Howard, LR; (2013) Hippocampal representations of spatial relationships in visual scenes and during real-world navigation. Doctoral thesis , UCL (University College London).

Abstract

It is well established that the hippocampus, and surrounding medial temporal lobe (MTL) regions, plays a critical role in episodic memory formation and spatial navigation. In this thesis I used fMRI to examine these two processes, with a common focus of identifying the types of spatial relational information represented in the hippocampus. First, I investigated whether item-context binding, in visual scenes, is a specific function of the hippocampus. In this study I used hippocampal novelty signals in response to changes in the spatial relationship between items and backgrounds, to determine the computational mechanism supporting this process. In doing so, I show that item-context binding is a specific function of the hippocampus and that this region detects changes in spatial relational information through its function as an associative match-mismatch detector. Second, I examined the role of the hippocampus in goal-directed navigation, with the specific aim of determining how this region tracks the spatial relationship (distance) between a navigator’s current position and the location of their intended goal. The data from this study revealed that a dynamic goal-tracking system operates within the MTL, with different regions encoding specific spatial metrics at different time points during navigation. This dynamic goal-tracking system challenges current computational models of navigational guidance and helps to explain previous contradictory findings. Together, the data from these two studies provide compelling evidence for the hypothesis that the main role of the anterior hippocampus is to act as a comparator.

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