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Title: Hippocampal neuron firing in geometrically different environments : evidence for long term, incidental and incremental learning
Author: Lever, Colin
ISNI:       0000 0001 3608 5972
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2001
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When rats move around environments, hippocampal neurons fire in restricted portions of these environments. These neurons are thus called place cells, and are thought to provide the rat with a map-like representation of space, which can be used to guide behaviours such as navigation, and environmental discrimination. Previous work has indicated that place cells can show different firing patterns in different environments (O'Keefe and Conway, 1978; Kubie and Ranck, 1983). This phenomenon is often referred to as "remapping" (Muller, 1996). Previous studies had shown different patterns of firing in differently-shaped walled environments (Muller and Kubie, 1987). In particular, place cell remapping was reported between square-walled, and circular-walled boxes (Quirk et al, 1992; Sharp, 1997). The present study re-examined the remapping phenomenon in square-walled and circular-walled boxes under controlled conditions which did not alter the rats' directional sense. All the experiments conducted for this study showed that remapping did not take place on initial trials in the boxes; the firing patterns in the two boxes were similar. This basic result stands in contrast to that of Quirk et al, 1992 and Sharp, 1997. Further experiments showed that although place cell patterns were initially very similar across the two boxes, the patterns diverged with experience. In the time-series experiment designed to examine this issue carefully, the results showed a correlation between the amount of experience and the amount of remapping. The transition from similar to remapped firing patterns was gradual. This is interpreted as evidence for incidental and incremental hippocampal discriminatory learning; the hippocampus learns to represent two boxes as different that it initially considers similar. Further study showed that this acquired pattern-alteration was stable after a delay period of a month, during which the animals were not exposed to the testing environment. When re-tested the patterns showed similar levels of remapping to that obtained at the end of the time-series experiment. This is interpreted as important evidence for long-term storage of learned patterns. Other tests are described which were intended to probe the nature of the initial similarity, and subsequent divergence, of the place cell firing patterns. Also described is an attempt to show transfer of knowledge from one environment to another. It is argued that the present thesis makes a contribution to our understanding of learning and memory processes in the hippocampus.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Place cells