title: Amnestic mild cognitive impairment: topological reorganization of the default-mode network.
abstract: OBJECTIVE
  To investigate the topologic reorganization of the default-mode network (DMN) in patients with mild cognitive impairment (MCI) and whether, relative to healthy control subjects, patients with MCI would be more likely to show disrupted functional connectivity and altered topological configuration of the DMN during the memory task compared with that observed during the resting state.
  
  
  METHODS
  This study was approved by the institutional review board of Beijing Normal University Imaging Center for Brain Research. Written informed consent was obtained from each participant. Healthy control subjects (n = 26) and patients with amnestic MCI (aMCI) (n = 25) performed an episodic memory task and also rested while undergoing functional magnetic resonance imaging. Task-induced deactivations were identified and parcellated into different regions associated with the DMN. Functional connectivity across all pairs of regions was computed to construct the DMN architecture. Graph theoretical approaches were used to characterize topological properties of this network.
  
  
  RESULTS
  Patients with aMCI showed similar deactivation in the DMN to that observed in healthy control subjects (P > .05) but showed significantly decreased anterior-to-posterior functional connectivity only during the task (P < .05). Significant increases in local efficiency (P < .05), but not in global efficiency (P > .05), were observed in aMCI only during the task. Decreased functional connectivity was predictive of increased local efficiency (r = -0.35, P = .015). Significant correlations between these network measures and cognitive performance (P < .05) indicated their potential use as early markers to assess the risk of Alzheimer disease (AD).
  
  
  CONCLUSIONS
  This study suggests the early onset functional reorganization of the DMN toward a nonoptimized regularity configuration in aMCI and expands the understanding of dynamic functional reorganization in brain networks along the continuum from normal aging to AD dementia.
authors.affiliation: State Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal University, 19 Xinjiekouwai St, Beijing 100875, P.R. China.
authors.forename: Liang
authors.initials: L
authors.lastname: Wang
authors.forename: He
authors.initials: H
authors.lastname: Li
authors.forename: Ying
authors.initials: Y
authors.lastname: Liang
authors.forename: Junying
authors.initials: J
authors.lastname: Zhang
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.forename: Ni
authors.initials: N
authors.lastname: Shu
authors.forename: Yongyan Y
authors.initials: YY
authors.lastname: Wang
authors.forename: Zhanjun
authors.initials: Z
authors.lastname: Zhang
mesh_terms: D000368:Aged; D000647:Amnesia / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D016022:Case-Control Studies; D060825:Cognitive Dysfunction / Q000503:physiopathology*; D005260:Female; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D009929:Organ Size; D011446:Prospective Studies