This project will examine the relationship between physical activity levels, brain structure and memory function in adults with Mild Cognitive Impairment (MCI) aged 60 to 75. The study will follow 30 adults with age-associated memory impairment or MCI over the course of 18 months. During this time, subjects' physical activity levels will be measured regularly and related to both the thickness their hippocampus and to their memory performance. Subjects will be recruited and screened for major health problems at UCLA. Physical activity will be tracked for two weeks using accelerometers at baseline and every 6 months during the study. At baseline and at the end of the study, subjects will undergo a structural MRI brain scan to measure hippocampal thickness, as well as a neuropsychological evaluation to measure memory function. The study will seek to determine the relationship between physical activity level, hippocampal thickness and memory performance in older adults with age-associated memory impairment.