Group-to-individual generalizability and individual-level inferences in cognitive neuroscience

• Published in: Neuroscience and biobehavioral reviews Vol. 169; p. 106024
• Main Authors: Mattoni, Matthew, Fisher, Aaron J., Gates, Kathleen M., Chein, Jason, Olino, Thomas M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01.02.2025
• Subjects: Brain - physiology; Cognitive Neuroscience; Ergodicity; Group Processes; Heterogeneity; Humans; Idiographic; Individuality; Precision Imaging; Stationarity; Heterogeneity; Ergodicity; Stationarity; Precision Imaging; Idiographic
• ISSN: 0149-7634; 1873-7528; 1873-7528
• DOI: 10.1016/j.neubiorev.2025.106024

Much of cognitive neuroscience research is focused on group-averages and interindividual brain-behavior associations. However, many theories core to the goal of cognitive neuroscience, such as hypothesized neural mechanisms for a behavior, are inherently based on intraindividual processes. To accommodate this mismatch between study design and theory, research frequently relies on an implicit assumption that group-level, between-person inferences extend to individual-level, within-person processes. The assumption of group-to-individual generalizability, formally referred to as ergodicity, requires that a process be both homogenous within a population and stationary within individuals over time. Our goal in this review is to assess this assumption and provide an accessible introduction to idiographic science (study of the individual) for the cognitive neuroscientist, ultimately laying a foundation for increased focus on the study of intraindividual processes. We first review the history of idiographic science in psychology to connect this longstanding literature with recent individual-level research goals in cognitive neuroscience. We then consider two requirements of group-to-individual generalizability, pattern homogeneity and stationarity, and suggest that most processes in cognitive neuroscience do not meet these assumptions. Consequently, interindividual findings are inappropriate for the intraindividual inferences that many theories are based on. To address this challenge, we suggest precision imaging as an ideal path forward for intraindividual study and present a research framework for complementary interindividual and intraindividual study. •Theories are often intraindividual, yet study designs are mostly interindividual.•Idiographic science informs assumptions of group-to-individual generalizability.•Heterogeneous and non-stationary patterns prevent assuming this generalizability.•Intraindividual study designs are needed for intraindividual inferences.•Precision imaging is a necessary path forward for intraindividual study.