Digital Biomarkers for Early Cognitive Decline: Clinical Promise, Limitations, and Validation Pathways

There is increasing global concern regarding the growing burden of cognitive decline and dementia, particularly because existing diagnostic tools often fail to detect subtle preclinical changes. Early detection is critical to enable timely intervention, yet these limitations hinder effective clinical management and opportunities to slow disease progression, underscoring the need for complementary methods that provide objective, continuous, and sensitive measures of cognitive function. Digital biomarkers, defined as quantifiable metrics derived from mobile devices, online technologies, and wearable sensors, offer a promising approach for enhancing early detection when integrated with traditional cognitive assessments and biological markers. This report critically reviews digital biomarkers across multiple domains, including speech, behavior, cognition, and motor function, and evaluates their capacity to identify early cognitive alterations. Key challenges related to clinical integration, study design, analytical methods, standardization, and consistency of practice are examined, alongside the advantages of multimodal and longitudinal assessment approaches. While digital biomarkers have demonstrated sensitivity to subtle cognitive changes, significant operational, methodological, and validation challenges remain, particularly with respect to reproducibility, accessibility, and equity. By providing a balanced synthesis of the clinical promise and current limitations of digital biomarkers, this review aims to inform future research priorities, support rigorous validation pathways, and guide the development of clinically useful, ethically designed, and validated digital tools for the early monitoring of cognitive decline.