The main purpose of this study is to clarify the the physiology of the early phases of cognitive impairment in older age. Specifically, we aim to clarify the associations among synaptic density, learning-related synaptic plasticity, blood-based biomarkers of Alzheimer’s Disease (AD)-related proteinopathy, and cognitive performance in mild NeuroCognitive Disorder (NCD); and clarify these associations early in development of major NCD/dementia.