Defining 'Successful' Episodic Memory Ageing: Implications of Methodological Heterogeneity.

Episodic memory changes as we age, ranging from marked decline in Alzheimer's disease to exceptional preservation in some older adults. Older individuals with episodic memory exceeding typical age-related performance are often termed 'superagers'. Previous studies have used varying age ranges, reference benchmarks to distinguish successful from typical ageing or memory assessment tasks. Despite major advances in the field, the marked heterogeneity in defining superageing can hinder progress if not considered when interpreting results. We conducted a scoping review, using systematic searches of MEDLINE and Scopus, identifying 78 eligible studies. This review investigates the main sources of variability in superager definition across the following domains: age criteria, episodic memory criteria, and other cognitive criteria. We demonstrate how variation in each domain alters the composition of the target group and the implications for interpreting cognitive and neural mechanisms of superageing. Rather than establishing a hierarchy of definitions, we propose a conceptual framework to facilitate cross-study comparison and identify gaps in the literature. Understanding the implications of each selection criterion will enhance the interpretability of findings and accelerate insights into the superageing phenotype, ultimately contributing to better understanding of healthy episodic memory ageing.