title: Dissociated mean and functional connectivity BOLD signals in visual cortex during eyes closed and fixation.
abstract: We investigated the effects of resting state type on blood oxygen level-dependent (BOLD) signal and functional connectivity in two paradigms: participants either alternated between fixation and eyes closed or maintained fixation or eyes closed throughout each scan. The BOLD signal and functional connectivity of lower and higher tiers of the visual cortical hierarchy were found to be differentially modulated during eyes closed versus fixation. Fixation was associated with greater mean BOLD signals in primary visual cortex and lower mean BOLD signals in extrastriate visual areas than periods of eyes closed. In addition, analysis of thalamocortical functional connectivity during scans in which participants maintained fixation showed synchronized BOLD fluctuations between those thalamic nuclei whose mean BOLD signal was systematically modulated during alternating epochs of eyes closed and fixation, primary visual cortex and the attention network, while during eyes closed negatively correlated fluctuations were seen between the same thalamic nuclei and extrastriate visual areas. Finally, in all visual areas the amplitude of spontaneous BOLD fluctuations was greater during eyes closed than during fixation. The dissociation between early and late tiers of visual cortex, which characterizes both mean and functionally connected components of the BOLD signal, may depend on the reorganization of thalamocortical networks. Since dissociated changes in local blood flow also characterize transitions between different stages of sleep and wakefulness (Braun AR, Balkin TJ, Wesenten NJ, Gwadry F, Carson RE, Varga M, Baldwin P, Belenky G, Herscovitch P. Science 279: 91-95, 1998), our results suggest that dissociated endogenous neural activity in primary and extrastriate cortex may represent a general aspect of brain function.
authors.affiliation: Department of Radiology, Washington University School of Medicine, Saint Louis, Missouri 63110, USA. mcavoy@npg.wustl.edu
authors.forename: Mark
authors.initials: M
authors.lastname: McAvoy
authors.forename: Linda
authors.initials: L
authors.lastname: Larson-Prior
authors.forename: Marek
authors.initials: M
authors.lastname: Ludwikow
authors.forename: Dongyang
authors.initials: D
authors.lastname: Zhang
authors.forename: Abraham Z
authors.initials: AZ
authors.lastname: Snyder
authors.forename: Debra L
authors.initials: DL
authors.lastname: Gusnard
authors.forename: Marcus E
authors.initials: ME
authors.lastname: Raichle
authors.forename: Giovanni
authors.initials: G
authors.lastname: d'Avossa
mesh_terms: D000328:Adult; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D010100:Oxygen / Q000097:blood*; D013787:Thalamic Nuclei / Q000502:physiology; D014793:Visual Cortex / Q000098:blood supply / Q000502:physiology*
chemical_list: D010100:Oxygen