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Involvement of hippocampal subfields and anterior-posterior subregions in encoding and retrieval of item, spatial, and associative memories: Longitudinal versus transverse axis

Hrybouski, Stanislau; MacGillivray, Melanie; Huang, Yushan; Madan, Christopher R.; Carter, Rawle; Seres, Peter; Malykhin, Nikolai V.

Authors

Stanislau Hrybouski

Melanie MacGillivray

Yushan Huang

Rawle Carter

Peter Seres

Nikolai V. Malykhin



Abstract

The functional role of the hippocampal formation in episodic memory has been studied using functional magnetic resonance imaging (fMRI) for many years. The hippocampus can be segmented into three major anteroposterior sections, called head, body and tail, and into the Cornu Ammonis (CA), dentate gyrus (DG), and subiculum (Sub) subfields based on its transverse axis. However, the exact role of these subregions and subfields in memory processes is less understood. In the present study we combined ultra-high resolution structural Magnetic Resonance Imaging (MRI) at 4.7 T with an event-related high-resolution fMRI paradigm based on the ‘Designs’ subtest of the Wechsler Memory Scale to investigate how the hippocampal subfields and longitudinal subregions are involved in encoding and retrieval of item, spatial, and associative memories. Our results showed that during memory encoding, regardless of the type of memory being learned, all subregions and all subfields were active. During the retrieval phase, on the other hand, we observed an anterior to posterior gradient in hippocampal activity for all subfields and all types of memory. Our findings also confirmed presence of an anterior to posterior gradient in hippocampal activity during spatial learning. Comparing subfield activities to each other revealed that the DG was more active than the CA1-3 and Sub during both encoding and retrieval. Finally, our results showed that for every subfield, encoding vs. retrieval activity differences were larger in the hippocampal head than in the hippocampal body and tail. Furthermore, these encoding vs. retrieval activity differences were similar in all subfields, highlighting the importance of studying both the longitudinal and transverse axis specialization simultaneously. Current findings further elucidate the structure–function relationship between the human hippocampus and episodic memory.

Journal Article Type Article
Publication Date May 1, 2019
Journal NeuroImage
Print ISSN 1053-8119
Electronic ISSN 1095-9572
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 191
Pages 568-586
APA6 Citation Hrybouski, S., MacGillivray, M., Huang, Y., Madan, C. R., Carter, R., Seres, P., & Malykhin, N. V. (2019). Involvement of hippocampal subfields and anterior-posterior subregions in encoding and retrieval of item, spatial, and associative memories: Longitudinal versus transverse axis. NeuroImage, 191, 568-586. https://doi.org/10.1016/j.neuroimage.2019.01.061
DOI https://doi.org/10.1016/j.neuroimage.2019.01.061
Keywords High-resolution fMRI; Hippocampal subregions; Hippocampal subfields; Memory encoding; Memory retrieval
Publisher URL https://www.sciencedirect.com/science/article/pii/S1053811919300618

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