Inclusion Criteria:  5 individuals with moderate to severe dementia, 5 with mild stage dementia, 5 with amnestic MCI, 5 presymptomatic APOE e4 carriers, and 5 age, sex, and education matched APOE e4 noncarriers. Additionally we will include a group of 5 patients with mild to moderate stage dementia with Lewy bodies (DLB), the second most common degenerative dementia, to explore differences from clinically typical Alzheimer's disease patients given the known clinical differences in EEG dysrhythmic severity between them (total of 30). Unimpaired APOE e4/4 homozygotes age 65-75 and APOE e3/4 heterozygotes age 75-85 for the preclinical AD subset and age, sex, and education matched APOE e4 noncarriers for the unaffected controls. Biomarker confirmation for preclinical diagnosis will be utilized to the extent possible (a subset of 130 members of our cohort have undergone amyloid-PET resulting in approximately 45 who are amyloid positive).  Exclusion Criteria:  Previous stroke. Severe head injury. Craniotomy. Any other potentially confounding neurologic illness (typically anything that causes structural brain damage). Psychoactive medication use will not be an absolute exclusionary criterion in patients with moderate to severe dementia but patients who are relatively drug-free will be prioritized to the extent they are available within the study period. Psychoactive drug use will be exclusionary in the prospectively obtained clinical patients.