title: Scale-free functional connectivity of the brain is maintained in anesthetized healthy participants but not in patients with unresponsive wakefulness syndrome.
abstract: Loss of consciousness in anesthetized healthy participants and in patients with unresponsive wakefulness syndrome (UWS) is associated with substantial alterations of functional connectivity across large-scale brain networks. Yet, a prominent distinction between the two cases is that after anesthesia, brain connectivity and consciousness are spontaneously restored, whereas in patients with UWS this restoration fails to occur, but why? A possible explanation is that the self-organizing capability of the brain is compromised in patients with UWS but not in healthy participants undergoing anesthesia. According to the theory of self-organized criticality, many natural complex systems, including the brain, evolve spontaneously to a critical state wherein system behaviors display spatial and/or temporal scale-invariant characteristics. Here we tested the hypothesis that the scale-free property of brain network organization is in fact fundamentally different between anesthetized healthy participants and UWS patients. We introduced a novel, computationally efficient approach to determine anatomical-functional parcellation of the whole-brain network at increasingly finer spatial scales. We found that in healthy participants, scale-free distributions of node size and node degree were present across wakefulness, propofol sedation, and recovery, despite significant propofol-induced functional connectivity changes. In patients with UWS, the scale-free distribution of node degree was absent, reflecting a fundamental difference between the two groups in adaptive reconfiguration of functional interaction between network components. The maintenance of scale-invariance across propofol sedation in healthy participants suggests the presence of persistent, on-going self-organizing processes to a critical state--a capacity that is compromised in patients with UWS.
authors.affiliation: Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America.
authors.forename: B Douglas
authors.initials: BD
authors.lastname: Ward
authors.affiliation: Department of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Binder
authors.affiliation: Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America.
authors.forename: Shi-Jiang
authors.initials: SJ
authors.lastname: Li
authors.affiliation: Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America.
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Hudetz
mesh_terms: D000328:Adult; D000465:Algorithms; D000758:Anesthesia; D001921:Brain / Q000503:physiopathology*; D003243:Consciousness / Q000502:physiology; D054810:Deep Sedation; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology*; D014851:Wakefulness / Q000502:physiology*; D055815:Young Adult