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Neural encoding of the vertical plane in freely-moving rats

Casali, Giulio; (2017) Neural encoding of the vertical plane in freely-moving rats. Doctoral thesis , UCL (University College London);. Green open access

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Abstract

Grid cells produce a periodic hexagonal array of firing fields when the rat navigates on a horizontal 2D surface, and such regularity supports the hypothesis that they encode distances covered by the animal. This computation is thought to form the neural basis for path integration, and the medial entorhinal cortex (MEC), where grid cells are mostly found, is now believed to play a major role for the establishment of a cognitive map in the brain. However, while grid cells on the horizontal plane are invariant across different environments (they provide fixed spatial metrics), it is currently not known whether those distances vary in 3D space. Previous findings suggested that grid cells may be substantially incapable to perform path integration in the vertical plane and this thesis aimed to test a number of hypothesis to explain such an impairment. These results show that grid cells are not affected by experience with 3D locomotion; they are modulated by the orientation of the locomotion plane and on a climbing wall they display heavily distorted firing patterns with expanded but fewer fields. Based on these findings, the hypothesis that the inconsistency between horizontal and vertical maps may be due to the miscomputation of instantaneous speed was suggested. Preliminary results support the view that the speed signal carried by speed cells (single-unit level) and LFP theta oscillation (large ensembles) was substantially reduced suggesting an underestimation of speed during climbing. Put together these results support the hypothesis that the speed signal plays a crucial role for the generation of a regular grid. In the vertical dimension the speed signal is reduced and such impairment drives grid cells to expand and become more irregular. Overall these results demonstrate that the neural representation of space is therefore not symmetrical across dimensions but is instead anisotropic.

Type: Thesis (Doctoral)
Title: Neural encoding of the vertical plane in freely-moving rats
Event: UCL (University College London);
Open access status: An open access version is available from UCL Discovery
Language: English
Keywords: Grid cells, Place cells, Hippocampus, Medial entorhinal cortex, Spatial cognition
UCL classification: UCL > School of Life and Medical Sciences
UCL > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > School of Life and Medical Sciences > Faculty of Life Sciences > Biosciences (Division of) > Cell and Developmental Biology
URI: http://discovery.ucl.ac.uk/id/eprint/1574517
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