The dorsal subiculum and long-term spatial memory: A behavioural and electrophysiological study

Franceschi, Chiara 2025. The dorsal subiculum and long-term spatial memory: A behavioural and electrophysiological study. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The subiculum is a major output region of the hippocampus. While its involvement in spatial working memory is known, its contributions to reference memory have not been established. This work aimed at filling this gap. Silencing the dorsal subiculum through muscimol infusions was performed at different stages of a spatial radial-arm maze (RAM) task: acquisition, and memory processing during rest. In both instances, muscimol impaired the animals’ performance, confirming a role of the area in spatial working memory and indicating a subicular contribution to spatial reference memory. The manipulation of subicular activity was additionally tested when pre-exposure to the task was carried out. Here, no impact on performance was detected, which suggests that prior task knowledge might reduce the contribution of the subiculum in reference memory. The second part of this thesis focused on developing and implementing an electrophysiological methodology that allows characterisation of neuronal activity across consecutive days. Neuropixels probes were implanted and recorded while rats explored an open field apparatus and performed the RAM task, intermingled with sleep sessions. Stability of the recordings was assessed through waveform features using a PCA approach, which showed that it is feasible to reliably track the same cells across days. A circular clustering approach allowed to identify four subgroups of excitatory neurons, based on their theta preference. These groups differed in position along the radial axis, burstiness, mean firing, and spatial information content. Characterisation of their firing during sharp-wave ripple events was also assessed. During learning, group 1 consisted of more spatial, plastic cells. Reactivation of firing assemblies during sleep confirmed that subicular cells reactivate more on the first two days of the task, consistent with learning. Collectively, this data provides a first indication of the involvement of the dorsal subiculum in reference memory, from both a behavioural and an electrophysiological standpoint.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Psychology
Date of First Compliant Deposit:	18 December 2025
Last Modified:	18 Dec 2025 12:30
URI:	https://orca.cardiff.ac.uk/id/eprint/183323

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