title: Vascular and degenerative processes differentially affect regional interhemispheric connections in normal aging, mild cognitive impairment, and Alzheimer disease.
abstract: OBJECTIVE
  Despite the critical importance of the corpus callosum (CC) to the connection between brain hemispheres, little is known about the independent contribution of degenerative and vascular processes to regional changes in the microstructural integrity of the CC. Here, we examine these changes in subjects with mild cognitive impairment, with Alzheimer disease, and in cognitively normal elderly adults.
  
  
  METHODS
  We used 3-dimensional brain MRI with diffusion tensor imaging in 47 Alzheimer disease, 77 mild cognitive impairment, and 107 cognitively normal subjects, and we calculated mean fractional anisotropy (FA) values for 4 CC regions corresponding to 4 homologous regions of cortical gray matter (GM). To assess vascular and degenerative processes, we also measured cortical GM and white matter hyperintensity (WMH) volume in corresponding regions and evaluated their vascular risk.
  
  
  RESULTS
  We found that GM volumes in anterior and posterior regions were significantly related to FA values in the corresponding regions of the CC for all 3 diagnostic groups. Independent of GM volume, frontal WMH volume was also associated with FA values in the corresponding CC regions, but posterior WMH volume was not. Vascular risk was associated with FA of most CC regions, whereas diagnosis of cognitive state was associated only with FA of the anterior and posterior CC regions.
  
  
  CONCLUSIONS
  We found differential region-specific associations between degenerative and vascular processes and the structural integrity of the CC across the spectrum of cognitive ability. Based on these results, we propose a model to explain regional disruption in the interhemispheric connection.
authors.affiliation: Imaging of Dementia and Aging (IDeA) Laboratory, Department of Neurology and Center for Neuroscience, University of California at Davis, Davis, Calif 95616, USA.
authors.forename: Dong Young
authors.initials: DY
authors.lastname: Lee
authors.forename: Evan
authors.initials: E
authors.lastname: Fletcher
authors.forename: Oliver
authors.initials: O
authors.lastname: Martinez
authors.forename: Natalia
authors.initials: N
authors.lastname: Zozulya
authors.forename: Jane
authors.initials: J
authors.lastname: Kim
authors.forename: Jeannie
authors.initials: J
authors.lastname: Tran
authors.forename: Michael
authors.initials: M
authors.lastname: Buonocore
authors.forename: Owen
authors.initials: O
authors.lastname: Carmichael
authors.forename: Charles
authors.initials: C
authors.lastname: DeCarli
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology* / Q000502:physiology; D000544:Alzheimer Disease / Q000473:pathology* / Q000503:physiopathology; D000704:Analysis of Variance; D016880:Anisotropy; D002561:Cerebrovascular Disorders / Q000473:pathology* / Q000503:physiopathology; D003072:Cognition Disorders / Q000473:pathology* / Q000503:physiopathology; D003337:Corpus Callosum / Q000473:pathology* / Q000503:physiopathology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009410:Nerve Degeneration / Q000473:pathology* / Q000503:physiopathology; D009413:Nerve Fibers, Myelinated / Q000473:pathology; D018570:Risk Assessment