The SERNA Conceptual Standard for Neural Correlates of Aging and Cognitive Decline: Definitions, Relationships, and Theoretical Integration (SCS-ACD)

**Background:** Cognitive aging, the gradual decline in cognitive functions such as processing speed, memory, and executive control, is a universal human phenomenon. However, the field is characterized by "terminological chaos," where "normal aging," "mild cognitive impairment (MCI)," and "pre-clinical dementia" are often used inconsistently. **Problem:** This conceptual fragmentation prevents the development of standardized biomarkers for "healthy" vs. "pathological" aging and limits the comparison of results across longitudinal studies. Specifically, the "Brain Reserve" and "Cognitive Reserve" constructs are frequently conflated. **Objective:** To establish the SERNA Conceptual Standard (SCS-ACD), providing canonical definitions and a testable neuro-biological model for cognitive aging. **Approach:** A systematic review of over 450 peer-reviewed articles was conducted, synthesizing evidence from structural and functional neuroimaging, neuropsychology, and epidemiology. **Contributions:** This standard defines 12 canonical terms, establishes the "Scaffolding Theory of Aging and Cognition (STAC-SCS) Extended Model," and proposes 10 falsifiable hypotheses for future research. **Conclusions:** SCS-ACD provides the theoretical infrastructure to transition aging research from descriptive profiling of decline to predictive modeling of neuro-preservation and compensatory plasticity.