Cognitive training focused on processing speed delivered a 33% reduction in dementia incidence across two decades of follow-up, while memory and reasoning exercises showed no protective effect. The ACTIVE trial tracked 2,802 adults aged 65-94 through multiple interventions and found only speed-of-processing training maintained its neuroprotective benefits long-term. This selective efficacy suggests that timing-based cognitive challenges may strengthen neural efficiency in ways that traditional memory drills cannot replicate. The finding aligns with emerging evidence that processing speed decline precedes other cognitive deterioration in aging, potentially serving as an early intervention target. However, the protective mechanism remains unclear—whether speed training builds cognitive reserve, delays neural aging, or enhances compensatory networks requires further investigation. The research carries practical weight because processing speed can be trained through accessible digital platforms, unlike complex memory strategies that require sustained instruction. While promising for prevention strategies, the study's older cohort and single-intervention design limit broader applications. The challenge now involves translating these clinical protocols into engaging, scalable formats that younger adults might adopt proactively rather than reactively.