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Parcellation of the Hippocampus Using Resting Functional Connectivity in Temporal Lobe Epilepsy

Barnett, Alexander J. and Man, Vincent and McAndrews, Mary Pat (2019) Parcellation of the Hippocampus Using Resting Functional Connectivity in Temporal Lobe Epilepsy. Frontiers in Neurology, 10 . Art. No. 920. ISSN 1664-2295.

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We have previously shown that the connectivity of the hippocampus to other regions of the default mode network (DMN) is a strong indicator of memory ability in people with temporal lobe epilepsy (TLE). Recent work in the cognitive neuroscience literature has suggested that the anterior and posterior aspects of the hippocampus have distinct connections to the rest of the DMN and may support different memory operations. Further, structural analysis of epileptogenic hippocampi has found greater atrophy, characterized by mesial temporal sclerosis, in the anterior region of the hippocampus. Here, we used resting state FMRI data to parcellate the hippocampus according to its functional connectivity to the rest of the brain in people with left lateralized TLE (LTLE) and right lateralized TLE (RTLE), and in a group of neurologically healthy controls. We found similar anterior and posterior compartments in all groups. However, there was weaker connectivity of the epileptogenic hippocampus to multiple regions of the DMN. Both TLE groups showed reduced connectivity of the posterior hippocampus to key hubs of the DMN, the posterior cingulate cortex (PCC) and the medial pre-frontal cortex (mPFC). In the LTLE group, the anterior hippocampus also showed reduced connectivity to the DMN, and this effect was influenced by the presence of mesial temporal sclerosis. When we explored brain-behavior relationships, we found that reduced connectivity of the left anterior hippocampus to the DMN hubs related to poorer verbal memory ability in people with LTLE, and reduced connectivity of the right posterior hippocampus to the PCC related to poorer visual memory ability in those with RTLE. These findings may inform models regarding functional distinctions of the hippocampal anteroposterior axis.

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Additional Information:© 2019 Barnett, Man and McAndrews. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Received: 09 February 2019; Accepted: 07 August 2019; Published: 22 August 2019. Ethics Statement: Informed consent was obtained from all subjects in this study, which was approved by the UHN Research Ethics Board. Author Contributions: AB: study design, data collection, and analysis and manuscript drafting. VM: k-means clustering analysis and manuscript editing. MM: study design, supervision of data collection, and manuscript drafting. This research was supported by grants from the Canadian Institute of Health Research (CIHR Project Grant 148762 to MM) and by EpLink—The Epilepsy Research Program of the Ontario Brain Institute (OBI). The OBI is an independent non-profit corporation, funded partially by the Ontario government. The opinions, results and conclusions are those of the authors, and no endorsement by EpLink or the OBI is intended or should be inferred. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The authors would like to thank all the participants for their time and contribution. We are also grateful to Melanie Cohn, David Gold, and Irene Giannoyis for their help in characterizing clinical demographics. Supplementary Material: The Supplementary Material for this article can be found online at:
Funding AgencyGrant Number
Canadian Institutes of Health Research (CIHR)148762
Ontario Brain InstituteUNSPECIFIED
Subject Keywords:hippocampus, epilepsy, resting state, memory, long axis, default mode network
Record Number:CaltechAUTHORS:20190905-100036909
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Official Citation:Barnett AJ, Man V and McAndrews MP (2019) Parcellation of the Hippocampus Using Resting Functional Connectivity in Temporal Lobe Epilepsy. Front. Neurol. 10:920. doi: 10.3389/fneur.2019.00920
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98426
Deposited By: Tony Diaz
Deposited On:05 Sep 2019 19:35
Last Modified:03 Oct 2019 21:41

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