title: Temporal association tracts and the breakdown of episodic memory in mild cognitive impairment.
abstract: OBJECTIVE
  To examine the pattern of association between microstructure of temporal lobe connections and the breakdown of episodic memory that is a core feature of mild cognitive impairment (MCI).
  
  
  METHODS
  Twenty-five individuals with MCI and 20 matched controls underwent diffusion MRI and cognitive assessment. Three temporal pathways were reconstructed by tractography: fornix, parahippocampal cingulum (PHC), and uncinate fasciculus. Tissue volume fraction-a tract-specific measure of atrophy-and microstructural measures were derived for each tract. To test specificity of associations, a comparison tract (corticospinal tract) and control cognitive domains were also examined.
  
  
  RESULTS
  In MCI, tissue volume fraction was reduced in the fornix. Axial and radial diffusivity were increased in uncinate and PHC implying more subtle microstructural change. In controls, tissue volume fraction in the fornix was the predominant correlate of free recall. In contrast, in MCI, the strongest relationship was with left PHC. Microstructure of uncinate and PHC also correlated with recognition memory, and recognition confidence, in MCI.
  
  
  CONCLUSIONS
  Episodic memory in MCI is related to the structure of multiple temporal association pathways. These associations are not confined to the fornix, as they are in healthy young and older adults. In MCI, because of a compromised fornix, alternative pathways may contribute disproportionally to episodic memory performance.
authors.affiliation: Cardiff University Brain Research Imaging Centre, School of Psychology, and the Neuroscience and Mental Health Research Institute, Cardiff University, Cardiff, UK.
authors.forename: Claudia
authors.initials: C
authors.lastname: Metzler-Baddeley
authors.forename: Sarah
authors.initials: S
authors.lastname: Hunt
authors.forename: Derek K
authors.initials: DK
authors.lastname: Jones
authors.forename: Alexander
authors.initials: A
authors.lastname: Leemans
authors.forename: John P
authors.initials: JP
authors.lastname: Aggleton
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Sullivan
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D060825:Cognitive Dysfunction / Q000503:physiopathology* / Q000523:psychology; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D008297:Male; D061212:Memory, Episodic; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology*; D009434:Neural Pathways / Q000503:physiopathology; D009483:Neuropsychological Tests; D013702:Temporal Lobe / Q000503:physiopathology*