title: The status of the precommissural and postcommissural fornix in normal ageing and mild cognitive impairment: An MRI tractography study.
abstract: The fornix connects the hippocampal formation with structures beyond the temporal lobe. Previous tractography studies have typically reconstructed the fornix as one unified bundle. However, the fornix contains two rostral divisions: the precommissural fornix and the postcommissural fornix. Each division has distinct anatomical connections and, hence, potentially distinct functions. Diffusion weighted MRI and spherical deconvolution based tractography were employed to reconstruct these separate fornix divisions and to examine their microstructural properties in both healthy ageing and Mild Cognitive Impairment (MCI). Reliable reconstructions of precommissural and postcommissural fibres were achieved in both groups, with their fibres retaining largely separate locations within the anterior body of the fornix. Ageing and MCI had comparable effects on the two segments. Ageing was associated with changes in mean, axial and radial diffusivity but not with alterations of fibre population-specific diffusion properties, estimated with the hindrance modulated orientational anisotropy (HMOA). Individual HMOA variation in postcommissural, but not precommissural, fibres correlated positively (and unrelated to age) with visual recall performance. This provides novel evidence for a role of postcommissural fibres, which connect structures of the extended hippocampal network, in episodic memory function. Separating the fornix into its two principal divisions brings new opportunities for distinguishing different hippocampal networks.
authors.affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Tower Building, 70, Park Place, Cardiff CF10 3AT, UK.
authors.forename: Kat
authors.initials: K
authors.lastname: Christiansen
authors.affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Tower Building, 70, Park Place, Cardiff CF10 3AT, UK.
authors.forename: John P
authors.initials: JP
authors.lastname: Aggleton
authors.affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Tower Building, 70, Park Place, Cardiff CF10 3AT, UK.
authors.forename: Greg D
authors.initials: GD
authors.lastname: Parker
authors.affiliation: Department of Basic and Clinical Neurosciences, Institute of Psychiatry, Psychology & Neuroscience, King's College London, UK.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Sullivan
authors.affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Tower Building, 70, Park Place, Cardiff CF10 3AT, UK.
authors.forename: Seralynne D
authors.initials: SD
authors.lastname: Vann
authors.affiliation: Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Tower Building, 70, Park Place, Cardiff CF10 3AT, UK. Electronic address: Metzler-BaddeleyC@cardiff.ac.uk.
authors.forename: Claudia
authors.initials: C
authors.lastname: Metzler-Baddeley
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000473:pathology*; D060825:Cognitive Dysfunction / Q000000981:diagnostic imaging* / Q000473:pathology; D056324:Diffusion Tensor Imaging / Q000379:methods; D005260:Female; D020712:Fornix, Brain / Q000473:pathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D061212:Memory, Episodic; D008875:Middle Aged; D009434:Neural Pathways / Q000473:pathology
keywords: Aging; Fornix; Memory; Mild cognitive impairment; Tractography