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Place field plasticity and directionality in a spatial memory task

Martin, Patrick Dov; (1996) Place field plasticity and directionality in a spatial memory task. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

In order to determine whether hippocampal units display firing which is modulated by the demands of a spatial memory task rats were trained in an enclosed "cue controlled environment" (CCE) consisting of four platforms and six spatial cues that identified one of the four platforms as the goal. Rats learned to select the goal platform at the end of the trial even when the cues defined the goal platform were removed mid-way through the trial. In a previous study (O'Keefe and Speakman, 1987a) place fields were shown to be controlled by the spatial cues such that rotation of the cues caused concomitant rotation of the fields. They also found that the place fields continued to fire after removal of the cues. Thus although the place fields were controlled by the six spatial cues they were not dependent on them. In the present study we confirm the above findings and report two new responses. Some hippocampal place units were observed to increase or initiate place specific firing after cue removal. Others decreased or ceased place specific firing after cue removal. Thus place field location and place field intensity appears to be governed by the presence or absence of the six spatial cues. Previous work has shown that place fields show directionality when a rat traverses an open field in a restricted and stereotypical manner (McNaughton et al, 1983a; Marcus et al, 1995). Rats trained on the CCE spatial memory task were shaped to run in a raster pattern to insure uniform platform coverage. The place fields recorded in this situation were found to display directionality oriented with respect to the six spatial cues. Moreover the directionality of place fields was found to persist after the six spatial cues were removed. Thus place field directionality appears to be initially configured by the six spatial cues but is subsequently independent of them. O'Keefe and Speakman (1987a) examined error trials in which the rat failed to choose the goal platform. They found that the place field firing displayed by the hippocampus before the rat chose a platform could be used to predict the rat's choice. In the present study the hippocampal error trial firing could be use to predict the choice the rat made in some instances as per O'Keefe and Speakman (1987a). However in the majority of instances the hippocampal error trial firing was completely unrelated to that seen in previously recorded correct trials and in one instance the hippocampal error trial firing predicted that the rat would choose correctly.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Place field plasticity and directionality in a spatial memory task
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
URI: https://discovery.ucl.ac.uk/id/eprint/10101110
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