Objective Detection of focal brain tau deposition during life could greatly facilitate accurate diagnosis of Alzheimer’s disease (AD), staging and monitoring of disease progression, and development of disease modifying therapies. Methods We acquired tau positron emission tomography (PET) using 18F T807 (AV1451), and amyloid-β PET using 11C Pittsburgh Compound B (PIB) in older clinically normal individuals, and symptomatic patients with mild cognitive impairment or mild AD dementia. Results We found abnormally high cortical 18F T807 binding in patients with mild cognitive impairment and AD dementia compared to clinically normal controls. Consistent with the neuropathology literature, the presence of elevated neocortical 18F T807 binding particularly in the inferior temporal gyrus was associated with clinical impairment. The association of cognitive impairment was stronger with inferior temporal 18F T807 than with mean cortical 11C PIB. Regional 18F T807 was correlated with mean cortical 11C PiB among both impaired and control subjects. Interpretation These findings suggest that 18F T807 PET could have value as a biomarker that reflects both the progression of AD tauopathy and the emergence of clinical impairment.

Summary Alzheimer's disease (AD) has been associated with functional alterations in a distributed network of brain regions linked to memory function, with a recent focus on the cortical regions collectively known as the default network. Posterior components of the default network, including the precuneus and posterior cingulate, are particularly vulnerable to early deposition of amyloid β-protein, one of the hallmark pathologies of AD. In this study, we use in vivo amyloid imaging to demonstrate that high levels of amyloid deposition are associated with aberrant default network functional magnetic resonance imaging (fMRI) activity in asymptomatic and minimally impaired older individuals, similar to the pattern of dysfunction reported in AD patients. These findings suggest that amyloid pathology is linked to neural dysfunction in brain regions supporting memory function and provide support for the hypothesis that cognitively intact older individuals with evidence of amyloid pathology may be in early stages of AD.

Key Points Question Is cognitive decline associated with amyloid-β or tau tangles accumulation? Findings In this cohort study that included 60 normal older adults with repeated positron emission tomography measures, the rate of tau accumulation in the inferior temporal neocortex was associated with the rate of cognitive decline. Amyloid accumulation was associated with subsequent tau accumulation, and this sequence of successive amyloid and tau changes in neocortex was found to mediate the association of initial amyloid with final cognition, measured 7 years later. Meaning Amyloid positron emission tomography is useful to detect early Alzheimer pathology; repeated tau positron emission tomography is useful to track disease progression.