processes. GFS is a frequency-dependent measure of global synchronicity of multi-channel EEG data. Our aim was to explore and extend the hypothesis of disconnection during sleep by comparing GFS spectra of different vigilance states. The analysis was performed on eight healthy adult male subjects. EEG was recorded during a baseline night, a recovery night after 40 h of sustained wakefulness and at 3 h intervals during the 40 h of wakefulness. Compared to non-rapid eye movement (NREM) sleep, REM sleep showed larger GFS values in all frequencies except in the spindle and theta bands, where NREM sleep showed a peak in GFS. Sleep deprivation did not affect GFS spectra in REM and NREM sleep. Waking GFS values were lower compared with REM and NREM sleep except for the alpha band. Waking alpha GFS decreased following sleep deprivation in the eyes closed condition only. Our surprising finding of higher synchrony during REM sleep challenges the view of REM sleep as a desynchronized brain state and may provide insight into the function of REM sleep.
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland; Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland; Zurich Center for Interdisciplinary Sleep Research, University of Zurich, Zurich, Switzerland; Neuroscience Center Zurich, University of Zurich and ETH Zurich, Zurich, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Achermann
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland; University Hospital of Child and Adolescent Psychiatry and Psychotherapy, University Hospital of Psychiatry, University of Bern, Bern, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rusterholz
authors.affiliation: Institute of Pharmacology and Toxicology , University of Zurich , Zurich , Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: Dürr
authors.affiliation: Translational Research Center , University Hospital of Psychiatry , University of Bern , Bern , Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: König
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland; University Hospital of Child and Adolescent Psychiatry and Psychotherapy, University Hospital of Psychiatry, University of Bern, Bern, Switzerland; Department of Psychiatry and Human Behavior, The Alpert Medical School of Brown University, Providence, RI, USA.
authors.forename: Leila
authors.identifier: 0000-0003-4014-428X
authors.initials: L
authors.lastname: Tarokh
keywords: EEG; global field synchrony; rapid eye movement sleep; sleep