Hayman, R.; (2006) Integration of geometric and contextual inputs to hippocampal place cells. Doctoral thesis , University of London.

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Abstract

Neurons in the rodent hippocampus fire in highly restricted portions of an environment. These place cells have receptive fields called place fields and are argued to form a representation of space. The work described in this thesis explores the different types of sensory input to these cells, how these inputs are integrated and the implications for our understanding of hippocampal processing. To this end, hippocampal pyramidal neurons were recorded from awake, behaving rats as they foraged for food in a series of different environments. By manipulating the environments to which rats were exposed the nature of the input to place cells was elucidated. The first two experiments explored the influence of geometry on place fields. A novel environment was created that facilitated an examination of how the boundaries that constituted that environment affected place field activity. It was found that the presence of boundaries was important in order to have well-defined and consistent place fields across trials. Furthermore, exposure to one environment affected the place fields recorded in a similar but different environment, suggesting that learning was occurring. The final experiment examined in greater detail the effect of learning on the place cell representation. Place cells were recorded in two neighbouring environments that were the same colour. Initially similar place cell representations were found to diverge over the course of several days and weeks such that the place cell activations in both environments became distinct. Once a distinct pattern of place cell activity was seen, the colour of the environments was changed. The learnt discrimination that was acquired in the initial environments was not transferred to the novel environment. This suggested that the information acquired by place cells was specific to a given environment. These results are incorporated into, and extend, an existing model of place field formation.

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