Understanding Episodic Memory in Animals and Humans: A Methodological Approach.

Abstract

This thesis sought to explore two different methodological approaches to episodic memory, namely episodic memory as demonstrated in humans and episodic-like memory as demonstrated in animals.

The results of Chapter 2 were successful in demonstrating episodic-like memory in the rat using recollection alone, despite the fact that performance in this study was significantly poorer compared to the original (Eacott, Easton, & Zinkivskay, 2005). Subsequent experiments within this chapter highlighted potential methodological issues (e.g. interference of odour cues, stability of performance over lengthy testing periods) that impact on such spontaneous tasks.

Chapter 3 investigated the effect of bilateral lesions to the hippocampus on episodic-like memory. The results of Chapter 3 were not in agreement with previous findings as none of the three groups (Sham Group/Partial Hippocampal Group/Hippocampal Group) showed evidence of episodic-like memory. In depth analyses of the three groups lead the author to the conclusion that this was not due to an ineffective task but due to extraneous factors impacting upon the performance of the animals. Analyses of D2 scores and raw exploration times in both phases of the experiment also highlighted the importance of D2 scores in determining object familiarity.

Chapter 4 further investigated the effect of bilateral lesions to the hippocampus on episodic-like memory in animals using an Open Field arena. The addition of landmarks to the testing room resulted in the Sham group successfully demonstrating episodic-like memory whilst the Hippocampal lesion group remained at chance levels. As there was no significant difference between the two groups it was not possible to conclude that this was as a result of the lesions to the hippocampus. The control task showed neither group demonstrating memory for the more simple ‘what-where’ task, therefore it was concluded that a problem with the methodology still remained. Subsequent experiments within this chapter investigated cleaning methodology, the stability of performance over time, and the effect of task change on performance. The clear variability in the data over lengthy testing periods emphasised the sensitivity of such tasks.

Chapter 5 aimed to investigate whether applying comparable ‘What-Where-When’ and ‘What-Where-Which’ tasks to human investigations of episodic memory would result in similar patterns of data with regard to recollection and familiarity. Analysis of the results revealed the use of other strategies to solve the episodic ‘What-Where-When’ questions. Subsequent experiments within this chapter aimed to confirm the use of strength of memory trace as a strategy for solving these episodic questions. Results from the final experiment suggested that other strategies were also being employed in addition to strength of memory trace. Conclusions were drawn regarding the individual components of episodic memory and their susceptibility to interference from other strategies.

Overall conclusions focused on the definition of episodic memory and the potential implications of alternative strategies impacting on such tasks.