Recovery of spatial performance in the Morris Water Maze following bilateral transection of the fimbria/fornix in rats

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dc.contributor.authorHannesson, Darren Keithen_US
dc.date.accessioned2024-08-14T16:42:04Z
dc.date.available2024-08-14T16:42:04Z
dc.date.copyright1995en_US
dc.date.issued1995
dc.degree.departmentDepartment of Psychology
dc.degree.levelMaster of Arts M.A.en
dc.description.abstractA considerable body of research implicates the hippocampus in spatial cognition. In particular, lesion studies have shown that damage to the various components of the hippocampal system (including the hippocampus proper, dentate gyrus, entorhinal cortex, subiculum, and fimbria/fornix [FF]) produces deficits on a wide variety of spatial tasks. However, an increasing number of studies have also shown that, in some instances, spatial performance recovers after subtotal lesions to the hippocampal system. This suggests that considerable capacity for spatial cognition may recover or persist following such lesions. The present study sought to determine whether spatial performance in the Morris water maze (MWM) recovers after bilateral transection of the FF in rats, whether such recovery results from restored or residual spatial cognitive capacity, and what contribution, if any, pre-operative training makes to such recovery. Rats were administered extensive training to a constant submerged platform location with probe tests utilized frequently to assess performance strategies. Following the attainment of asymptotic performance levels, rats were tested for acquisition of a subsequent platform location. FF lesions were found to produce a severe impairment both in pre-operatively trained rats (a retention or retrieval deficit) and in naive rats (an acquisition deficit) as shown by the use of indirect routes to the platform on submerged platform trials and an absence of localized searching in the platform's area on probe trials. However, with extensive training, performance recovered in both groups, such that they eventually used direct escape routes to the submerged platform and showed highly localized searching in its area on probe trials. When tested for acquisition of a second platform location, a substantial deficit reappeared which was again followed by recovery with extensive training. Pre-operative training was found to attenuate the initial post-operative deficit and speed recovery but did not affect symptotic performance levels nor acquisition of a subsequent platform location. These data show that, though spatial cognition is impaired, spatial performance in the MWM eventually recovers after FF lesions and pre-operative training, though perhaps initially beneficial, is not essential for this recovery. The deficit shown in acquisition of the second platform location argues against the occurrence of recovery of spatial cognition and suggests that the basis of recovered performance is residual spatial cognitive capacity which has the following limitations: i) rate of acquisition of spatial information is reduced, ii) utilization of spatial information stored pre-operatively is restricted, and ii) translation of spatial information into navigational behaviour is less efficient. The neural bases of this residual system are speculated to include spared intra-hippocampal storage mechanisms and/or mechanisms involved in extra-hippocampal long-term memory consolidation while the neural bases of the FF's contribution to spatial information storage in the intact brain are speculated to involve theta synchronization of hippocampal activity and the induction and expression of hippocampal long-term potentiation.
dc.format.extent88 pages
dc.identifier.urihttps://hdl.handle.net/1828/18034
dc.rightsAvailable to the World Wide Weben_US
dc.titleRecovery of spatial performance in the Morris Water Maze following bilateral transection of the fimbria/fornix in ratsen_US
dc.typeThesisen_US

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