The Demands of Episodic Memory on Hippocampal Function in Rats and Humans

Abstract

This thesis sought to explore episodic memory, interference caused by similar events and its demands on hippocampal function by using different methodological and practical approaches in humans and rodents. Overall, this thesis focused on three aims, which included methodological approaches to testing episodic memory, using this approach to investigate cholinergic depletion of the hippocampus, and linking animal and human behavioural research. The recent development of spontaneous recognition tasks in rats to assess multiple trials consecutively in one testing session allow an opportunity to assess the role of contextual changes and interference in episodic memory. In a series of studies, it was shown that a new continuous trials apparatus can be used in behavioural as well as lesion studies to further explore the role of acetylcholine involved in episodic memory in rats without causing any proactive interference. Furthermore, the behavioural tasks in this thesis emphasise that context, which can take various forms, plays a profound role in segmenting memory of events. Whereas increasing the number of trials happening consecutively normally did not produce interference between events remembered, contextual representation within those trials was crucial. Chapters 2-7 demonstrated that depending on the context’s nature it enhances the segmentation of similar episodes and avoids interference, but it can also hinder recollection of events. Chapter 8 supplemented these findings by providing evidence in humans, where a clear deficit in recollection was found when a spatial change in a virtual environment was encountered, revealing a location updating effect. However, further validation of the human episodic memory task is necessary to make it a useful method in assessing different forms of hippocampal mechanisms involved in episodic memory.