title: Structural covariance of superficial white matter in mild Alzheimer's disease compared to normal aging.
abstract: BACKGROUND
  Interindividual variations in regional structural properties covary across the brain, thus forming networks that change as a result of aging and accompanying neurological conditions. The alterations of superficial white matter (SWM) in Alzheimer's disease (AD) are of special interest, since they follow the AD-specific pattern characterized by the strongest neurodegeneration of the medial temporal lobe and association cortices.
  
  
  METHODS
  Here, we present an SWM network analysis in comparison with SWM topography based on the myelin content quantified with magnetization transfer ratio (MTR) for 39 areas in each hemisphere in 15 AD patients and 15 controls. The networks are represented by graphs, in which nodes correspond to the areas, and edges denote statistical associations between them.
  
  
  RESULTS
  In both groups, the networks were characterized by asymmetrically distributed edges (predominantly in the left hemisphere). The AD-related differences were also leftward. The edges lost due to AD tended to connect nodes in the temporal lobe to other lobes or nodes within or between the latter lobes. The newly gained edges were mostly confined to the temporal and paralimbic regions, which manifest demyelination of SWM already in mild AD.
  
  
  CONCLUSIONS
  This pattern suggests that the AD pathological process coordinates SWM demyelination in the temporal and paralimbic regions, but not elsewhere. A comparison of the MTR maps with MTR-based networks shows that although, in general, the changes in network architecture in AD recapitulate the topography of (de)myelination, some aspects of structural covariance (including the interhemispheric asymmetry of networks) have no immediate reflection in the myelination pattern.
authors.affiliation: LREN, Department of Clinical Neuroscience, Centre Hospitalier Universitaire Vaudois (CHUV), University of Lausanne Lausanne, Switzerland.
authors.forename: Cristian
authors.initials: C
authors.lastname: Carmeli
authors.affiliation: Department of Radiology, Centre Hospitalier Universitaire Vaudois (CHUV), University of Lausanne Lausanne, Switzerland ; CIBM (Centre d'Imagérie Biomédicale), CHUV Unit Lausanne, Switzerland.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Fornari
authors.affiliation: Department of Computer Engineering, Sharif University of Technology Tehran, Iran ; School of Electrical and Computer Engineering, RMIT University Melbourne, Australia.
authors.forename: Mahdi
authors.initials: M
authors.lastname: Jalili
authors.affiliation: Department of Radiology, Centre Hospitalier Universitaire Vaudois (CHUV), University of Lausanne Lausanne, Switzerland ; CIBM (Centre d'Imagérie Biomédicale), CHUV Unit Lausanne, Switzerland.
authors.forename: Reto
authors.initials: R
authors.lastname: Meuli
authors.affiliation: LREN, Department of Clinical Neuroscience, Centre Hospitalier Universitaire Vaudois (CHUV), University of Lausanne Lausanne, Switzerland ; Department of Radiology, Centre Hospitalier Universitaire Vaudois (CHUV), University of Lausanne Lausanne, Switzerland.
authors.forename: Maria G
authors.initials: MG
authors.lastname: Knyazeva
mesh_terms: D000368:Aged; D000375:Aging / Q000473:pathology*; D000465:Algorithms; D000544:Alzheimer Disease / Q000473:pathology*; D016022:Case-Control Studies; D003711:Demyelinating Diseases / Q000473:pathology*; D005260:Female; D006801:Humans; D065726:Limbic Lobe / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009186:Myelin Sheath / Q000378:metabolism; D012720:Severity of Illness Index; D013702:Temporal Lobe / Q000473:pathology*; D066127:White Matter / Q000473:pathology*
keywords: Connectivity; U-fibers; graph theory; interhemispheric asymmetry; magnetization transfer imaging