Overington, DW;
(2017)
Resolution of spatial ambiguity by the hippocampal place system.
Doctoral thesis , UCL (University College London).
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Abstract
External space is coded in the brain by a network of spatially modulated neurons (including place, grid, border and head direction cells), known as the ‘cognitive map’.This internal map allows flexible and efficient navigation through the external world. These neurons use both self-motion and visual landmark information to update their spatial activity and form an accurate representation of space. Sometimes, the spatial meaning of a landmark can be ambiguous, e.g. when it can be approached from different directions (for example, a tree on the border between two fields). In such cases context information, such as odour, colour or texture, can provide clues to separate one environment from another. Recent work has shown that head direction (HD) cells in the retrosplenial cortex can use these non-metric cues to resolve visually symmetrical spaces with directional landmark ambiguity. In this study, we asked whether animals can also use these nonmetric cues to guide their behaviour, in this case in order to solve spatial tasks across multi-compartment space. Here we show that, behaviourally, rodents can correctly encode relative object positions in visually ambiguous space, and can resolve the directional ambiguity of two visually symmetrical spaces based only on odour information. Electrophysiological recordings of hippocampal place and anterior thalamus HD cells confirmed that both cell types can use odour-context information to discriminate these spaces; therefore, we tested potential involvement of the HD system by temporarily inactivating the anterior thalamus with an awake muscimol infusion. In the behavioural task, HD-disrupted animals show impairment in task performance compared to sham but retain response to novelty. Overall, these results indicate that rodents can use odour-context information to resolve directional ambiguity in otherwise identical multi-compartment environments, and suggest an involvement of the HD system in this process.
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