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Title: Memories along the longitudinal axis of a rodent hippocampus : acquisition and consolidation of variants of a spatial task
Author: de Hoz, Livia
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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The mammalian hippocampus is a structure of the brain believed to be essential in learning and memory processes. A current controversy concerns whether it is involved in one unique memory process or is responsible for several related but dissociable functions. And irrespective of the function(s) there is controversy concerning its role in processes of memory consolidation. This thesis, divided in two parts, addresses these two issues. Part I: Published studies have suggested that hippocampal involvement in spatial memory acquisition is restricted to the septal (or dorsal) part of the structure, a result that supports the idea that the septal and temporal (ventral) parts of the structure have different functions. In the first part of this thesis I explore further the possibility of functional dissociations along the septotemporal axis of the hippocampus, including the importance of commissural projections. Partial lesions are made to the septal or temporal parts of the rat hippocampus, on one side or both. The behavioural essay involves acquisition of a spatial task (variants of reference memory in the watermaze). Although the original septal versus temporal dissociation is replicated, variations of the task protocol (number of days and trials per day of training) reveal that the temporal hippocampus can also support spatial memory. Learning can be attained with as little as 30% of the hippocampus spared. The results support the idea that the hippocampus is responsible for a unique process to which the projections to the septal and temporal parts, as well as the commissural associations, contribute differently. This contribution could be dependent on the training protocol. Part II: It is well established that damage to the hippocampus, across different species, can result in graded retrograde amnesia. This has be taken by some to imply a role in the consolidation, as well as the acquisition, of memories. The second part of the thesis describes a series of collaborative experiments in which the involvement of the hippocampus in acquisition, consolidation and retrieval of spatial memories is explored. Using an AMPA receptor antagonist the septal part of the hippocampus is temporarily inactivated during acquisition, retrieval or during the memory retention interval of a watermaze reference memory task. The results reveal the hippocampus is involved in all three memory processes when animals are tested 16 days after the end of acquisition. However it is believed that once a memory has been consolidated, its retrieval can occur independently of the hippocampus. Animal experiments suggesting this involved lesions of the septal hippocampus only. In work reported in this thesis, lesions to the septal or the whole hippocampus are made at different times (1 day or 6 weeks) after acquisition. Using a novel memory testing protocol, the temporal 30% of the hippocampus was found to be sufficient in the retrieval of this memory in a time-independent manner. Animals given lesions to the whole of the structure could not be reminded of what they had leamt earlier at either interval. The results suggest that the whole hippocampus is necessary for the consolidation of memories acquired with an intact hippocampus and that at least part of the hippocampus is necessary for retrieval of memories. The results obtained in part two of the thesis could be dependent on the training and testing protocol as well as on the navigational aspects of the task.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available