- As magnetic resonance imaging (MRI) is used to examine the brain in this study, participants will not be included in the study if they have any history of head or eye injury involving metal fragments, some type of implanted electrical device (such as a cardiac pacemaker). If they have severe heart disease (including susceptibility to heart rhythm abnormalities), they should not have an MRI scan unless supervised by a physician. Additionally they should not have a MRI scan if they have conductive implants or devices such as skin patches, body piercing or tattoos containing metallic inks because there is a risk of heating or induction of electrical currents within the metal element causing burns to adjacent tissue. In addition to these guidelines, patients with claustrophobia will not be studied in the MRI elements of this project.