The late 1960s marks a decisive shift to a pathology-centered understanding of dementia, identifying Alzheimer's disease as a distinct neurodegenerative process characterized by neurofibrillary tangles and amyloid plaques. Ultrastructural evidence and quantitative clinicopathological correlations become central, while the concept of a biological continuum between early-onset and late-onset pathology gains prominence. Research methods emphasize cross-cohort standardization and measurement of histological burden as a proxy for clinical severity.