Thanks to positron emission tomography (PET) imaging of tau, which has only recently become available, researchers now report that tau tangles provide a good indication of cognitive decline in later stages of the disease. The study, performed in 10 patients, suggests that while ß-amyloid remains a critical marker for early detection of Alzheimer's, tau may be more useful for tracking disease progression and, potentially, patient response to therapies. Abnormal buildup of ß-amyloid peptides and tau proteins in the brain are major culprits behind Alzheimer's disease, but exactly how the two interact to drive brain cell death has been a subject of debate. PET imaging of ß-amyloid in patients' brains has shed light into its role, especially during early stages of the disease. Taking advantage of newly available tau PET imaging agents, Matthew Brier and colleagues analyzed PET imaging of tau and ß-amyloid in 10 patients with mild Alzheimer's disease and 36 healthy adults. Compared to amyloid plaques, tau tangles in the temporal lobe more closely correlated with cognitive deficits, as measured by a battery of memory tests. Tau deposits in the temporal lobe also strongly associated with tau detected in the patients' cerebrospinal fluid. The findings, which are consistent with current hypotheses, propose tau as a better predictor than ß-amyloid of dementia during Alzheimer's disease progression.