BDNF and Alzheimer disease: Based on these insights, future directions in AD research and intervention may include (1) developing neurogenesis-based indices (e.g., the NII) as a quantitative biomarker for pathological staging and diagnostic evaluation; (2) designing neurogenesis-modulating strategies to enhance cognitive performance and emotional regulation in both preclinical and clinical settings; (3) prioritizing drug discovery targeting key neurogenic regulators, such as BDNF/TrkB signaling, the Wnt/β-catenin pathway, and Notch1 receptor activity.