Forgetting across a hierarchy of episodic representations

• Published in: Current opinion in neurobiology Vol. 67; pp. 50 - 57
• Main Authors: Andermane, Nora, Joensen, Bárður H, Horner, Aidan J
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2021
• ISSN: 0959-4388; 1873-6882
• DOI: 10.1016/j.conb.2020.08.004

•Episodic events are hierarchically represented across distinct brain regions.•The mechanisms of forgetting differ across distinct levels in the episodic hierarchy.•Episodic event representations are forgotten in a dependent ‘holistic’ manner.•Item-based representations are forgotten in an independent ‘fragmented’ manner. Rich episodic experiences are represented in a hierarchical manner across a diverse network of brain regions, and as such, the way in which episodes are forgotten is likely to be similarly diverse. Using novel experimental approaches and statistical modelling, recent research has suggested that item-based representations, such as ones related to the colour and shape of an object, fragment over time, whereas higher-order event-based representations may be forgotten in a more ‘holistic’ uniform manner. We propose a framework that reconciles these findings, where complex episodes are represented in a hierarchical manner, from individual items, to small-scale events, to large-scale episodic narratives. Each level in the hierarchy is represented in distinct brain regions, from the perirhinal cortex, to posterior hippocampus, to anterior hippocampus and ventromedial prefrontal cortex. Critically, forgetting may be underpinned by different mechanisms at each level in the hierarchy, leading to different patterns of behaviour.