The goal of this proposal is to develop and validate an early, non-invasive, quantitative marker for the pre-clinical stage of Alzheimer's disease (risk marker) using functional magnetic resonance imaging (fMRI). Such a sensitive marker for AD will have significant advantages in identifying people at risk, facilitating early assessment and providing effective disease management. Recent developments in fMRI technology allow us to indirectly observe neuronal activity with high spatial and temporal resolution. We and others have observed spontaneous low frequency (SLF) fluctuations in the BOLD contrast-weighted neurophysiological signal in subjects at rest. We have developed an index, the COSLOF index, to quantify changes of SLF signal. The results of numerous published neuropathological studies suggest that the hippocampal formation is the initial locus in the disease processes of AD. In addition, the progression of neurodegenerative changes is remarkably uniform across individuals, is predictable, and shows little inter-patient variation. In AD, the lesions eventually lead to severe damage to the hippocampus (referred to as the """"""""floor effect"""""""") and clinical expression of dementia. Our preliminary results demonstrate that the COSLOF index has the ability to distinguish between probable/possible AD patients and cognitively healthy controls. Based on all these results, we propose a prospective and longitudinal study to test the hypothesis that the COSLOF index in the hippocampal formation can predict the onset of AD dementia in subjects with mild cognitive impairment (MCI). We chose to study MCI subjects because of their high incidence (yearly 10-12 percent) of AD development. At the end of the five-year period, we can determine retrospectively the sensitivity of the COSLOF index to predict the pre-clinical onset of AD progression and to distinguish those MCI subjects who are destined to develop AD from those who are undergoing normal aging processes.
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