Dissociating the mechanisms of Tau PET and cortical atrophy underlying memory deficits in typical and atypical prodromal Alzheimer's disease

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The proposed research examines the mechanisms underlying memory encoding versus storage deficits, in typical and atypical AD at the stage of mild cognitive impairment, by delineating the specific roles of amyloid, tau, and cortical atrophy as potential drivers of this impairment both cross-sectionally and longitudinally. A long-term goal of the research program is to improve clinical prognostication and outcomes monitoring by expanding our knowledge of the mechanisms of memory encoding impairment across the AD spectrum, with a focus on better characterizing the atypical presentations of AD (i.e., posterior cortical atrophy; PCA, and logopenic variant primary progressive aphasia; lvPPA). The proposal builds upon preliminary evidence showing that memory encoding, in contrast to memory storage, relies on cortical networks outside the medial temporal lobes in typical and atypical AD, and that auditory-verbal working memory deficits impact encoding and retrieval, but not storage, in PCA. The candidate’s preliminary work also demonstrated that visual space and face perception deficits, which may be critical contributors to memory encoding, are sensitive to AD-related tau and atrophy in visual association regions in PCA and lvPPA. We will build on this preliminary work by examining these processes in relation to different stages of memory (encoding vs storage), and in relation to imaging biomarkers of AD pathology. The first aim is to examine the impact of visual or auditory-verbal processing impairment on associative memory encoding and storage, in relation to tau and amyloid pathology, across the spectrum of prodromal AD. The second aim is to investigate the mediating effect of cortical atrophy and moderating factors, including age at symptom onset, that may explain this relationship between tau pathology and memory. Short-term training goals for these aims include obtaining expertise in tau and amyloid PET processing that will further the candidate's long-term goal of utilizing multimodal neuroimaging with cognitive outcome measures to prognosticate disease course across the AD phenotypic spectrum. The third aim is to determine the longitudinal impact of tau spread on atrophy and progressive memory decline across the spectrum of prodromal AD. Training for this aim will extend the candidate's expertise into longitudinal biostatistical analysis, including morphometric analyses to quantify and control for the effect of gray matter loss in the prodromal AD population. All aims will utilize data collected from the novel associative memory tasks outlined in the proposed project. All other clinical and neuroimaging data will be provided by the primary mentor’s NIH-funded studies. Training available at Massachusetts General Hospital and the Harvard Medical School community allows access to resources and mentorship in the specific techniques necessary for the completion of the proposed aims and the candidate's training and career goals.