Diviney, Mairead (2011) A Behavioural, Molecular and Lesion Examination of Hippocampal Contributions to Morris Water Maze Acquisition. PhD thesis, National University of Ireland Maynooth.
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Abstract
The Morris water maze (MWM) is a widely known, simple and effective task in the
examination of spatial learning and memory. Successful acquisition of the task is
thought to rely on retained representations of allocentric spatial relations, whereby
animals learn to associate the location of a hidden platform with surrounding distal cues
and subsequently use this information to navigate towards the hidden goal. As the distal
cues are critical in this process, features of the cues, such as location, are an important
factor to consider in examining how the task is solved. It has also been well
documented that the hippocampus is a critical structure in the processing of allocentric
representations. However, there has been debate surrounding the exact nature of this
involvement, with suggestions that hippocampal damage leads to deficiencies in
navigational aspects of the task rather than purely spatial processing impairments. To
assess this, we adopted novel methods of analyses which include sub-second monitoring
of each individual animal’s behaviour as they navigate during a training trial. From this
analysis we initially determine that positioning of the distal cues around the maze can
impact on intact animals’ performance. Specifically, we noted that animals with cues
positioned close to their goal are more efficient in reaching the target and use more
view-dependent strategies, over animals whose cues are in a position further away, who,
instead, are more reliant on view-independent behaviours in order to reach their goal.
Molecular examinations of both groups of animals reveal higher BDNF expression in
the dorsal hippocampus in the group whose cues are positioned further away from their
goal, which we suggest reflects the Far cue groups need to infer their position more than
the Near cue group. Following this, assessment of animal behaviour following lesions to
the dorsal hippocampus indicated that both the Near and Far lesioned groups were
significantly impaired in the MWM. Behavioural analysis highlighted lesioned animals’
deficits in accurately monitoring and adapting their motor movements in response to
task demands, suggesting that the impairments seen in the maze are due deficits in
integrating exploratory behaviours, rather than a purely spatial memory impairment.
While there were few differences in performance of the Near and Far lesioned animals,
further assessment of the intact hippocampus using immunohistochemical procedures
revealed increased c-Fos expression in the Far cue group in area CA1 of the
hippocampus. Further to this, subregional assessment using lesion and IEG
methodologies led to the distinction that the dentate gyrus, in particular, is critical in
performance in the water maze.
Together, the behavioural, molecular and lesion data assessing hippocampal
contributions to acquisition of the MWM are discussed in terms of models of
navigation. From this, we suggest that the water maze task is solved using a vectormodel
of navigation, rather than the widely reported, and accepted, cognitive mapping
theory of spatial learning. The behavioural lesion data also supports a role for the
hippocampus in this model, specifically as lesioned animals’ display clear impairments
in the accurate judgement of distance and direction to their goal when in the maze; a
critical feature of the vector-model
Item Type: | Thesis (PhD) |
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Keywords: | Hippocampal Contributions; Morris Water Maze Acquisition; |
Academic Unit: | Faculty of Science and Engineering > Psychology |
Item ID: | 3736 |
Depositing User: | IR eTheses |
Date Deposited: | 06 Jun 2012 11:14 |
URI: | https://mural.maynoothuniversity.ie/id/eprint/3736 |
Use Licence: | This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here |
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