title: The effects of hippocampal lesions on MRI measures of structural and functional connectivity.
abstract: Focal lesions can affect connectivity between distal brain regions (connectional diaschisis) and impact the graph-theoretic properties of major brain networks (connectomic diaschisis). Given its unique anatomy and diverse range of functions, the hippocampus has been claimed to be a critical "hub" in brain networks. We investigated the effects of hippocampal lesions on structural and functional connectivity in six patients with amnesia, using a range of magnetic resonance imaging (MRI) analyses. Neuropsychological assessment revealed marked episodic memory impairment and generally intact performance across other cognitive domains. The hippocampus was the only brain structure exhibiting reduced grey-matter volume that was consistent across patients, and the fornix was the only major white-matter tract to show altered structural connectivity according to both diffusion metrics. Nonetheless, functional MRI revealed both increases and decreases in functional connectivity. Analysis at the level of regions within the default-mode network revealed reduced functional connectivity, including between nonhippocampal regions (connectional diaschisis). Analysis at the level of functional networks revealed reduced connectivity between thalamic and precuneus networks, but increased connectivity between the default-mode network and frontal executive network. The overall functional connectome showed evidence of increased functional segregation in patients (connectomic diaschisis). Together, these results point to dynamic reorganization following hippocampal lesions, with both decreased and increased functional connectivity involving limbic-diencephalic structures and larger-scale networks. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc.
authors.affiliation: MRC Cognition & Brain Sciences Unit, Cambridge, England. rik.henson@mrc-cbu.cam.ac.uk.
authors.forename: Richard N
authors.initials: RN
authors.lastname: Henson
authors.affiliation: MRC Cognition & Brain Sciences Unit, Cambridge, England.
authors.forename: Andrea
authors.initials: A
authors.lastname: Greve
authors.affiliation: MRC Cognition & Brain Sciences Unit, Cambridge, England.
authors.forename: Elisa
authors.initials: E
authors.lastname: Cooper
authors.affiliation: Neuropsychology Department, Addenbrooke's Hospital, Cambridge University Hospitals NHS Foundation Trust, Cambridge, England.
authors.forename: Mariella
authors.initials: M
authors.lastname: Gregori
authors.affiliation: Department of Psychology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Jon S
authors.initials: JS
authors.lastname: Simons
authors.affiliation: MRC Cognition & Brain Sciences Unit, Cambridge, England.
authors.forename: Linda
authors.initials: L
authors.lastname: Geerligs
authors.affiliation: MRC Cognition & Brain Sciences Unit, Cambridge, England.
authors.forename: Sharon
authors.initials: S
authors.lastname: Erzinçlioğlu
authors.affiliation: Research Department of Clinical, Educational and Health Psychology, University College London, London, United Kingdom.
authors.forename: Narinder
authors.initials: N
authors.lastname: Kapur
authors.affiliation: Neuropsychology Department, Addenbrooke's Hospital, Cambridge University Hospitals NHS Foundation Trust, Cambridge, England.
authors.forename: Georgina
authors.initials: G
authors.lastname: Browne
mesh_terms: D000328:Adult; D000368:Aged; D000647:Amnesia / Q000000981:diagnostic imaging / Q000209:etiology*; D001930:Brain Injuries / Q000150:complications / Q000000981:diagnostic imaging*; D001931:Brain Mapping; D005260:Female; D066128:Gray Matter / Q000000981:diagnostic imaging; D006624:Hippocampus / Q000000981:diagnostic imaging* / Q000293:injuries / Q000503:physiopathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000000981:diagnostic imaging; D009483:Neuropsychological Tests; D010100:Oxygen / Q000097:blood; D066127:White Matter / Q000000981:diagnostic imaging
chemical_list: D010100:Oxygen
keywords: DTI; VBM; amnesia; diaschisis; functional connectivity; hippocampus; structural connectivity