Dedifferentiation in Cognitive Aging: A Scoping Review

This project aims to conduct a comprehensive scoping review of the literature on cognitive dedifferentiation in aging, with a particular focus on how this construct has been operationalized across empirical studies. Aging is associated with widespread changes in brain structure, function, and metabolism, and contemporary network neuroscience frameworks have emphasized that these changes extend beyond morphology to include alterations in large-scale functional organization. Specifically, evidence suggests that aging is characterized by reduced network segregation, decreased modularity, and disruption of hub integrity, reflecting a shift toward more integrated and less specialized patterns of brain activity. Within this context, the dedifferentiation model provides a unifying theoretical account, proposing that aging is associated with a loss of functional specificity and more diffuse recruitment of neural resources during cognitive processing. At the cognitive level, dedifferentiation has traditionally been described in psychometric terms as an increase in the intercorrelation among cognitive abilities across domains. Classical and contemporary studies have reported that general cognitive ability (g) accounts for a larger proportion of variance in older adults, and that changes in different cognitive domains become increasingly coupled over time. However, the empirical evidence remains heterogeneous, with a substantial number of studies—both cross-sectional and longitudinal—failing to support consistent age-related increases in intercorrelations. This inconsistency appears to be driven, at least in part, by methodological variability across studies, including differences in how dedifferentiation is defined and measured (e.g., correlation-based approaches, variance decomposition, or measurement invariance frameworks), as well as variability in sample size and age ranges. Given this heterogeneity, the primary objective of this review is to systematically map and synthesize the different operational definitions and analytical strategies used to study cognitive dedifferentiation. The review will identify key methodological dimensions—such as statistical indicators, study design, and measurement approaches—and evaluate how these choices influence the interpretation of findings. Ultimately, this work seeks to provide a structured and integrative framework for the assessment of cognitive dedifferentiation, with the goal of improving conceptual clarity, enhancing comparability across studies, and informing the design of future research in cognitive aging. Expected outcomes include: (1) a comprehensive taxonomy of operationalizations of cognitive dedifferentiation, (2) a critical appraisal of methodological sources of heterogeneity in the literature, and (3) practical recommendations for standardized approaches to measuring dedifferentiation in both cross-sectional and longitudinal designs. Key terms guiding the search strategy include: “cognitive dedifferentiation,” “dedifferentiation hypothesis,” “terminal dedifferentiation,” “age-related dedifferentiation,” “intercorrelation of cognitive abilities,” and “covariance of cognitive abilities.”