Frontal and parietal regions are associated with some of the most complex cognitive functions, and several frontoparietal resting-state networks can be observed in wakefulness. We used functional magnetic resonance imaging data acquired in polysomnographically validated wakefulness, light sleep, and slow-wave sleep to examine the hierarchical structure of a low-frequency functional brain network, and to examine whether frontoparietal connectivity would disintegrate in sleep. Whole-brain analyses with hierarchical cluster analysis on predefined atlases were performed, as well as regression of inferior parietal lobules (IPL) seeds against all voxels in the brain, and an evaluation of the integrity of voxel time-courses in subcortical regions-of-interest. We observed that frontoparietal functional connectivity disintegrated in sleep stage 1 and was absent in deeper sleep stages. Slow-wave sleep was characterized by strong hierarchical clustering of local submodules. Frontoparietal connectivity between IPL and superior medial and right frontal gyrus was lower in sleep stages than in wakefulness. Moreover, thalamus voxels showed maintained integrity in sleep stage 1, making intrathalamic desynchronization an unlikely source of reduced thalamocortical connectivity in this sleep stage. Our data suggest a transition from a globally integrated functional brain network in wakefulness to a disintegrated network consisting of local submodules in slow-wave sleep, in which frontoparietal inter-modular nodes may play a role, possibly in combination with the thalamus.
Keywords: fMRI, sleep, hierarchy, clustering, frontoparietal, network
Citation: Spoormaker VI, Gleiser PM and Czisch M (2012) Frontoparietal connectivity and hierarchical structure of the brain’s functional network during sleep. Front. Neur. 3:80. doi: 10.3389/fneur.2012.00080
Received: 08 November 2011; Paper pending published: 15 December 2011;
Accepted: 24 April 2012; Published online: 17 May 2012.
Edited by:Linda J. Larson-Prior, Washington University School of Medicine in St. Louis, USA
Reviewed by:Marcello Massimini, University of Milan, Italy
Copyright: © 2012 Spoormaker, Gleiser and Czisch. This is an open-access article distributed under the terms of the Creative Commons Attribution Non Commercial License, which permits non-commercial use, distribution, and reproduction in other forums, provided the original authors and source are credited.
*Correspondence: Victor I. Spoormaker, Neuroimaging, Max Planck Institute of Psychiatry, Kraepelinstr. 2-10, 80804 Munich, Germany. e-mail: firstname.lastname@example.org.