Abstract
There is a paucity of information about how human hippocampal subfields are functionally connected to each other and to neighbouring extra-hippocampal cortices. In particular, little is known about whether patterns of functional connectivity (FC) differ down the anterior-posterior axis of each subfield. Here, using high resolution structural MRI we delineated the hippocampal subfields in healthy young adults. This included the CA fields, separating DG/CA4 from CA3, separating the pre/parasubiculum from the subiculum, and also segmenting the uncus. We then used high resolution resting state functional MRI to interrogate FC. We first analysed the FC of each hippocampal subfield in its entirety, in terms of FC with other subfields and with the neighbouring regions, namely entorhinal, perirhinal, posterior parahippocampal and retrosplenial cortices. Next, we analysed FC for different portions of each hippocampal subfield along its anterior-posterior axis, in terms of FC between different parts of a subfield, FC with other subfield portions, and FC of each subfield portion with the neighbouring cortical regions of interest. We found that intrinsic functional connectivity between the subfields aligned generally with the tri-synaptic circuit but also extended beyond it. Our findings also revealed that patterns of functional connectivity between the subfields and neighbouring cortical areas differed markedly along the anterior-posterior axis of each hippocampal subfield. Overall, these results contribute to ongoing efforts to characterise human hippocampal subfield connectivity, with implications for understanding hippocampal function.
Highlights
High resolution resting state functional MRI scans were collected
We investigated functional connectivity (FC) of human hippocampal subfields
We specifically examined FC along the anterior-posterior axis of subfields
FC between subfields extended beyond the canonical tri-synaptic circuit
Different portions of subfields showed different patterns of FC with neocortex
- Abbreviations
- A
- Anterior (of the hippocampus)
- AB
- Anterior body (of the hippocampus)
- CA 1-4
- Cornu ammonis 1-4
- DG
- Dentate gyrus
- DMN
- Default mode network
- ENT
- Entorhinal cortex
- FC
- Functional connectivity
- PB
- Posterior body (of the hippocampus)
- PHC
- Posterior parahippocampal cortex
- PRC
- Perirhinal cortex
- RSC
- Retrosplenial cortex
- rsfMRI
- Resting state functional magnetic resonance imaging
- T
- Tail (of the hippocampus)