The goal of this study is to develop a new technique to detect early stages of deterioration in a part of the brain associated with memory: the hippocampus. A new type of brain scan, the 7-Tesla MRI, allows us to view the hippocampus in detail. We aim to detect the earliest stages of memory change among young people who may be overweight, depressed or at risk for diabetes, in order to identify those who may be at risk for dementia later in life.