Rathore, Shailendra; (2017) The sensory and behavioural determinants of neuronal activity in the Subiculum. Doctoral thesis (PhD), UCL (University College London).

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Abstract

The hippocampal formation is focal in generating representations of space and supporting episodic memory. The recent discovery of boundary responsive cells in the Subiculum and Medial Entorhinal Cortex demonstrate the first explicit coding of environmental boundaries, with these cells responding to boundaries of the environment, inserted boundaries and traversable drops. The firing of these cells has been shown to be key to anchoring place and grid cells and may be a basis for place cell formation. How these neurons integrate sensory information about barriers is unknown and no model-driven approach has been developed to detect such responses. Furthermore rearing behaviour induced in novelty and boundary interaction has received little attention. We firstly show that most of the neurons in the Subiculum respond to an insertion of barrier, with many parametrically increasing their firing rate with barrier height. We confirm the existence of path integrative information in the Subiculum and show improvements in position decoding from Subicular ensembles in the presence of barrier. Secondly we show a robust method for classifying rearing and utilize it to describe the behaviour in two novel environments. We find a general reduction in firing rate of Subicular cells during rearing, the degree of this reduction reflecting nearest wall distance in only the walled environment and the spatiality of the cells. Finally we demonstrate accurate classification of different boundary vector cell responses. Critically we show an unknown feature of boundary vector cells, they have a continuum of excitatory and inhibitory responses to barriers and these responses occur at an orientation of 180o with respect to each other in space, echoing centre-surround organization seen in primary visual cortex. The results in this thesis further understanding on how sensory information about boundaries is encoded and organized and describe the influence of rearing behaviour on the activity of Subicular neurons.

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