Hippocampal Contributions to Gist and Detail Constructs of Episodic Memory

Abstract

Cognitive theories like Fuzzy Trace Theory or Multiple Memory Trace Theory have implied a distinction between coarse- and fine-grained processing of details for constructs of episodic memory. These distinctions in memory constructs possess similar attributes when compared to specialized functional processing of the anterior and posterior hippocampus segments, being pattern completion and pattern separation. This study attempted to combine both behavioural and imaging theories to uncover the neural mechanism responsible for the distinction in memory type. Participants viewed a 20-minute short film, interleaved with 5-minute rest segments, and later gave a free recall of the film. Free-recall audio files were transcribed and analysed for content, assessing the composition of gist and detail statements. These transcript scores were regressed onto hippocampal segment volume to reveal the predictive value of hippocampal segment volume on memory type. The results of this study showed larger left anterior and smaller right posterior hippocampal volume predicted more detail statements in a free recall transcript. Additionally, this study attempted to show the mechanism by which gist memory representations were consolidated. Using Representational Similarity Analysis, encoding and rest fMRI data were analyzed to observe whether the re-emergence of encoding patters could predict successful recall. While the data did not support this theory, results from this study provided valuable methodological insights for future data collection involving complex naturalistic stimuli.