An integrated analysis of the extended hippocampal system across species

Christiansen, Kathleen Yolande 2017. An integrated analysis of the extended hippocampal system across species. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The objective of this thesis was to investigate functional differences within the extended hippocampal system by 1. analysing its connectional topography and 2. looking at evidence for differential functions within its component structures. The main areas under examination were A. the subiculum and B. its diencephalic targets, along with C. the fornix, the principle white matter tract connecting these structures. Retrograde tracer experiments in rodents and primates revealed consistent topographies in the subiculum projections to these diencephalic target sites, with distinctions occurring primarily along the proximal-distal and laminar subicular axes in rodents and primarily along the anterior-posterior and laminar subicular axes in primates. Based on different input patterns to the proximal subiculum (principally from sites processing object information) and distal subiculum (principally from sites processing spatial/context information) it was predicted that this proximal-distal axis would show functional activation differences in rodents for matched object:spatial tasks. Immediate early gene imaging (using zif268 expression) did not, however, reveal clear-cut gradient differences, although there were indications of the expected bias to object memory in the proximal subiculum. Diffusion MRI was used to study the fornix by separating its precommissural and postcommissural connections in a healthy older and cognitively impaired human population. Reliable topographic differences were found for the precommissural and postcommissural fornix in each group but cognitive function proved difficult to differentiate between the tracts for the tasks used. Lastly, fornix reconstructions were also found to be separable according to their links with either the anterior or posterior hippocampus in a healthy population. These distinctions provide another way of studying the fornix in terms of relating different functional properties with different sets of hippocampal connections. It is assumed that different populations of fornical fibres should underlie different aspects of memory/ cognitive tasks involving the fornix, making their segregation informative in future studies researching this tract. detailing the nature of the connections within the extended hippocampal system, this thesis lays the groundwork for future studies investigating the relative roles of its component structures in cognitive function

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Psychology
Subjects:	B Philosophy. Psychology. Religion > BF Psychology
Date of First Compliant Deposit:	31 May 2017
Date of Acceptance:	30 May 2017
Last Modified:	10 Nov 2021 15:56
URI:	https://orca.cardiff.ac.uk/id/eprint/100977

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