title: Reaching across the abyss: recent advances in functional magnetic resonance imaging and their potential relevance to disorders of consciousness.
abstract: Disorders of consciousness (DOC) raise profound scientific, clinical, ethical, and philosophical issues. Growing knowledge on fundamental principles of brain organization in healthy individuals offers new opportunities for a better understanding of residual brain function in DOCs. We here discuss new perspectives derived from a recently proposed scheme of brain organization underlying consciousness in healthy individuals. In this scheme, thalamo-cortical networks can be divided into two, often antagonistic, global systems: (i) a system of externally oriented, sensory-motor networks (the "extrinsic" system); and (ii) a system of inward-oriented networks (the "intrinsic" or default system). According to this framework, four distinct mental states would be possible that could be relevant for understanding DOCs. In normal healthy volunteers and locked-in syndrome patients, a state of high functionality of both the extrinsic and intrinsic or default systems is expected--associated with full awareness of environment and self. In this case, mental imagery tasks combined with fMRI can be used to detect covert awareness in patients that are unable to communicate. According to the framework, two complementary states of system imbalance are also possible, in which one system is in a hyperfunctional state, while the other is hypoactive. Extrinsic system hyperfunction is expected to lead to a state of total sensory-motor "absorption" or "lost self." In contrast, intrinsic or default system hyperfunction is expected to lead to a state of complete detachment from the external world. A state where both extrinsic and intrinsic systems are hypofunctional is predicted to lead to markedly impaired consciousness as seen in DOCs. Finally, we review the potential use of ultra-slow fluctuations in BOLD signal as a tool for assessing the functional integrity of extrinsic and intrinsic systems during "resting state" fMRI acquisitions. In particular, we discuss the potential provided by assessment of these slow spontaneous BOLD fluctuations as a novel tool in assessing the cognitive state and chances of recovery from brain pathologies underlying DOCs.
authors.affiliation: Coma Science Group, Cyclotron Research Centre, University of Liège, Belgium. Andrea.Soddu@ulg.ac.be
authors.forename: Andrea
authors.initials: A
authors.lastname: Soddu
authors.forename: Melanie
authors.initials: M
authors.lastname: Boly
authors.forename: Yuval
authors.initials: Y
authors.lastname: Nir
authors.forename: Quentin
authors.initials: Q
authors.lastname: Noirhomme
authors.forename: Audrey
authors.initials: A
authors.lastname: Vanhaudenhuyse
authors.forename: Athena
authors.initials: A
authors.lastname: Demertzi
authors.forename: Anat
authors.initials: A
authors.lastname: Arzi
authors.forename: Smadar
authors.initials: S
authors.lastname: Ovadia
authors.forename: Mario
authors.initials: M
authors.lastname: Stanziano
authors.forename: Michele
authors.initials: M
authors.lastname: Papa
authors.forename: Steven
authors.initials: S
authors.lastname: Laureys
authors.forename: Rafael
authors.initials: R
authors.lastname: Malach
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D001921:Brain / Q000098:blood supply* / Q000503:physiopathology; D001931:Brain Mapping; D003244:Consciousness Disorders / Q000175:diagnosis* / Q000503:physiopathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007092:Imagination; D008279:Magnetic Resonance Imaging; D008959:Models, Neurological; D009415:Nerve Net / Q000098:blood supply / Q000503:physiopathology; D009434:Neural Pathways / Q000098:blood supply / Q000503:physiopathology; D009483:Neuropsychological Tests; D010100:Oxygen / Q000097:blood; D013028:Space Perception / Q000502:physiology*
chemical_list: D010100:Oxygen