Amyloid-beta accumulation initiates Alzheimer's disease pathology, and tau protein spread is more strongly correlated with cognitive decline than amyloid burden.

Study: Amyloid and Tau Prediction of Cognitive and Functional Decline in Unimpaired Older Individuals: Longitudinal Data from the A4 and LEARN Studies

The study found that while sticky amyloid plaques start the Alzheimer’s process, the spread of tau tangles in the brain is a better sign of when memory and thinking problems will get worse. Blood tests for tau were even better at predicting decline than brain scans for amyloid.

Study: Tau accumulation and atrophy predict amyloid independent cognitive decline in aging

The study found that tau protein spreading in the brain is more closely tied to memory problems than amyloid buildup — even when amyloid is low. But amyloid still seems to be the starting point, because tau only causes big problems in people who already have a lot of amyloid.

Study: Enlarged perivascular spaces in subcortical white matter are linked to amyloid–tau depositions and cognitive decline: Data from a memory clinic in Thailand

This study found that while amyloid buildup happens early in Alzheimer’s, it’s the spread of tau and amyloid together that really links to memory loss — not just amyloid alone. So tau is more closely tied to how bad symptoms get.

Study: Individual gray-white matter functional connection predicts tau spread and cognitive decline in Alzheimer's disease

This study found that where and how fast tau proteins spread in the brain predicts memory loss better than just how much tau is already present. It doesn’t dispute that amyloid might start the disease, but shows tau’s spread is what really makes symptoms worse.