A Study of Neurodegeneration and Neuronal Fluctuations in Lewy Body Disease and Alzheimer's Disease

Inclusion Criteria: * Use English as their primary language. * Be willing to undergo health and cognitive assessments, as well as brain MRI and EEG study. * Will be encouraged to have an available study partner (also called a "co-participant") who is familiar with the participant's daily functioning. * This study will be limited to healthy individuals, and patients who have a clinical diagnosis made by a board-certified neurologist of Lewy body disease or Alzheimer disease. * All individuals must be capable of providing informed consent and complying with the trial procedures. Realizing the challenge of obtaining informed consent from cognitively impaired individuals, time is specifically scheduled to foster an informative, supportive interview with the participant and caregiver/legal guardian (typically a spouse or child according to Arizona law and IRB guidelines). * Ongoing participation will be maintained by strict adherence to inclusion/exclusion criteria, clinical appropriateness (as determined by participant's physician and proxy/family), as well as by expressed wishes of family members/caregivers/proxy discussed at each study visit (as appropriate). * All participants will receive copies of the signed ICFs (including signatures of those obtaining consent). * All participants have the right to withdraw from the study at any time. Exclusion Criteria: * Individuals will be excluded if they have significant sensory (visual and hearing) deficits or major medical or psychiatric illnesses which would limit participation. * Participants will also be excluded if they have history of other major neurologic disorders including stroke, epilepsy, meningitis/encephalitis, metabolic or toxic encephalopathy, penetrating or severe closed head injury, brain tumor/other structural lesion, other primary movement disorders (such as essential tremor, dystonia, chorea, multiple system atrophy, progressive supranuclear palsy, corticobasal syndrome). * In addition, as necessitated by the risks of Magnetic Resonance Imaging (MRI), patients who have any type of implanted electrical device (such as a cardiac pacemaker or a neurostimulator including deep brain stimulation), or a certain type of metallic clip in their body (i.e., an aneurysm clip in the brain), are not eligible for participation in the MRI portion of the study. Individuals who experience claustrophobic anxiety will also be excluded from participation. * Women who are or might be pregnant and nursing mothers are not eligible. * If the subject is a woman of childbearing potential, due to unknown risks to the fetus, they must have a pregnancy test. Individuals who have a history metalworking involving cutting processes such as grinding, filing, shaving, and threading, or history of eye injury involving metal, will also be excluded unless they have had prior documented radiological clearance for MRI.