Reference Database & Longitudinal Registry of the Normal and Pathological Aging Brain

For ALL arms: Inclusion Criteria: * Currently resides in The Villages community * Age 50-years and above. * Able to speak, read and understand English * Willingness to participate and able to give informed consent. * If corrected vision: only Glasses should be used during the study testing Exclusion Criteria: * Currently with lice or open wounds on scalp. * Any CNS neurologic disorder * Significant sensory deficits. * Use of a hearing aid that occupies the ear canal * Any neuropsychological disorders * History of special education * Substance abuse in the last 3 months * History of any clinically significant brain trauma as determined by the investigator. * Clinically diagnosed with a concussion in the past year. For Arm 1 Healthy Inclusion Criteria: * BDI score \<14 * Subjects Not meeting diagnostic criteria for MDD per the DSM IV-TR, * MMSE score ≥25 Exclusion Criteria: * Any chronic disease or condition which affects the nervous system as determined by clinical neurological evaluation, medical history or PI discretion. * Any psychiatric disorder, * History of any medication affecting CNS within the last 3 months For Arm 2 Early Alzheimer's Disease Inclusion Criteria: * BDI score \<14 * Subjects Not meeting diagnostic criteria for MDD per the DSM IV-TR, as determined by clinical evaluation by a research clinician and the Mini International Neuropsychiatric Interview (MINI). * MMSE score \<24 * MoCA\<20 * Presence of an early and significant episodic memory impairment Exclusion Criteria: * Any chronic disease or condition other than current pathology * Any other psychiatric disorder * CNS medications within the short period of time prior to the EEG testing which are not in a medically stable treatment phase. For Arm 3 Depression Inclusion Criteria: * BDI score \>14 * Subjects meeting full diagnostic criteria for MDD without psychotic features per the DSM IV-TR * HAM-D 17-item: Total score of 16 or higher at visit 1. Exclusion Criteria: * Any chronic disease or condition other than current pathology * Any psychiatric disorder other than Depression * CNS medications within the short period of time prior to the EEG testing which are not in a medically stable treatment phase. For Arm 4 Mild Cognitive Impairment Inclusion Criteria: * BDI score \<14 * Subjects Not meeting diagnostic criteria for MDD per the DSM IV-TR * MMSE scores according to Number of years of Education: MMSE score Years of Education 17-18 ≤6 20-21 7-8 23-24 ≥10 -20\<MoCA score \>26 Exclusion Criteria: * Any chronic disease or condition other than current pathology * Any other psychiatric disorder * CNS medications within the short period of time prior to the EEG testing which are not in a medically stable treatment phase.