What should we be measuring when we measure cognitive reserve? Distinguishing proxies, prediction, and mechanism.

Cognitive reserve (CR) was proposed to explain why individuals with comparable brain aging or pathology can show different cognitive outcomes. Yet progress in CR assessment has been complicated by ambiguity about what, exactly, is being measured. This Conceptual Analysis distinguishes three elements that are often conflated: experiences proposed to build or maintain reserve, prediction of cognitive outcomes, and the cognitive or neural mechanisms that might produce resilience. The widespread Cognitive Reserve Index questionnaire (CRIq) offers a standardized measure of education, occupational activity, and cognitively stimulating leisure, but combining proposed determinants of reserve does not necessarily measure reserve itself. Similarly, associations between CR proxies and cognitive outcomes establish predictive validity but do not demonstrate that those proxies buffer the cognitive consequences of neural deterioration. Physiological measures potentially move assessment closer to mechanism, but a neural correlate is informative only when its functional meaning and predicted direction are independently constrained. Stronger tests of CR should distinguish and, where possible, independently measure prior cognitive ability, life-course experiences, brain status or pathology, candidate cognitive or neural mechanisms, and cognitive outcomes. On this view, CR may be better understood not as a quantity residing within an individual that can be captured by a single score, but as a theoretically specified pattern of relationships among independently measurable variables. Progress in CR assessment therefore requires movement from proxy to prediction, from prediction to resilience, and from resilience to mechanism.