Additional Study Information: The purpose of this study is to examine the effect of dietary flavanols on brain activity and memory. Flavanols represent a specific group of plant derived nutrients that are found in cocoa beans, grapes, tea, berries and various other fruits and vegetables. The specific flavanols investigated in this study come from cocoa. Participants will be asked to take cocoa flavanol capsules twice a day over a 12 week period. Study visits will also include cognitive testing sessions, blood draws, questionnaires, and optional MRI scans prior to and after cocoa consumption. Participants will be paid for each cognitive testing and MRI scan, up to a total of $450.